MANSONELLA, SPECIES, VECTORS AND WOLBACHIA IN AFRICA
Table of Contents
Monsonella perstans 4
The biology of Monsonella perstans 5
Epidemiology of Mansonella perstans 6
Clinical features of Mansonella perstans 8
Diagnosis of Mansonella perstans 8
Treatment of Mansonella pertans 9
CASE STUDY 10
Mansonella ozzardi 14
The biology of Mansonella ozzardi 14
Clinical features of Mansonella ozzardi 17
Detection of Mansonella ozzardi 18
Treatment of Mansonella ozzardi 19
Monsonella streptocerca 19
The biology of Mansonella streptocerca 20
Epidemiology of Mansonella streptocerca 22
Clinical features of Mansonella streptocerca 23
Diagnosis of Mansonella streptocerca 23
Treatment of Mansonella streptocerca 23
MANSONELLA AND A POTENTIAL NEW SPECIES IN GABON 25
Diagnosis of Mansonellosis 30
Biology of Wolbachia 34
Epidemiology of Wolbachia 35
Treatment of Wolbachia 35
MANSONELLA-WOLBACHIA RELATIONSHIP 36
The research paper explored the information and updates about Mansonellosis infection in Africa. Being one of the filarial infections, this paper is an emphasis on the three major species of Mansonella, areas of prevalence which are not limited to African countries, clinical features including the asymptotic ones and treatments which have proven to effective and the ones that have been futile. The species Mansonella perstans, Mansonella ozzardi and Mansonella streptocerca are the three species together with their dates of discovery in the African continent.
The information provided in this paper also explored the endosymbiont bacteria Wolbachia, its vectors which are the mode of transmission, clinical features, morphology, and treatment. Explored and discussed in detail is how Wolbachia can be used as an alternative method in the elimination of Mansonella through its own medication using the methods that are discussed.
The life cycle of the various species is also discussed in detail followed by a simplified diagrammatic representation to aid in understanding. Various epidemiological maps are also included in the paper as a way to represent its prevalence diagrammatically.
There are also control mechanisms discussed especially those living along the coastal areas and the belt of tropical rainforest. The aim of infection control is to prevent the vulnerability of acquiring an infection by implementing infection control programs. For instance education on the importance of healthy living among families, environmental hygiene awareness and outbreak management.
In conclusion, approximately 114 million people in Africa, mostly located in 33 Sub-Saharan African countries, are infected with Mansonella parasites. The ability of Mansonella to induce severe clinical symptoms has only been lately considered. However, no study has clarification on its burden in patients in Gabon, a tropical African country where parasitic illnesses are common
MANSONELLA, SPECIES, VECTORS AND WOLBACHIA IN AFRICA
Introduction: Infectious diseases are still a source of serious challenges in most of the African countries and the world in general. This, therefore, has been a significant barrier in the realization of sustainable development goals, universal health care being among them. “These maladies together constitute 20% of mortality in all age groups and 50% of child mortality. In the past 20 years, the major increase in funding has enabled significant progress to be made in the fight against these infections”. (Clinical Infection Diseases volume 65, pages 65-67). However, with the quick increase in knowledge and advancement in technology, serious researches have been made and most of these infections have been contained including the three serious killer maladies: malaria, tuberculosis, and human immune deficiency virus. Likewise, one of the most neglected and understudied filarial infection, Mansonellosis has also infested and affected most of these African countries with its dominance in the West African countries. Mansonellosis is therefore a vector-borne human infection that is as a result of three species of filariae that uses human as their specific reservoir namely: mansonella perstans formerly called Dipetalonema perstan, mansonella ozzardi and mansonella streptocerca also initially called Dipetalonema streptocerca. The disease is mainly common in tropical and subtropical Africa and is mainly transferred from one person to the next through a female sucking flies called midges or black flies. The disease affects the low income population in endemic areas of Africa and is considered mild as its health related effects are unknown and therefore treatment has not been properly defined.
Monsonella reservoirs consist of many species of primates, carnivores, ungulates, rodents and tupaids in tropical Africa. Three Mansonella species often infect humans: Mansonella perstans, M. ozzardi and M. streptocerca. While Mansonella perstans has never been identified to infect non-human primates, Mansonella streptocerca has been found in primates. Only humans appear to be naturally infected with Mansonella ozzardi, African patas monkeys (Erythrocebus patas), but not chimpanzees, rhesus, capuchin or squirrel monkeys that are vulnerable to experimental infection with these species. Chimpanzees in Central Africa are the hosts of Mansonella rodhaini, which has been identified in skin biopsy samples of most villagers in Gabon.
The three species causing Mansenollis can be differentiated from each other by their morphological characteristics. A sensitive test called polymerase chain reaction (PCR) can also be used to distinguish these species. Since the infection is neglected and understudied, there is no international organization or program put in place to manage its spread and define proper treatment strategies. This is as a result of its asymptomatic nature as its clinical features are not universally agreed on.
The distributions of these species of Mansonella are sketchy and hard to define. This is because the symptoms of these infections varies from one endemic area to the next. Also, unlike other infections, surveys and other examinations carried on these species are proving hard to justify. “Their adult worms of Mansonella are viviparous and can produce a lot of microfilariae until they die. In the case of mansonella ozzardi and mansonella perstans the microfilariae are produced and can be found in the blood while that of mansonella streptocerca reside subcutaneously.”(Carlos Brisola Marcondes (eds), Arthropod-borne diseases, Springer international publishing, 2017)
The three diagrammatic representation of the microfilariae of the three nematodes are as shown below.
a. Mansonella ozzardi b. Mansonella perstans c. Mansonella streptocerca
Source: (Carlos Brisola Marcondes (eds), Arthropod-borne diseases, Springer international publishing, 2017).
Monsonella perstans: It is considered one of the dangerous nematodes that causes serious cavity filariasis in human beings. The species belongs to the phylum Nematoda of onchocerciasis Family. It is mainly transmitted by small sucking blood flies or the biting midges and it’s widespread in sub-Saharan Africa. “Mansonella persatans is a human filarial nematode that is highly prevalent in some areas across sub-Saharan Africa and South America. It is little known but widespread human filarial parasite”. (Clinical infectious diseases volume 65). “Approximately more than 100 million human beings may be infected and about 600 million people living in 33 nations are at a greater risk of Mansonella perstans infection in Africa alone” (clinical infectious diseases volume 65).The adult worms of these species mainly find reservoir in the following areas; pleural, pericardial and the peritoneal cavities and in the retroperitoneum tissues and mesentery. Perstans filariasis is often associated with peripheral blood eosinophilia and anti-filarial antibody increment. The infection of the disease is reported in thirty three countries with its prevalence high in endemic areas, and also among young population as children. Despite its widespread among human population, it is often understudied and no definite treatment is known or has been established. It can therefore be classified as one of the neglected tropical epidemics. One reason associated with this is that it occurs among the less fortunate population and that it has not been associated with clear and definite clinical symptoms. Much of the information concerning Monsonella perstans has therefore been obtained from studies of other filarial parasites such as Loaloa, Onchocerca volvulus and Wuchereria bancrofti in which each was found to contain Monsonella perstans as a co-inhabitant. The female species of Mansonella pertstans are viviparous and often produce tiny larvae are known as microfilariae which always find its way into the blood circulation. The microfilariae are usually picked up by vectors when they consume a blood meal and after some time of development in the host, parasites may be transmitted to a new human reservoir. Although an effort is being put to control other filarial infections such as onchocerciasis and lymphatic filariasis, little attention is paid to Mansonella perstans as the three occur at the same or in the same geographical location. However, this infection requires serious control measures as well as its symptoms though maybe hidden for sometimes, it could severely interfere with the host defense mechanisms against other illness or the results of other diseases as malaria that thrive in the same environment
The biology of Monsonella perstans
The biology of an organism is defined as the study of its morphology, physiology, anatomy, behavior, origin, and distribution. Therefore each of the species of Monsellosis has its own unique biological composition as discussed below. First is the biological composition of the nematode Monsonella perstans. The host acquires the infection when infective larvae consume on their blood meal while for other filarial diseases it is often the body temperatures that trigger the infected larvae to penetrate the dermis. However, the development of this larvae up to maturity and the period taken is unknown as it is rare to find an adult worm. They can be found however in some connective tissues in cavities during autopsy or surgery. “Following the original descriptions, more recent details on the morphology of the adult worms have been given by Eberhard and Orihel (1984) and Baird et al (1987). They are cylindrical in shape, the female measures 50-80 mm x 80-120 μm and the male 35-40 mm x 50-60 μm”. (Agbolade and Akinboye 2001 O.M. Aboglade, D.O Akinboye)
The center for Diseases and control, however, summarized the life cycle in the following simple paragraph with an illustrated model for easy comprehension as shown. “When the midge consumes on a blood meal, an infected midge or flies introduces third-stage filariae larvae onto the dermis of the human reservoir where they can penetrate into the bite wound. They grow into adult worms that reside in host’s cavities, most preferably the peritoneal cavity or the pleural cavity but least commonly in the pericardium. The size usually ranges from 70-80 mm in length for females and 120 μm in width and their male counterparts measures close to 45mm by 60 μm. Adults produce unsheathed and sub periodic microfilariae during a blood meal. After the blood meal consumption the microfilariae move from the midge’s midgut via the hemocoel to the thoracic muscles of the vector parasite. There the microfilariae then grow into first-stage larvae that then develop to a third-stage infective larvae. This third-stage infective larvae then move to the midge’s proboscis and can transfer the infection to another host when the vector consumes a blood meal”. (“https:www.mcdinternational.org/trainings/malaria/filaris/body_filaris_Monsonella perstans#life cycle”
The above summary can be wrapped up in the following diagrammatic representation of first-stage larvae up to the third stage infected larvae.
Source courtesy of: www.cdc.gov/parasites
Epidemiology of Mansonella perstans
The distribution of the filarial Mansonella perstans is wide in the African continent with exclusion of the Northern countries such as Mauritania, Morocco, Algeria, Tunisia, Libya, Egypt), southern (South Africa, Botswana, Lesotho, Swaziland, Namibia) and western (Eritrea, Ethiopia, Djibouti, Somalia) areas and island countries such as (Madagascar, Comoros, Mauritius, Seychelles, Cape Verde) from which its infestation has not been identified. “Based on information available at that time, an estimate of about 19 million people in Africa were infected with Mansonella perstans. With an increase in the African population of about six times since then, this would correspond to about 114 million infected people in Africa today (thus giving an average prevalence of about 20% for the endemic countries). Although this figure is a gross estimate, it could, in reality, be higher considering that new endemic foci are being reported regularly from different zones of Africa and that available data are based only on the detection of microfilariae. The large growth in urban and semi-urban areas, on the other hand, is not likely to have contributed to an increase in the number of Mansonella perstans infected persons, as this infection appears to be essentially rural”(N.R Stoll, This wormy world J,Parasitol. ,33(1947, page 1-18)). Information regarding the suitable conditions favoring the transfer of Monsonella perstans is reported to be deficient. However high dominance was found where the tropical rainforest with the vast swamps alternated and open ground. It is readily diagnosed in the rainforest while least found in the less forested areas and mountainous regions. In some studies, it was found that the rotting banana plants provided a good breeding place for the vector and therefore could be a suitable factor aiding its transmission. However, when some studies were conducted in areas of dense banana cultivation, the result was void of the existence of Mansonella perstans. In areas of high prevalence, its severity increased with age with most adults showing high levels. “This, and the fact that microfilariae may also be seen in many young children, even below 5 years of age, distinguishes the age pattern of Mansonella perstans microfilaraemia from that of Wuchera bancrofti, and may suggest that development of host resistance to Mansonella perstans infection is weak and that people continue to be susceptible to new infections even at old age”.(S.M Asio, P.E Simonsen, A.W Onapa: Mansonella perstans filariasis in Uganda : patterns of microfilaraemia and clinical manifestations in two endemic communities).
The distribution of filariasis Mansonella perstans is as shown below:
Clinical features of Mansonella perstans
The first of the Mansonella species to be discovered by Sir Patrick. Originally it was described by the morphological features of its microfilariae. Hence, like any other filarial infection of Mansonella species, this disease has its own symptoms associated with it. These symptoms are normally asymptomatic in nature and are not commonly accepted. The signs attributed to his filarial infection are: swellings of the subcutaneous tissues, pericarditis, ocular symptoms including blindness and pruritus. Symptoms that are not definite include fever, fatigue, pruritus, arthralgia, and sometimes abdominal pains may occur. In a few cases, headache and neuropsychiatric signs may be identified. Its pathogenic nature has not however been clearly defined due to its rare occurrence. Also, some of the symptoms of this infection rarely manifest and therefore hard to categorize. This may be a result of other infectious diseases occurring in the same area whose symptoms are diagnosed through microscopic examinations thus missing out on sub-microscopic details of other infections.
Diagnosis of Mansonella perstans
Current studies have indicated that an important Wuchera bancrofti diagnosis assay (the ICT card test), which has been applied more often for World Health Organization lymphatic filariasis identification, can cross-react and result in unexpected positive identification for people from Wuchera bancrofti – free regions. If Mansonella perstans is shown to have a critical responsibility in this cross-reactivity, Mansonella perstans diagnostics that can aid in the parasites’ mapping may a crucial tool for the World Health Organization’s nascent lymphatic filariasis and onchocerciasis depletion strategy.(Alhassan et al. 2014; Wanji et al. 2015). Mansonella perstans parasitism is normally detected by first diagnosing their microfilariae. These microfilariae are normally archived from the circulating blood, but have also been identified and found in the ascetic fluid, pleural effusions, bone marrow, and skin. Polymerase Chain Reaction assays have been improved and shown to be effective for this purpose, however, most identifications of Mansonella perstans has long been done with parasite morphology, using light microscopy and thick blood smears. Mansonella perstans can be differentiated from other blood related nematodes found in Africa by their tiny body size and their tails that are nucleated and by the fact that they are unsheathed (WHO 1997; Muller 2002; Simonsen et al. 2011). To be able to meet the immediate needs of the World Health Organization’s lymphatic filariasis and onchocerciasis depletion program, however, Mansonela perstans identification will likely need to be able to diagnose parasites in localities where long term strategies and anti-helminthic treatment measures are already been initiated. Although various parasite concentrating measures such as membrane filtration and the centrifugation-based Knott technique can be applied together with light microscopy to enhance the sensitivity of Mansonella perstans diagnosis, there are studies showing that such techniques can alter microfilariae and make their diagnostic features challenging to recognize (WHO 1997; Medeiros et al. 2010). PCR-based detection strategies could be used to as an alternative to perform this role. The ribosomal ITS-1 targeting protocol of Tang et al. (2010) makes an appealing option for this as it can identify all other regular human filarial parasites and is greatly sensitive and specific (WHO 1997; Muller 2002; Medeiros et al.2010; Tang et al. 2010; Simonsen et al. 2011).
Treatment of Mansonella pertans
It is one of the species of Mansonella. Up to date, there is no known treatment of this filarial infection that is universally agreed upon to effectively eliminate the presence of microfilariae in the body of the host. Therefore, due to the variation of symptoms of this disease from one endemic area to the other, there are totally different approaches to treatment as well. For instance, a recent trial in Mali to determine whether treatment of Mansonella species that tested positive for Wolbachia with doxycycline could actually eliminate the vectors. It showed however that some infection could actually be eliminated. When similar treatment was conducted in Ghana for Mansonella species that had no Wolbachia endosymbiont bacteria, it was reported to be completely inefficient in depleting mansonella perstans microfilariae from the blood of the infected people. Thus, using doxycycline as a means of treatment seems to clear mansonella perstans in some areas in hosts while it is completely inefficient in other endemic areas. The doxycycline has adverse effects on the adult worms and the fertility of the female worms especially The method of using doxycycline in Wolbachia infested Mansonella perstans parasites with seems appealing with no particular side effects, it is however not universally applicable hence of limited importance.
Traditional methods of treatment can also be used. With Loa loa being a coinfection in Mansonella perstans endemic areas, using traditional anti filarial drugs for the medication in trying to eliminate this infection could cause severe side effects if the patients are not examined for Loa loa infection. On the other hand, in situations where the symptoms of this disease are mild and asymptomatic, it is usually ignored and left untreated and therefore individuals who are non-residents in these endemic areas can easily contact the disease. This either through travelling or dwelling in these areas. The treatment therefore of these non-native acquired diseases usually takes a long period of time using doxycycline and hence incorporated the use of other drugs is required. These can either be albendazole, diethylcarbamazine, thiabendazole, and mebendazole. The use of these drugs has shown the clearance of microfilariae from the blood of patients. The commonly used drugs for treatment amongst them is the mebendazole. The drug is given twice daily at 100mg for 28 days for non-natives type of infection since it causes no side effects compared to the use of diethylcarbamazine and albendazole. It also eliminates the presence of microfilariae from the bloodstream. The effectiveness of these drugs showed double efficiency when used together than separate administration. An example is a combination of diethylcarbamazine with thiabendazole and mebendazole with mebendazole that eliminated the presence of both the microfilariae and adult worms. On the contrary, using ivermectin and albendazole singly or in the combination of the two do not eliminate the microfilariae from the host’s blood.( Muller 2002, Bregani et al, 2006, Akue et al, 2011, Simonsen et al,2011). “Ivermectin is effective against a broad range of nematodes of medical and veterinary importance, including the microfilariae of onchocerciasis and lymphatic filariasis, but single-dose treatment of Mansonella perstans with ivermectin has generally shown little effect on microfilaraemias (Richard-Lenoble et al., 1988, Richard-Lenoble et al., 1989, Schulz-Key et al., 1993, van den Enden et al., 1993, Asio et al., 2009c, Asio et al., 2009d). Studies by Gardon et al. (2002) indicated, however, that ivermectin treatment can have a more pronounced effect if the drug is given repeatedly for a prolonged period of time. Assessment of the long-term impact of community-wide ivermectin treatment for onchocerciasis control has given conflicting results with respect to its effect on concomitant Mansonella perstans infections, with a decrease in microfilaraemia reported from some areas (Kyelem et al., 2003) but not from others (Fischer et al., 1996, Kyelem et al., 2005).”(Paul E. Simonsen, Ambrose W. Onapa: Mansonella perstans filariasis in Africa). “Albendazole had no clear effect on Mansonella perstans microfilariae counts when given as one or few single doses (van den Enden et al., 1992, Asio et al., 2009c, Asio et al., 2009d), but more intensive regimens with this drug reduced and even cleared microfilaraemias (Lipani et al., 1997, Duong et al., 1998). Thiabendazole in one or two dosages were also effective against the Mansonella pertans microfilariae (Bregani et al., 2003b, Bregani et al., 2006), but a broader use of this drug is limited by its relative toxicity. The combination of this albendazole and diethylcarbamazine appeared to be even more effective (Bregani et al., 2007b).”(Paul E. simonsen, Ambrose W. Onapa: Mansonella perstans filariasis in Africa)
Prophylactic strategies in managing Mansonella streptocerca has not been developed since then. It was first tested as an alternative treatment strategy in managing Mansonella streptocerca where it proved to be less effective. With the introduction of Wolbachia treatment using doxycycline, it has constantly provided the functions that could otherwise be performed by prophylactic based measures. The Wolbachia based alternative treatment is however not applicable in countries like Gabon, Ghana, and Uganda. (Muller 2002, Bregani et al, 2006, Akue et al, 2011)
MANSONELLA PERSTANS IN SENEGAL, AFRICA
The aim of this study was to evaluate and examine the prevalence and effects of this neglected infection in a rural area of Senegal and to lay the basis for future studies on the reports and documentation of features and symptoms related to Mansonella perstans infection.
Study site: The Bandafassi study area is situated in the region of Kedougou, eastern Senegal, around the border between Senegal, Mali, and Guinea. It is a member of the Sudano–Guinean savannah ecological zone. The area is endangered in comparison with other common rural areas of Senegal because it is situated distantly from the capital, Dakar (700 km), and it is the country’s worst resourced region in terms of health infrastructure programs. The available roads are in poor conditions, mostly impassable during the wet seasons, which is continuous to half a year. The entirety of the population is rural, with farming, including cereal crops, peanuts, and cotton, as the main backbone of their livelihood. The water is sourced from collective wells and there is no electricity power used in the entire village. The dwellings are majorly huts covered with thatched roofs and in most cases, the compounds have no good hygiene including being void of essential things like toilet facilities. There is only one public health clinic within the area, located in the village of Banadafassi, managed by a public nurse. The nearest hospital is at Tambacounda (250 km from the area).
Prior to this study, all parties involved, including parents or legal guardians of all children, submit written, personal informed consent. The county’s ethics council showed approval of the project (a program of identification of emergent pathogens. (Journal of Mansonella perstans prevalence in rural areas of Senegal)
Specimen collection and examination (blood samples): Conducted interviews and sampling in July and December 2010 in rural settings of Senegalese villages in the Kedougou area. The residents of the villages were involved in a longitudinal expected study to determine malaria infection in school-going children in Senegal, including epidemiological risk, the load of disease, and control measures, and a special activity for the identification of rising pathogens. Medical tests and blood smear were done for each kid (school going children) who had a fever > 37.5°C. For the next program (MALEMAF), 200 μL capillary blood was collected and mixed with anticoagulant for molecular examination. In each study, a specifically designed questionnaire was completed. To determine the dominance in healthy children, transversal sampling was performed. Blood smears were stained with Giemsa and deeply analyzed by microscopy to examine malarial trophozoites and gametocytes and the presence of microfilaria.
“On each slide, 200 oil-immersion fields (∼0.5 μL blood) were studied, and the filarial: leukocyte ratio was measured.” (Journal of Mansonella perstans prevalence in rural areas of Senegal)
Arthropod collection: Insects were collected using a modified Center for Disease and Control light trap as initially stated. In a light notice, the tulle net pockets were swapped with pockets of Terylene cloth, which catches small insects. The arthropods were sampled from about nine villages of Kedougou in April 2013 and April 2014. The traps were stored in different niches, resulting in important differences in their qualitative and quantitative results. In each locality, it was placed two traps, one inside a room whose content was a sleeper to capture endophilic Culicoides species and another outside to catch exophilic Culicoides species.
Morphological identification: Using a stereomicroscope, Culicoides species were distinguished from other insects and categorized into the following subgroups based on wing morphology: schultzei, imicola, magnus, milnei, and other Culicoides.Species charactersistics and identification was possible through microscopic analyses of wing patterns and examination of different body parts (head, legs, and wing). After characterization, the species were kept individually at −80°C for further analysis. (Journal of Mansonella perstans prevalence in rural areas of Senegal)
Statistical analysis: The data were analyzed using Epi Info software, version 18.104.22.168 (Centers for Disease Control and Prevention, Atlanta, GA). The significance level of this analysis was given as P < 0.05. (Journal of Mansonella perstans prevalence in rural areas of Senegal)
Entomological examination: in summary, 1,159 Culicoides species were collected (509 in 2013 and 650 in 2014), the majority being females. Most midges in the villages of Laminia and Banding, taking up a percentage of 66.2% (767/1,159) of the collection. After microscopic examination, 10 species of culicoides was characterised. Culicoides enderleini and Culicoides oxystoma were the most prevalent, with a percentage of approximately 34.1% (395/1,159) and 15.0% (174/1,159), of the trapped species. Culicoides enderleini was fairly distributed in the study area, whereas Culicoides oxystoma was common in Laminia and Samekouta, the two villages next to each other. (Journal of Mansonella perstans prevalence in rural areas of Senegal)
Analysis of blood samples: Samples of blood analysis“Blood sample stains were from 297 species examined and analyzed by the sensitive technique of polymerase chain reaction (PCR) method, from people who were infected and who asked for clinical attention due to medical notices in the regions of interest and 96 blood samples from randomly chosen young kids. The ratio of the genders was 50%, and the age category was from 7 months to 45 years. We identified Mansonella perstans in 29 specimens from the febrile people series; this represents a prevalence of 14.4% (29/201). In the afebrile group series, we found 14 positive representing 15.0% (14/96). The world prevalence of Mansonella perstans in this area was about 14.5% (43/297).”(Journal of Mansonella perstans prevalence in rural areas of Senegal)
Mansonella perstans is greatly spread in this area, with only a few villages having a low dominance. The greatest prevalence was identified in Nathia, Bundukundi, and Baraboye. Overall, although Mansonella perstans was found to be highly prevalent among people older than 29 years (33.3%). No cases were identified in the group of patients younger than 12 months.
This study carried out using samples from the Kedougou region indicated that Mansonella perstans is widely spread in this area in Senegal. This wide epidemiological distribution of microfilaria could be positively linked to the high number of its vector and a high vectorial capacity although the vector of this microfilaria has not been shown to occur in Senegal. Initial studies in other countries showed that biting midges are vectors of Mansonella perstans,but this study did not positively identify Mansonella perstans in 1,129 Culicoides species collected in the same area where the human blood samples were examined. Most villages were situated beside either a waterway or a depression filled with water during the wet season, thus providing conducive conditions for larval lodgings for the vector. Mansonella perstans filariasis was found to affect all categories of the different age groups from the samples analyzed, from school-age children to adults. The fact that the effects are greater among adults gave the picture that the immune response of the body against filariasis was absent as individuals infected in the second year (study results) should have favorable time to acquire antibodies against this parasite. Thus, as indicated in other studies, adults were infected more often as children. The fact that the prevalence is higher among adults also showed that they were more exposed than children, or this may be associated with a collective effect. Except for the village of Samecouta, which was void of this parasite, all other villages showed its existence, suggesting that Mansonella perstans is endemic in this area. Further studies could possibly show if the absence of Mansonelliasis in Samecouta as indicated in this study is real and suggest possible explanations of this occurrence. The Iwol village, at an elevation 440 m higher than Ibel, had a percentage of 25%. This could be explained by the number of samples obtained in Iwol (4).
With the number (1,159) of Culicoides species tested, Mansonella perstans was not found in studied arthropods. Many examined species of Culicoides are considered to be anthropophilic (Culicoides imicola, Culicoides enderleini, Culicoides oxystoma, and Culicoides kingi) in Senegal, and even to be associated with the transfer of Mansonellosis in Africa (Culicoides fulvithorax). All the causative agents called midges were captured in April, a time of the year when the greatest count of microfilaria in human beings blood smears was recognized. This capture, though limited due to various conditions, or even performed in the expected season, limits this study. Systematic screening of Culicoides midges for Mansonella perstans throughout a year would have been preferred. The fact that all Culicoides tested by polymerase chain reaction method was negative may suggest the role of another vector of Mansonella perstans in this area such as Simuliidae, Tabanidae, or Culicidae.
Although Mansonela perstans is highly dominant in some areas in Senegal, it is not related to febrile conditions. Proposed effective polymerase chain reaction specifically for Manosnella perstans gives an opportunity for the examination of these filariae in the blood-stained smears. Further investigations are needed to determine the clinical impact of Mansonella perstans in the entire population and to identify the vectors of this highly prevalent species
The result of the study represented pictorially is as shown below;
Source: Available in the Journal of High prevalence of Mansonella perstans in rural Senegal
Mansonella ozzardi: Mansonella ozzardi belongs to Kindom: Animalia, Phylum: Nematoda, Class: Secernentea, Order: Spirurida, Family: Filariidae, Genus Mansonella and Species are Mansonella ozzardi. Most of the persons infected by this species are asymptomatic while some have a skin rash, lymphadenopathy, arthralgia, fever, headache or pulmonary syndromes. Its main diagnosis is through identification of microfilariae in blood or skin specimen. Serology is useful too in its identification but it’s not definite. “Infections with Mansonella ozzardi do not usually result in significant pathological effects. The microfilariae typically remain in the capillaries of the skin and surrounding dermal tissues where they can cause relatively little harm. Researches are carried out through examining the skin biopsies or samples of the blood and analyzing them for the presence of microfilariae. In serious cases, this nematode can cause serious problems such as severe joint pains, eosinophilia, enlargement of the liver and blockage of inflammation of the lymphatic vessels resulting in conditions such as Bacroftian filariasis and elephantiasis. Vectors of Mansonella ozzardi include both biting midges and blackflies. Some of the species that promote the development of microfilariae to the final infective larvae and are commonly considered to have an indirect role in the transfer of the filarial infection are C.barbosai, C.paraensis, and L.becquarti. After a biting midge has fed on the blood meal of an infected host, microfilariae are carried into the midgut where they can penetrate the midgut wall and make their way to the thoracic muscles within a period of 24 hrs. There they develop into third-stage larvae during the next 6-9 days before moving to the head and mouthparts. The Infective third-stage larvae move to the bite wound when the midge afterward feeds on another host. More often, only a few larvae get the chance to fully develop to the final ineffective later stages in a host insect irrespective of the initial count of microfilariae consumed”(Gary R. Mullen, C. Steven Murphree, In Medical and Veterinary Entomology,(Third Edition),2019)
The biology of Mansonella ozzardi
The three species known to cause Mansonellosis in humans are Mansonella streptocerca which is dominant in Africa, Monsonella perstans that is also common in Africa and Monsonella ozzardi that is prevalent in America and the Caribbean countries. The Monsonella ozzardi appears to naturally affect human beings and not other primates such as chimpanzees, rhesus, and capuchin. The infection with filariae Mansonella ozzardi starts with a bite from an infected vector, either the biting midges or the black flies that transmit the infected third stage larvae onto the skin of the reservoirs. Biting midges are tiny flies that are common and breed along with the coastal areas around the sea. On the other hand, black flies are bigger than biting midges that breed in small water bodies such as seas and rivers. The third stage larvae then go through another molting to develop into an adult worm that is cylindrical in shape. “The females’ measures 32-61mm in length and 0.13-0.16 mm in diameter and the male 24-28 x 0.7-0.8 mm. the presumptions about human beings as the natural host still remain uncertain while examinations on already affected patas monkeys show few numbers of adult warms being identified in subcutaneous tissues and not in the abdominal cavities or mesentery. The microfilariae of Mansonella ozzardi are usually smaller than those of Onchocerca volvulus which measure 186-286 μm in length. Despite all these, sizes of these species may overlap indicating a greater diagnostic hindrance when unsheathed microfilariae are identified in skin biopsies from population affected in Africa where species dwell together”. (Downes BL, Jacobsen KH .A systematic review of the epidemiology of Mansonellosis. Afr J Infect Dis 2010). Therefore the life cycle of Mansonella ozzardi can be summarized in the following paragraph according to the center for disease and control. “During a blood meal, an infected arthropod (midges, genus Culicoides, or blackflies, genus Simulium) introduces a third stage filariae larvae onto the skin of the human host where they penetrate into the bite wound. They develop into adults that reside in the subcutaneous tissues. Adult worms are rarely found in human beings. The size range of the female worms is about 65-81 mm in length and 0.21-0.25mm in diameter but unknown for the male adult worms. Adult worms archived from infected patas monkey through examination and experimentation measured 24-25 in length and 70-80mm in diameter (males) and 32-62 mm in length and 0.13-0.16 mm in diameter (females). An adult produces unsheathed and non-periodic microfilariae that reach a bloodstream. The arthropod feeds on microfilariae during a blood meal. After the consumption, the microfilariae move from the midge’s midgut via the hemocoel to the thoracic muscles of the vector parasite. There the microfilariae grow into first-stage larvae and later on into third-stage infective larvae. The third-stage infective larvae move to the midge’s proboscis and can infect other human beings when the arthropod feeds on a blood meal”. (“https:www.mcdinternational.org/trainings/malaria/filaris/body_filaris_Mansonella ozzardi#life cycle”).
“The species is a cylindrical and bilaterally symmetrical worm with a pseudocode. Its exterior, the cuticle is a protective layer that can withstand the harsh environment in the digestive system of the human reservoir. Mansonella ozzardi and other nematodes have a longitudinal nucleus that runs along the body wall. They also have dorsal, ventral and longitudinal nerve cords connected to these longitudinal muscles. Adult Mansonella ozzardi are long, slender with reduced lips. The adult female species are bigger than their male counterparts, therefore, producing many off springs called microfilariae. The Mansonella ozzardi microfilariae are long, unsheathed and have slender, clear tapered tail called a button hook. The nuclei do not extend to the end of the tail. When stained the presence or absence of the sheath, internal nuclei and organs can all be seen with the organization of these aiding in identification and classification of the distinct infective worm species”.(Hazel Barcela, Introduction to Mansonella species)
The diagrammatic representation of the life cycle of Mansonella ozzardi is from the center for disease control and prevention titled “Laboratory identification of parasitic diseases of public health concern”.
Epidemiology of Mansonella ozzardi
The filarial Mansonella ozzardi species is common mostly in America and the Caribbean islands countries. The infection affects persons that dwell along the coastal areas of these countries affected as these places form the breeding sites of the carrier parasite. “the infection rates among the inhabitants is highly variable ranging from as low as 5% or less in Northern Brazil and some of the Caribbean islands to over 95% among Amerindians in Colombia and Venezuela”.(Paul E Simon Sen, Gary J.Weil, Manson’s Tropical Infectious Diseases, (23rd Edition), 2014). The effects of this filarial infection are therefore high in adult male compared to an adult female in the same age bracket
The epidemiological map of Mansonella ozzardi is as shown below;
Source: Mansellosis current perspective
Clinical features of Mansonella ozzardi
Just like any tropical infectious disease, Mansonella based diseases also have unique and distinctive symptoms associated with them. These symptoms although not universally accepted and agreed on, are still the basis of treatment for these filarial diseases. These symptoms in most cases shared among other filarial infections that occur in the same endemic areas. Therefore, this filarial disease is the mildest infection among the three Mansonella species with a percentage range of 30 to 60% (Carlos Brisola Marcondes: Arthropod based infections). Although in some situations, individuals are severely affected by this filarial infection, there are still no common universal symptoms that specifically describe the clinical characteristics of Mansonella ozzardi. The symptoms associated with this filarial infection include: include coldness in the legs, joint pains, skin eruptions, fever, pruritus, arthralgia, hepatomegaly that is characterized by liver enlargement, headache, rashes, lymphadenopathy which is the swelling of the lymph nodes, adenopathy which is the enlargement of the lymph, edema and pulmonary signs being detected in its hosts. With Mansonella ozzardi eosinophilia is also a regular sign which are still common among other infectious diseases like malaria occurring in these same areas of prevalence. Some distinct symptoms such as corneal lesions scarcely occur has been identified with the pathologies of Mansonella ozzardi. Nonetheless, these signs do not frequently occur in every species that Mansonella ozzardi does occur. Because of this indistinctiveness in the symptoms of Mansonella ozzardi, contrasting reports have been found indicating that some of these symptoms do not actually correspond to Mansonella ozzardi. For instance research in the Brazillian Amazon showed that articular pains, headaches and lymphadenopathy were all great symptoms of Mansonella ozzardi while coldness in the legs was not. Another study conducted in the same area of brazillia amazon showed that coldness in the legs, fever are by great chance positive symptoms of Mandonella ozzardi while headaches and lymphadenopathy are not. The explanation behind it being parasite misdiagnosis due to sub-patent Mansonella ozzardi in Brazillian amazon. (Martins et al, 2010, Vianna et al,2013, Adami et al 2014, Medeiros et al, 2015)
Detection of Mansonella ozzardi
Clinical identification of Mansonella ozzardi parasitism is majorly focused on the presence of microfilariae in the circulating blood and generally done using the light microscopy-based technique. This diagnosis can be done all day long as blood circulation is a continuous process in the body. Blood slide is prepared and light-microscopy can be applied, together with species-definite morphological features and staining to undoubtedly detect Mansonella ozzardi parasitemias. Identification morphologically, the unsheathed microfilariae of Mansonella ozzardi can be differentiated from other microfilariae of other parasites by their anucleate tails and/or alcian blue-staining of their cephalic armature. Micro filarial quantities in the circulating blood can, however, sometimes be of lower levels and density to be detected with a light and simple blood film and so parasite concentrating methods are usually used to enhance the sensitivity of light microscope-based detection. Knott in 1939 described a concentration technique that could be used in the diagnosis of low-density microfilariae in a blood sample. This mainly included the mixing of 5ml of anticoagulated venous blood with 50 ml of 2% formalin in a polystyrene tube and obtaining a microfilariae after the sediment is centrifuged. “Also polycarbonate filtration can be used enabling examination of a relatively large quantity of blood. Anticoagulated blood up to around 10ml is diluted in 0.85% saline solution and filtered through 13 or 25 mm polycarbonate membrane. After this process, it is followed by several rinses with saline solution, the wet membrane is placed on a glass slide held tightly by methanol and stained with Giemsa are examined for the presence of microfilariae under 10-40x magnification”. (Arthropod-borne infections). This method, however, has its own setbacks as it alters the morphological features of the Mansonella ozzardi and hence compromising the results (WHO 1997, Medeiros et al, 2010). The Knott and polycarbonate membrane filter strategies are commonly used to resolve this issue; however, these techniques can alter some morphological features of Mansonella ozzardi microfilariae and compromise identifications (WHO 1997; Medeiros et al. 2010). Nevertheless a dependable and greatly sensitive Polymerase Chain Reaction method of Mansonella ozzardi identification has been acquired and can be used for the reliable identification of Mansonella ozzardi parasites in vector and blood specimens, this technique is still not widely applied (Tang et al. 2010; Medeiros et al. 2015 ). Immunology-based molecular diagnostic tools, like ELISAs, which are rarely used for the study of other filarial parasites like Onchocerca volvulus, are still to be verified for Mansonella ozzardi identifications (Post et al. 2003; Alhassan et al. 2014 Luz et al. 2014). In cases where their co-occurrence of Mansonella ozzardi and other filarial infections such as onchocerciasis, a skin biopsy can be acquired and examined for solely diagnosing Mansonella ozzardi presence. Other methods that can, however, be used in such a case include the use of molecular diagnosis for the presence of microfilariae in the peripheral blood, polymerase chain reaction which is an effective way to distinguish Mansonella ozzardi where it is coinfection with other filarial infection such as Onchocerca volvulus and Mansonella perstans. The currently available diagnostic technique called serology is limited and has not been proven to be effective in the diagnostic of Mansonella ozzardi since it is species-based.
Treatment of Mansonella ozzardi
The transmission of Mansonella ozzardi is through vectors that belong to two families of Dipteral. They are biting midges from genus Culocoides which were found in the Caribbean islands and Mexico and black flies Simulium genus and Diptera Simuliidae were also identified to transmit the filarial disease in central and South America. A less frequent vector involved in the transmission is leptoconops of Diptera ceratopogonidae. In Colombia for instance, several lack flies such as Simulium sanguineum, Simulium amazonium and Simulium argentiscutum are prevalent while the biting midge culicoides sanguineum are dominant in Colombia as well.
Having gone through the stage of diagnosing Mansonella ozzardi in a host, there are methods of treatment that are actually put in place to either suppress the presence of the filarial infection or to completely deplete it. Currently, there are no known cure. The ones being applied are for the purpose of suppression or reducing the infection level of this filarial disease. The use of diethylcarbamazine is the most common mode of treatment for this filarial infection having effect on the diseases and no post treatment effects in patients that have been treated through its administration. For instance the administration of monthly doses of 6mg/kg of diethylcarbamazine citrate for a time of one year had no effects on Mansonella ozzardi while it proved an effective way to deplete Wuchera bancrofti in a mass treatment done in 1980 and 1981 in Trinidad. However, when a daily dosage of 150mg per day by adults of Levamisole drug treatment for a period of 2-3 months indicated a positive effects of reducing the prevalence of this filarial infection in a host.
The current treatment of Mansonella ozzardi involves the use of Ivermectin on a single dose of 0.14-0.2 mg per kilogram of body weight with no clear reports on its effects on the adult worms. This drug seems ineffective in the erosion of adult worms in the host. The presence of microfilariae in the bloodstream of the host has in many cases shown to be greatly suppressed by a single dose of 0.15 mg per kilogram for a period of not less than one year of administration. Also, since when tested indicated the existence of Wolbachia endosymbiont bacteria, it is always a good clinical practice to incorporate doxycycline therapy to eliminate these adult worms though it is a method not yet approved and documented.
Proper examination and cautious measures need to be taken in the event that the filarial infection needs to be treated. Presence of other coinfection such as Loa loa need to be checked and the level of their invasion in the host. In areas in Central America where Loa loa and Mansonella ozzardi co-occur, the presence of Loa loa in patients reported to be infected with Mansonella ozzardi should be checked since the disease Loa loa has a serious reaction to Ivermectin treatment especially when loa loa is of high level in the host.
Other prevention mechanisms such as wearing long-sleeved clothes and pants for individuals living in the Caribbean countries should be encouraged to reduce body exposure to these flies, use of insect repellant to protect uncovered body parts and keeping vegetation around short.
Monsonella streptocerca: It was initially called Dipetalonema streptocerca and it is mainly dormant in the tropical rainforest of Africa from Zaire to Ghana with a small portion of it having been found in western Uganda. Again, this filarial is transmitted from one human host to the next through a small biting fly called the biting midge. The general causes and effects of this infection is skin and lymphatic related. Its distribution on the dermal is mainly on the upper shoulders and chest while those who are affected on the lymph may show serious lymphadenitis. The diagnosis of this infection can be done by finding the effects of the microfilariae on the skin nips as it can be easily be confused by leprosy and granuloma infections. “The agent of Mansonella streptocerca was first identified on the skin in 1922. Adult female and male worms were recognized in 1972. Infective larvae are transmitted to human hosts by bites of infected midges. Over months to years, these larvae develop into white, thread-like adult worms that live in the dermal layer of the skin. In bisexual infections, microfilariae are produced and reside in the upper dermal and collagen layers of the skin” (Amy D.Klion, Thomas B Nutman, In Tropical Diseases (Third Edition), 2011). The filarial Mansonella streptocerca have also been identified in other hosts such as the primates. Despite their commonness, few studies have been undertaken on its epidemiology or few medical trials to control it or for its treatment. As a result, this filarial can also be classified under neglected tropical diseases that needs serious research to properly assess its health-related hazards and to find a definite treatment
“In Uganda, the microfilariae identified in the skin are said to be Onchocerca volvulus as the other filarial worms in the skin Mansonella streptocerca have only been reported in the west and central Africa. For the first time, Mansonella stretocerca was found to be wildly distributed in communities in western Uganda along the Zaire border according to the surveys conducted in 1995. More than 300 persons were involved in the survey and a prevalence of about 60% ranging from 30-80% was found. This, therefore, means that Ugandan laboratories using skin nip for diagnosis of filarial infection have to distinguish between Onchocerca volvulus and Mansonella streptocerca microfilariae since the latter may occur in other places around the country”.(Jonathan T Bamuhiiga, DCCH DCEH MPH). It’s mainly prevalent in the rainforest in the west and central Africa. The diagnosis of the same is through the identification of microfilariae in the skin snips or biopsies. In this identification, serology may be of importance but again not definite
The biology of Mansonella streptocerca
Mansonella streptocerca is a Mansonellosis species of the roundworms belonging to a family of onchocercidae. The summary of its life circle according to the center for disease control and prevention is as shown. “During a blood meal, an infected arthropod (midges, genus Culicoides, or blackflies, genus Simulium) introduces a third-stage filarial larvae onto the skin of the human host where they penetrate into the bite wound. They develop into adults that reside in the subcutaneous tissues. Adult worms are usually small and slender. The size range of the female worms is about 49 mm in length and 150 μm in diameter or 26 mm long and 70 μm wide for the male adult. An adult produces unsheathed and non-periodic microfilariae that reach the bloodstream. The arthropod ingests microfilariae during a blood meal. After ingestion, the microfilariae migrate from the midge’s midgut through the hemocoel to the thoracic muscles of the arthropod. There the microfilariae develop into first-stage larvae and subsequently into third-stage infective larvae. The third stage infective larvae migrate to the midge’s proboscis and can infect another human when the arthropod takes a blood meal”. (www.cdc.gov/parasites/: Laboratory Identification of parasites of public health concern).
“The species has four cephalic papillae arranged dorsally in an elongated rectangle shape and four external labial papillae arranged in a square. The male and female adult worms can be distinguished from each other with the position of vulvas which is reported to occur between 0.4 and 0.54 mm from the anterior end of both primate and human-derived adult Mansonella streptocerca worms. The paired uteri of mansonella streptocerca in females are reported to be straight and run the length of the body from about 2mm from either end. The ovary and ovary ducts are confined to the last 2mm of the posterior end of the worms and join to form a vagina. The female anus is recorded to be between 0.1 and 0.15 mm from the posterior ends of the worms, the tails of mansonella streptocerca females from bonobos are 0.16-0.22 mm. male worms from humans have smooth cuticles and to have morphological features consistent with the adult males obtained from chimpanzees and are reported to be 13 and 18.1 mm in length and to be up to 0.05 mm in width.”(Carlos Brisola(eds): Arthropod-borne diseases)
The tail length of male worms from chimpanzees is 0.067-0.074 mm with the left spicules being o.333-0.349 mm while the right one is 0.117-0.120 mm. The size range of esophagi are recorded as 0.383 -0.90 mm in length while the nerve ring is 0.2- 0.202 mm from the posterior end of the worm. ( Neafie et al, 1975, Meyers et al,1977, Muller 2002, Bain et al,2015)
The following diagram represents the summary of the life cycle of Mansonella streptocerca.
Source courtesy of: www.cdc.gov/parasites
Epidemiology of Mansonella streptocerca
Mansonella streptocerca, on the other hand, is found to be prevalent in the west and central Africa respectively. “A study in western Uganda in the mid-1990s conducted found that the village prevalence ranged from 5% to 89 %”.( fisher et al, 1997). Again another survey done in the Central African Republic found a prevalence of 13.5 % (Okello et al, 1988). Additional surveys in Nigeria also got a dominance of 0.5 % (Anosike and Onwuliri 1994)
The epidemiological distribution on a diagram is as shown below
Source: Mansellosis current perspective
Clinical features of Mansonella streptocerca
While other filarial maladies including Wuchera bancrofti tend to cause common illness to their hosts, the clinical appearance of most of Mansonella infection usually occurs in mild cases with most of them being asymptomatic especially in persons living in areas of dominance. What is more confusing among these filarial Mansonella infections however is that their geographic distribution always appears to overlap those of other filarial illness that show similar symptoms. Therefore it is hard to be sure sometimes that the symptoms shown in some studies in areas of dominance could be a result of Mansonella or infection from other parasites.
Originally the infection was not positively associated with skin infections. However, there are symptoms already established for this infection which are mild. The symptoms are sometimes not manifested by individuals infected. The major clinical features include: pruritus, dermatitis, and hypo pigmented lesions. Also, eosinophilia is a common sign associated with this filarial infection
Diagnosis of Mansonella streptocerca
Mansonella streptocerca is currently identified by the detection of microfilariae extracted from skin biopsies. Those microfilariae can be diagnosed by polymerase chain method or by their morphology and motion analyzed under light microscopic examination (WHO 1997; Fischer et al. 1998; Muller 2002). The diagnosis of this filarial disease can also be done mainly through the identification of the morphological features of the microfilariae on the skin nips. The two main coinfections however are leprosy and granuloma that need to distinguish from Mansonella streptocerca in terms of patient symptoms and mode of treatment to be employed
Treatment of Mansonella streptocerca
Like any other filarial infection, Mansonella streptocerca has also its control and measures put in place to aid in its prevention. The midge that is commonly known to be a causative agent of Mansonella streptocerca also supports the occurrence of this filarial infection. This biting midge is called Culicoides grahamii, the known vector.
The effective method for treatment for this filarial infection is the administration of diethylcarbamazine as it erodes both the microfilariae and adult worms from the host. The daily dosage is 6mg per kilogram body weight for three weeks. Like onchocerciasis infection, this mode of treatment results in urticarial, arthralgia, headaches and abdominal discomfort post-treatment effects. Using ivermectin at a dose of 150 g per kilogram weight leads to salutary microfilariae post-treatment that can only be managed for 12 months beyond which it results in severe health problems. (Thomas B. Nutman, Travel and Tropical Medicine Manual 2008)
Since there are no international program of strategy put in place that targets the treatment of Mansonella streptocerca, the world health organization recommends treatment using ivermectin as this is the only sure way that Mansonella streptocerca can be eliminated. The filarial infection has not also tested positive for Wolbachia that could otherwise be used as an alternative treatment strategy. Doxycycline cannot therefore be administered to Mansonella streptocerca patients as it has been associated with post treatment effects. Diethylcarbamazine and ivermectin are not yet tested to be a possible treatment for the Mansonella streptocerca but both have indicated to be a sufficient and effective method in eliminating the microfilariae from skin nips. However, Ivermectin given in doses of 150 kilograms has shown a possibility of eliminating microfilariae from the dermis of 55% of affected people treated but does not kill adult worms( Carlos B Brisola (eds) Arthropod-borne diseases,2017) hence it cannot be regarded as an effective treatment for the filarial infection. On the other hand, daily doses of 3-6 kilograms of body weight of diethylcarbamazine administered for 28 days daily eliminated microfilariae from the skin and killed adult worms (Meyer et al, 1978, Fistcher et al, 1997; Muller 2002). Although a lot of efforts are made to clear microfilariae, it is not viable since the people affected by Mansonella streptocerca also suffer Onchocerca volvulus and the treatment of the latter always precedes over Mansonella streptocerca. Again these two methods of treatment can cause serious side effects including death when administered to patients with Loa loa. Therefore until today Wolbachia has not been detected in Mansonella streptocerca and whether it can be used as an alternative treatment is still not certain. Hence it is advisable to examine Loa loa in Mansonella stretocerca patients and if there are high levels of invasion then it is advisable to leave the patients untreated.
The following information about the three species of Mansonellosis: adult size, microfilariae characteristics, vector, host, signs can be summarized in the following table
Agent Mansonella perstans Mansonella streptocerca Mansonella ozzardi
Adult size Male:4cm in length by 0.6mm in breadth
Female:7cm in length by 0.12mm in diameter
Male :17-18 mm x 0.4mm
Female :25-27mmx0.6-0.8mm Female :65-81 mm x 0.21-0.25 mm
Micro filarial characteristics Unsheathed
180-240 μm x 5 μm
Unsheathed in size
Tail end is blunt
Nuclei extends to the tail tip 150-200 μm x4.5 μm
Unsheathed and non-periodic
Vector Biting midges Biting midges Biting midges
Hosts Human beings, chimpanzees, gorilla Human are the specific reservoir
Signs and symptoms swellings of the subcutaneous tissues pericarditis
ocular symptoms including blindness and pruritus Edema
Thickening of the skin
Hypo pigmented macules, pruritus and papules Cutaneous itching
Pruritus and articular pains
Subcutaneous inflammation enlarged inguinal lymph nodes
Vague abdominal pains
adult localization Mesenteric tissues
Pleural and pericardial cavities Dermis Connective tissues
microfilariae localization Blood Dermis Blood and skin
Geographical distribution Africa
South America West and central Africa West indies
Central and south America
Pathogeny Generally non pathogenic Non pathogenic Non pathogenic
Diagnosis Microscopic examinations
Antigen detection Finding the characteristics of unsheathed microfilariae in the skin nips Finding the characteristics of unsheathed microfilariae in the blood and also in the skin nips
Treatment No specific chemotherapy Ivermectin
MANSONELLA AND A POTENTIAL NEW SPECIES IN GABON
Like any other tropical African countries, Gabon is infested by various parasitic diseases, including filariases such as loiasis and Mansonellosis. The aim of this study is to explore the dominance of these two filarial infection in febrile and afebrile children using the sensitive quantitative PCR and standard PCR assays combined with sequencing.
DNA from blood samples of 1,418 Gabonese children (1,258 febrile and 160 afebrile) were examined. In general, filarial DNA was identified in 95 (6.7%) children, together with 67 positive for Mansonella perstans (4.7%),that was the most regular Mansonella perstans was identified in 61/1,258 febrile kids participant (4.8%) and 6/160 afebrile participants (3.8%, P = 0.6). It’s widespread increased consistently with age: 3.5%, 7.7% and 10.6% in children aged ≤5, 6–10 and 11–15 years, inclusively. The parasitic nematode, Mansonella perstans widespread was greatl in Koulamoutou and Lastourville (12% and 10.5%, respectively) compared to Franceville and Fougamou (2.6% and 2.4%, respectively). Loa loa was detected in seven febrile children including one co-infection with Mansonella perstans. Lastly, 21 filarial DNA positive were negative for Mansonella perstans and Loa loa, but its sequencing could be demonstrated for 12 and allowed for the potential new species of Mansonella provisionally called “DEUX”. Mansonella species to be found. The potential new Mansonella species “DEUX” was found only in febrile children (Mansonella, including a Potential New Species, as Common Parasites in Children in Gabon)
NB: More researches and study should be conducted and carried out to categorize Mansonella species “DEUX” and examine the clinical importance of Mansonellosis in humans.
About 114 million people in Africa, mostly situated in 33 Sub-Saharan African countries, are infected with Mansonella perstans, a filarial species. The potential of Mansonella perstans to induce serious clinical symptoms has only recently been considered. Nevertheless, no study conducted has analyzed its load in febrile patients in Gabon, a tropical African country where febrile and parasitic infections are widespread. Molecular tools were developed to detect Mansonella perstans and other Mansonella species as well as Loa loa, another filarial disease in blood samples of febrile and afebrile Gabonese young ones. The results suggest that there does not exist any direct association between the species Mansonella perstans and shiver among the local residents (61/1,258 febrile children [4.8%] versus 6/160 afebrile children [3.8%]), while Loa loa and another potential new species Mansonella species “DEUX” was only found in febrile patients (seven and twelve, respectively). Further study should be performed to characterize Mansonella species “DEUX” and evaluate the clinical significance of Mansonellosis in humans
This study is focused mainly on the assessment of the dominance of Mansonellosis and Loa loa, a co-infection in febrile and afebrile children from Gabon employing the molecular method. A febrile is a situation that is not associated with any allergies or fever while febrile is as a result of allergen reaction
Regions of study and populations
This study was conducted in four locations of Gabon situated in three regions of the country: Franceville (Haut-Ogooue province), Koulamoutou and Lastourville (Ogooue Lolo province), and Fougamou (Ngounie province). Among the population of these children, 997 (873 febrile and 124 afebrile) were involved in Franceville, 171 in Lastourville (155 febrile and 16 afebrile), 83 in Fougamou (63 febrile and 20 afebrile), and 167 febrile young kids found in Koulamoutou. All the children were from pediatric outpatient wards of Regional hospital centers (Franceville and Koulamoutou), Medical Center (Lastourville), and Medical Research Unit (Fougamou).Lastly, seven samples of blood from two other locations of West Africa that had initially been identified to be positive for Mansonella perstans were included in the analysis in order to contrast and compare the sequences and construct phylogenetic trees. Two samples were from the Republic of Côte d’Ivoire and five samples were from Senegal.From each one of the children, 100μl of DNA was obtained from 200μl of blood samples (collected in EDTA tubes) using a DNA Blood Kit E.Z.N.A (Omega Bio-Tek, Norcross, U.S.A) in regards to the manufacturer’s guidelines. The DNA was extracted in Franceville, kept at -20°C and sent in ice packs to URMITE, Marseille, France for molecular analysis
Quality controls: Examination of the standard of DNA samples was conducted on each sample using a quantitative definite PCR (qPCR) with its target on the human ß-actin gene. For every PCR assays conducted, a combination of PCR alone was used as a negative control for every ten samples. On the other hand, positive controls (DNA of the targeted parasite), two per assay, were also involved to validate each reaction.
Primers and probes: All samples to be used were first screened with qPCR using the given primers and probe with its focus on the Inter Transgenic Spacer (ITS) that was capable of amplification of all species of Mansonella genus as well as Loa loa. All samples that tested positive for ITS qPCR were sequentially examined with a qPCR focusing on Mansonella perstans as well as a qPCR specifically for Loa loa. Moreover, they were also all magnified with standard PCR assays focusing on ribosomal DNA ITS1 and 5S rRNA areas combined with sequencing. Lastly, a new set of primers and probe were designed to amplify a part of the ITS1 sequence of a potential new species of Mansonella identified in this study.
PCR assays: The CFX96 Touch detection system test (Bio-Rad, Marnes-la-Coquette, France) was employed to perform qPCR. FAST qPCR MasterMix (Eurogentec, Liege, Belgium) was prepared in line with the manufacturer’s protocol and used during this step as initially reported. Standard PCRs were conducted using GeneAmp PCR System 2720 thermal cyclers (Applied Biosystems, Bedford, MA, USA) while sequencing was done with an ABI Prism 3130xl Genetic Analyzer capillary sequencer (Applied Biosystems). Whereas on sequencing, extracted amplicons were cleansed using the PCR filter plate Millipore NucleoFast 96 PCR kit according to the manufacturer protocols (Macherey–Nagel, Düren, Germany). Sequencing results were done using the Big-Dye Terminator, version 1.1, cycle sequencing kit DNA according to the manufacturer’s instructions (Applied Biosystems, Foster City, USA). Lastly, sequencing outcomes were cleansed through the application of Millipore MultiScreen 96-well plates (Merck, Molsheim, France), consisting of 5% Sephadex G-50 (Sigma-Aldrich, L’Isle d’Abeau Chesnes, France). Finally, ChromasPro 1.34 software (Technelysium Pty. Ltd., Tewantin, Australia) was applied to rectify sequences and BLASTn searches were conducted in the NCBI
Phylogenetic trees: Phylogenetic trees indicating the association between the species of filarial nematodes under study were made on the basis of comparisons of the ITS1 and 5S sequences. The resulting sequences were arranged through the application of ClustalW, and phylogenetic citations were made through Bayesian phylogenetic examination with TOPALi 2.5 software inside the distinguished Mr. Bayes application and using the HKY85 substitution model. The values at the apex are percentages of bootstrap numbers obtained by looping the analysis 100 times to generate a majority consensus tree.
Statistical analysis: Epi Info software (Centers for Disease Control and Prevention, Atlanta, GA, USA) was involved to conduct data analysis. Mantel-Haenszel χ2 and Fisher exact tests. The statistical significance was determined for a two-tailed P-value lower than 0.05.
Detected filarial: In general, 95 out of 1,418 samples (6.7%) were positive based on ITS qPCR. 67 (4.7%) were positive for Mansonella perstans and 7 for Loa loa (including 1 co-infection with Mansonella perstans), whereas 21 were negative using these two qPCR tests. Identification of Mansonella perstans and Loa loa was confirmed with sequencing and the BLAST search tool. The children identified with Loa loa were febrile; two were from Franceville, two from Koulamoutou, one from Lastourville, and two from Fougamou
Mansonella perstans is the most prevalent filarial parasite detected in 67 children, including 61 febrile (4.8%, 61/1,258) and 6 afebrile children (3.8%, 6/160; P = 0.6). Overall, Mansonella perstans was detected in 3.5% of children ≤ 5 years of age (36/1,036), 7.7% of six to ten-year-olds (21/272), and 10.6% of 11 to 15 year-olds (7/66),. The prevalence was statistically significantly lower in children ≤ 5 years of age than in those between six and ten-year-old (P = 0.004) and in those between 11 and 15 year-olds (P = 0.01). There was no significant difference in the statistical dominance observed in young kids between ages six and ten and those between 11 and 15 year-olds (P = 0.4). Moreover, no further distinction in Mansonella widespread was reported between males (4.3%, 30/703) and females (4.9%, 33/673 P = 0.6). The prevalence of Mansonella perstans was significantly lower during the dry season (3.9%, 34/864) compared to the wet season (6%, 33/554), but without statistical significance (P = 0.09).
Mansonella species “DEUX”: From the 21 positive specimens positive with ITS qPCR, but negative with Mansonella perstans and Loa loa qPCR assays, sequencing of ITS1 was done for 12 groups; not enough DNA was readily available for 9 samples from Franceville. The sequences were nearly identical to each other (two samples had the same single nucleotide polymorphism) and significantly distinct from sequences of Mansonella perstans: nine nucleotide polymorphisms and five deletions/insertions for the sequenced part (94% of identity). The BLAST search strategy did not result in any identification. However, DNA sequences of Mansonella streptocerca, another possible human pathogen, were not found in the Genbank. The only available gene sequence (5S ribosomal RNA) of Mansonella streptocerca was printed in the manuscript of Fischer et al. So, in order to identify if the Mansonella from 12 samples was Mansonella streptocerca, we sequenced the 5S rRNA of these samples. The comparison of both sequences (the one printed in the manuscript and the one obtained from our samples) showed a difference. This Mansonella species (provisionally called “DEUX”) was identified only in febrile patients. The 12 affected individuals were from Koulamoutou which had four patients, Lastourville also had the same number of patients as well asFougamou.
Nucleotide sequencing: All nucleotide sequences that were extracted during this study were kept in the Genbank under the following numbers: KR080185-KR080190 for the ITS1 sequences from the two genetic variants of the potential new Mansonella species “DEUX” from Gabon, Mansonella perstans from Gabon, Senegal, and Republic of Côte d’Ivoire and for Loa loa from Gabon, altogether; KR080177-KR080184 for the 5S sequences from the two genetic distinct variants of Mansonella species “DEUX” from Gabon, for Loa loa from Gabon, and for Mansonella perstans from Côte d’Ivoire, Gabon and three genetic variants from Senegal, respectively.
Discussion and conclusion
A new potential species of Mansonella was identified on the ground of molecular examination. Amazingly, a Mansonella species that were morphologically distinct from Mansonella ozzardi was recently identified in blood samples from Peru, but no genetic differences were found. It is unfortunate that it was a failure obtaining blood smears, thus, no morphological characteristics and analysis of Mansonella species. “DEUX” was possible. It is critical to put emphasis that Mansonella species “DEUX” was only identified in the febrile young population. There is, therefore, a strong suspicion that Mansonella species “DEUX” may be a new parasite of Mansonella, because according to ITS1 comparison, Mansonella perstans is very uniform throughout Africa (from Senegal to Gabon) and Mansonella species “DEUX” varies greatly from Mansonella perstans with this spacer (94%). From analysis by 5S rRNA sequences, Mansonella species “DEUX” is distinct from Mansonella streptocerca. Distinct variations can also be seen with the following species: Mansonella rodhainii, Mansonella gorillae, Mansonella vanhoofi, Mansonella leopoldi, and Mansonella lopeensis, stated from humans and apes in Africa. However, genes from these nematodes are unavailable in the Genbank. The slides of microfilariae should enable us to deeply describe and analyze morphological features of Mansonella species “DEUX” and to contrast them with the initially mentioned Mansonella streptocerca. Up to now, no other definite species of the genus Mansonella were found in Africa. Hence, Mansonella species “DEUX” may be a potential new species of Mansonella with a possible potential pathogenic role in humans. More morphologic study is needed in order to conclude whether Mansonella species “DEUX” represents one of the Mansonella species not yet molecularly categorized, a genetic variant of Mansonella perstans or really a new species.
Gabon remains an important focus of filariasis including Loa loa, Mansonella perstans, and a potential new nematode of Mansonella, Mansonella species “DEUX”. Mansonella perstans was regularly observed in both febrile and afebrile children whereas Loa loa and Mansonella species “DEUX” were observed only in febrile young kids. Even if Mansonella perstans does not appear to be directly linked to febrile occurrences among the local residents, its real clinical effect has not yet been identified. Additionally, further study should be performed to categoris Mansonella species “DEUX” morphologically and analyze its clinical importance in humans.
Diagnosis of Mansonellosis
Clinical diagnosis: Very few countable clinical features have been largely associated with Mansonellosis generally and currently there is a lot of proofs to support the idea that only Mansonella ozzardi disease cause any clinical signs at all. Thus, it is not proper to make a dependable clinical detection of Mansonellosis, even for Mansonella ozzardi-based Mansonellosis since most of the features that have mathematically great link with Mansonellosis, such as joint pain, are so definite, challenging to score, and are as a result of variety of other pathogens that occur in Mansonellosis dominance regions as to be of almost no use at all. Even the possibility of corneal lesions for clinical identification is deficient, because although they are very perceptible physical signs, they are quite definite, occurring in both infected and uninfected persons from Mansonella ozzardi prevalent locations. Moreover, corneal lesions do not show in every individual who is infected or even occur in every other place that Mansonella ozzardi infests. In summary, it is currently not possible to use the clinical characteristics of Mansonellosis to make detection of the malady.
Immunological diagnosis: Immunological technique involves identification of either antibody or antigen. When a filarial nematode immunodiagnostic assay is detecting antibodies, enhanced specificity is often gotten by assessment of IgG4 rather than total IgG, as IgG4 antibodies are greatly enhanced in microfilaria-positive persons. Currently, there is no effective identifying immunological assay for detecting or epidemiological monitoring of Mansonellosis infections, the equipment has been improved for onchocerciasis and lymphatic infection control measures, and have been examined for cross-reactivity with Mansonellosis sera. The dependability of these immunodiagnostic equipment for lymphatic filariasis and onchocerciasis has not been completely categorized for all of the examinations, and the clearly known and most acceptable examinations are not commonly the most effective, and thus whether they should be applied to aid in Mansonellosis research and diagnosis is uncertain. However, two currently reported Mansonella perstans studies used generic immunological filariasis assays to strengthen the idea of light-microscopy-based diagnoses.
Parasitological diagnosis: Earlier parasitological identifications, which targets the direct observation of a causative agent, is still the most known strategy in which Mansonellosis infections are detected. It is done through the diagnosis and identification of sheath less Mansonella microfilariae in the dermis or blood at any particular time of day or night. Detection of dermal-dwelling microfilariae is normally done by examination of skin-biopsy (skin-snip) samples, extracted with a Walser or Holth corneoscleral punch. The skin-snip needs that a skin biopsy be extracted from areas of already identified optimal microfilariae prevalence, and this fluctuates according to the geographic region. Blood specimens used for Mansonellosis detection are often gotten from peripheral blood specimen by way of finger pricks, although venous blood specimens can also be valuable for this purpose.When microfilariae are in great density in the infected person’s blood, as is often the situation in endemic areas, they may be easily found and detected in thick or thin blood smears stained with Giemsa or hematoxylin. Skin snips are normally incubated in water or saline, and the resulting microfilariae can be stained on microscope slides, but in fresh unstained wet preparations of skin snips, the manner in which the microfilariae moves can also help with their diagnosis. Morphologically, the most important features to analyze in microfilariae in blood smears stained with Giemsa are the body size and shape of the tail, whether it is sheathed or sheathless, and the arrangement of the end of the nuclei. All Mansonella microfilariae are unsheathed, and for identification purposes are treated as aperiodic. The microfilariae of Mansonella perstans are stated to have bluntly rounded tails and to have nuclei up to the tips of their tails. Mansonella. perstans is easily differentiable from other blood-dwelling microfilariae, which have the same distributions (Loa loa or Wuchereria bancrofti), by them being smaller, their lack of sheath, and their tail characteristics (their terminal nuclei are larger than the other microfilariae). Mansonella streptocerca microfilariae are tiny and thinner than Onchocerca volvulus, and are identified with hook-shaped tails with nuclei that lengthen to the end. In moist mounts, live Mansonella streptocerca microfilariae are normally less mobile than those of Ochocerca volvulus. With this morphological characterization, the two filariae should be easily differentiated. Initially, in some nations, such as Uganda, Mansonella streptocerca and Onchocerca volvulus have been confused, even with the clear morphological differences between them. The microfilariae of Mansonella ozzardi are said to have long thin sharp tails and body nuclei that do not lengthen to the end of their tails. As they can reside in both the blood and the dermis, from a public health opinion, it is most crucial that the microfilariae can be distinguished from Wuchera bancrofti and Onchocerca volvulus. The microfilariae of Mansonella ozzardi can be easily differentiated from those of Wuchera bancrofti since they are smaller and have no sheath. Living microfilariae of Mansonella ozzardi can be extracted from skin snips and are not easily distinguished from Onchocerca volvulus by mobility. Their morphology is identical to the pathogenic Onchocerca volvulus, and it is very crucial to differentiate these two species where they are sympatric. Morphological features can be used to differentiate these two nematodes, however, challenges have led to false reports of the currently found onchocerciasis foci and still initiate a problem for onchocerciasis epidemiological mapping in the Amazonia focus, which is currently the Latin America onchocerciasis focus where the transfer is said to be ongoing.
Molecular diagnosis: DNA-based diagnostic tools can be applied to diagnose and identify all of the clearly known human filarial species, however, their most critical use to public health is their potential to differentiate dermal infections of Mansonella streptocerca and Mansonella ozzardi from Oncocerca volvulus skin maladies and Mansonella perstans parasitemias from Loa loa and Wuchera bancrofti parasitemias. DNA-based methodologies for filarial species identification and detection have been proven to be either sensitive or definite, and have now commenced to be an alternative to light-based microscopy in epidemiological studies of Mansonellosis. Molecular identifications may be applied to recognize the microfilariae in both peripheral blood and dermal biopsies, and mature worms in other tissues. Polymerase Chain Reaction based magnification of species of definite sequences enables enhancing diagnostic sensitivity compared to microscopic techniques and dependable distinctions of samples extracted from people living in co-endemic regions. In 2010 for instance, Tang et al improved a popular nested PCR that had the potential to diagnose the life of filariae in the human beings as reservoir. This assay applies universal filariae PCR primers to magnify an inconsistent part of filarial vector ribosomal ITS1 DNA, and enables for the following identification of nematodes according to the size of the magnified portion. This method is applied in conjunction with gel electrophoresis and/or Sanger sequencing, and gives room for the categorization of originally unidentified species. Today, this rDNA ITS1 technique was evolved into a one-step diagnostic by developing it for real-time PCR. This current assay enables for the identification of filarial parasite minus the gel electrophoresis or Sanger sequencing, but does need more resource consuming reagents and infrastructure compared standard PCR assays, and does not allow for the categorization of novel or unexpected filarial species. Other methods (such as PCR–restriction-fragment-length polymorphism [RFLP]) that do not enable the characterization of novel or unexpected filarial species, but needs less systems to support them and can differentiate variety of filarial species using common primers together with Polymerase Chain Reaction, have also been identified. Although it requires less complicated infrastructure system than alternative methods, PCR-RFLP assays still require a link to PCR reagents and a PCR machine, which can be a challenging consideration for filarial carrier epidemiological researches.
Last year, the first DNA-detecting loop-mediated isothermal amplification (LAMP) filarial parasite assays were discovered. Despite all this, these assays have not been thoroughly tested in the field or improved for the identification of Mansonella vectors. There is no reason that is associated with this Mansonellosis research in particular. Requiring almost no infrastructural system, LAMP assays are a specifically interesting for diagnostics choice for research studies that need to be carried out in resource deficient locality. For this, these new LAMP assays can be concluded as a promising discovery for filarial parasite research generally and an appealing news strategy of research to apply for Mansonellosis
Infectious diseases like malaria still pose a lot of challenges and barriers to achieving many sustainable goals. “Malaria still affects millions of people and is the cause of thousands of deaths worldwide, although sub-Saharan Africa pays the highest tribute. (WHO, 2008). Currently, vector control measures are the largest contribution to malaria eradication (Bhatt et al, 2015). If these interventions are maintained or increased, malaria burden would be reduced drastically in Africa before 2030(Griffi et al, 2016). Those predictions are based on the constant effectiveness of these methods. However, the spread of insecticides resistance and vector behavioral changes related to the massive use of bed nets might challenge malaria eradication in the coming decades. Therefore it is vital to develop an alternative and non-pesticide based control strategy for malaria control as it been promoted by the global technical strategy for malaria 2026-2030 which look for reducing global malaria incidence and mortality rates by at least 90% by 2030(Newby et al, WHO,2015)”.(Diego Ayala, Natural Wolbachia infections are common in the major malaria vectors in central Africa)Heavy investment has been made in the effort to control and minimize the effects of these diseases on individuals, the economy, and society in general. Therefore there has been a lot of discoveries on the infection of the endosymbiont bacteria Wolbachia of the malarial mosquito Anopheles gambiae in West African countries such as Burkina Faso and Mali. There is also two malarial vectors in an endemic area in Tanzania: Anopheles arabiensis and anopheles furiestus. “The maternally inherited endosymbiont bacteria Wolbachia infects an estimated 40 to 66% of all insect species worldwide” (Werren JH, Baldo L, Clark ME, Wolbachia: master manipulations of invertebrate biology. Nat Rev Microbiology, 2008). Therefore Wolbachia is a common endosymbiont bacteria that can affect the reproduction of the female reservoir while influencing the pathogen transfer. “wolbachia pipiensis is a naturally occurring bacterial endosymbiont of insects and other invertebrates that has recently gained prominence as a means of biological control of important vector species”.(Carlos Brisola (eds); Arthropod-borne diseases, Springer international publishing, 2017).“Wolbachia has been used or hypothesized for use in a number of different vector control projects in the field. Each of these projects takes advantage of the physiological manipulations that Wolbachia causes in its host. A further benefit, which assists both with facilitating the regulation of the projects and with public opinion, is the fact that control using Wolbachia does not involve transgenic organisms. Although there are differences in format, all of these projects seek to exploit the natural biological relationship between Wolbachia and host, with the aim being to target undesirable vector or pest populations.”((Carlos Brisola (eds); Arthropod-borne diseases, Springer international publishing, 2017).)
There are numerous species of anopheles that possess the ability to transmit malaria infection but Wolbachia have tested positive in all except anopheles genera. The strains of it was however obtained in the following anopheles species: Anopheles coluzzii, anopheles gambiae, anopheles arabiensis, anopheles moucheti, and anopheles species A hence elevating the number of species known to be naturally infected. The prevalence of the bacterium Wolbachia varies from one region to another with these species also varying phylogenetically. The strains, therefore, are in high levels in anopheles moucheti and Anopheles species A but is of low levels in anopheles coluzzi. Wolbachia is a maternally transferred infection from female host to the offspring it has posed serious reproductive health among several insect species. In many situations, it is known to cause cytoplasmic incompatibility, a situation where uninfected female and affected male unable to form a viable offspring. This can eventually lead to Wolbachia infected genes growing faster in the carrier population. This incompatibility is important as bearing genetically incompatible male species can be a good strategy in eliminating pest insect numbers. Also, Wolbachia induced cytoplasmic incompatibility can be used to enhance the spread of symbionts through specific insect numbers hence a means to curb pest numbers and bar the capability of the vector transferring the bacteria to another host.
Wolbachia is a varied bacteria. It can be further divided into several super groups initialized by A-F, H-Q. Among these further divisions and super groups, some strains of Wolbachia indicate a stronger correlation with the reservoirs others affect a variety of hosts. “A naturally occurring Wolbachia strain (wAnga mali) was identified in the Malian villages of Dangassa and Kenieroba. Phylogenetic analysis of the nucleotide sequence of the two 16s and rRNA regions showed that wAnga Mali clusters with Wolbachia strains from super group A and has the highest homology to a Wolbachia strain isolated from cat fleas”.( Fabio Genres, Effects of Natural occurring Wolbachia in Anopheles gambiae SI mosquito from Mali of plasmodium falciparum malaria transmission).
Wolbachia is a bacteria that can be transmitted in two ways, either vertically or horizontally. It is transmitted vertically among the arthropods and horizontally among the human population from mother to the offspring.
Control and prevention strategies are already in place. A lot of measures have been put in place, some of which have borne fruits others are yet to be affected. Despite all these efforts and measures made to reduce the load of malaria in most African countries, the infection still remain a killer and a threat today. Most of the deaths among the infants are caused by anopheles plasmodium falciparum in sub Saharan Africa where the two main vectors are Anopheles gambiae and Anopheles coluzzii. They have been recently classified as distinct species as they dwell in different niches and share no genetic information. Control, however, has been reliant on the insecticide whose efficiency has been of concern as the pests have become pesticide-resistant. Another control has been the treated mosquito nets that are not always available in the remote areas of some countries. With these challenges, there is a need to develop an alternative measure that is non-pesticide to aid in the erosion of these parasites. Among the proposed alternative is the use of maternally inherited Wolbachia that is showing a lot of efficiency and viability. It not only aids in fighting malaria but also other vector-borne diseases. The bacterium shows a wider scope of association with the reservoir from a dual relationship to mutualism. (Werren, Baldo, Clark, 2008). The invasion of these maternally inherited bacterium will hinder the further transmission of malaria through infected pests and the transfer of other vector-borne infections
Biology of Wolbachia
The endosymbiont bacteria is a member of the Rickettsiales. It presents a dual association with the host especially among the arthropods and a mutual one with the nematodes. The maternally inherited bacterium belongs to the class Alpha-proteobacteria, order Rickettsiales and the family of Ricketsiaceae. (Marshall Herrings, Samuel Wolbochia, 1994). This association with the host varies accordingly. The variation, therefore, represents a complex relationship that exists between Wolbachia and the host. Some of this association is mutual in nature, purely parasitic or a combination of the two, a term referred to as ‘Jekyll and Hyde’ infection. (Jiggins and Hurst, 2011). The symbionts that are transmitted vertically from the female adult bacteria tend to have a parasitic relationship with the host or face the threat of elimination. Parasitic relationship results from the bacteria manipulating the reproductive systems of the hosts to facilitate their survival while dangerous to the host. However, since the female species is the one to transmit the Wolbachia bacteria, the infection among male counterparts is insignificant as it does not directly affect the offspring. With evolution and development, it’s known to tamper with the reproductive health of the host of the millions of insects it affects globally. “The endosymbiont Wolbachia manipulate and alter the host reproductive systems (Werren et al, 2008) through various phenotypic mechanisms such as: killing the male sperms during embryonic development where only the female species survive to adulthood (Stevens et al, 2001). This reduces the possible completion of the female species with the male counterparts for survival. Feminization where the bacterium genetically modifies the male host to make it a fully functional female and even forces it to develop into female especially in terrestrial isopods. Next is the cytoplasmic incompatibility between Wolbachia infected male and the uninfected females whenever they mate. The last effect of this reproductive manipulation is the induction of pathogens”. (Habib Ali, Youming, Bozhe Tang: Journal of Experimental Biology and Agricultural Science). “Parthenogenesis occurs when “Wolbachia cause unfertilized eggs that would otherwise develop into males, to develop as females, as seen in Trichogramma wasps. In some parthenogenetic species, such as Franklinothrips vespiformis Wolbachia is required in order to produce female progeny” (Carlos Brisola Marcondes, Arthropod-borne diseases, Springer international publishing, 2017). The bacterium is often associated with eight supergroups, A-H (Zhou et al, 1998). Moreover, according to some surveys conducted, infectious endosymbiont Wolbachia can still be subdivided into three more categories, A-K super groups (Zhoo et al, 1998).
The size range of the bacterium is 0.8 to 1.5 um (Herring et al, 1935 with complete reliance on the endoplasmic environment. Though a lot of its dominance is on the reproductive area, it also has severe effects on the muscle tissues, digestive organs, brains and the hemolymph of the reservoir.
The bacterium like any other can be diagnosed. The diagnosis can be done through various techniques such as visualized Giemsa stain (Herring et al, 1936), fluorescent dye (Albertson et al, 2009). Other methods such as the polymerase chain reaction technique along with hybridization can also be applied in the detection of the bacteria.
Epidemiology of Wolbachia
The bacterium endosymbiont Wolbachia is widely spread and infects many species of insects. They are reported to have been found in many species of insects around 80 species (JH Werren, Unpublished reports). The maternally inherited bacteria if from Alphaproteobacteria class. The species of arthropod infected include: mosquitoes, flies, butterflies, flies, ants, wasps, spiders, scorpions, terrestrial isopods and filarial nematodes. The bacteria affect between 25 to 70% of all insect species but the recent surveys indicate a percentage of about 40%.(Carlos Brisola, arthropod-borne diseases 2017) Due to this greater extent of infection among insects, the bacteria has therefore evolved in both its genetic functions as well as biological functions. For instance, wMel is the strain that affects Drosophila melanogaster. Some of the vectors of certain infections are however not by the strains of Wolbachia. These include the majority of Anopheles vectors that transmit plasmodium (Baldini et al, 2014), dengue, Aedes aegypti and zika mosquitoes. On the other hand, Aedes albopictus and Calex pipiens are infected naturally. The heights of distribution of this bacterium are undisclosed as the infected insect species are quickly multiplying. Other species are also being identified as well. The sensitive technique of polymerase chain reaction has therefore made it easier to carry out an outlined survey of the distribution of Wolbachia with the 16s DNA and ftsZ studies providing good molecular information for such insightful research. This widespread has been found also in terrestrial isopods identified in the seventeen categories of oniscidae.
Treatment of Wolbachia
“Treatment of endosymbiont bacteria Wolbachia using antibiotics is a possible target for anti-filarial practices. Therefore, most recent research looks for new methods of action for novel antibiotics to cure filarial caused infection to fully prevent Wolbachia from reaching antibiotic resistance”.( Boucher, Lefoulon E, Karadijian G; The Symbiontic role of Wolbachia in Onchocercidae and its Impact on Filariasis, Clinical Microbiology and Infection)
“Treatment of 100 mg/day for six weeks indicated full Wolbachia erosion and sterilization of female filarial species for 18 months. 200 mg/day for a period of 4 – 6 weeks showed serious effects towards filarial nematodes. On the contrary, doxycycline can interfere with bone and teeth development, making it unsafe for children and pregnant women to use. Due to its long duration treatments and its incapability to be safe for all people to use, doxycycline is unsuitable for administration. Therefore, other combinations of effective treatments are being evaluated as an alternative to doxycycline.” (Boucher, Lefoulon E, Karadijian G; The Symbiontic role of Wolbachia in Onchocercidae and its Impact on Filariasis, Clinical Microbiology and Infection)
“According to Schiefer et al., treatment of 35 mg/kg/day for 28 days depleted more than 98% of the Wolbachia along with no serious side effects to the mammalian reservoir. These results are equivalent to a treatment of high dose of doxycycline for a shorter period of time and a longer duration treatment of rifampicin. Treatment using Corallopyronin A resulted in shorter larvae and sterility of the female filarial species. These results indicated the possibility of Corallopyronin A as a potential antibiotic for treatment of filarial caused infection”. (Boucher, Lefoulon E, Karadijian G; the Symbiontic role of Wolbachia in Onchocercidae and its Impact on Filariasis, Clinical Microbiology and Infection)
A recent finding in effective antibiotic treatments indicated that there are a lot possibilities for the capability antibiotics. Johnston et al. resorted to repurposing antibiotics. They found that 69 out of 121 compounds that were indicated in their research towards filarial nematodes were observed as possible effective targets for depleting Wolbachia from these species. Therefore according to this finding, 4 out of 15 selected compounds were found in this study. The effectiveness of these compounds was analyzed by weighing their effects to that of doxycycline. These treatments were from the fluoroquinolone, tetracycline, and rifamycin category. One of the most amazing results showed that ciprofloxacin from the fluoroquinolone class showed dangerous effects towards filarial activity. This finding however contradicted initial studies that found ciprofloxacin to be an ineffective treatment for these tropical infections. Hence it is possible that Wolbachia may have lost its antibiotic resistance towards this particular antibiotic and opens up possibilities to new surveys and more treatments that may have been unprioritized to its inconsistencies in eroding the Wolbachia. This specific study has shown that there is much more to learn about this phenomena and much more research to be done to completely understand the details of the symbiotic relationship between host and Wolbachia and possible treatments to interfere with that relationship.
The super groups of the endosymbiont Wolbachia is as shown in the table below:
Super group Host name
C,D Filarial nematodes
F Both arthropods and nematodes
Filarial parasitic worm infections afflict pain in millions of people globally. These infections are not commonly lethal, but the associated morbidities can cause significant physical, psychological and economic suffering for infected people, families, and communities. The prolonged chronic characteristics of infections and propensity for causing irreversible damage further complicates the negative impact of these diseases. Filarial worms of greatest concern to global health are Onchocerca volvulus, the causative agent of onchocerciasis (river blindness), and Wuchereria bancrofti, Brugia malayi and Brugia timori that are the causative agents of lymphatic filariasis (elephantiasis). Most Onchocerca volvulus infections occur in sub-Saharan Africa, with small focal areas of infection occurring in South America and Yemen. In general, 205 million people live in areas where they are vulnerable to becoming infected and about half a million are estimated to be blinded by the disease. Lymphatic filariasis is endemic in an even wider geographic area, found in the tropics of Asia, Africa, the Pacific, and Americas, with 886 million people at risk of infection and 40 million with disfiguring and disabling physical symptoms.( Mansonellosis: current perspective)
Molecular phylogenies examined the origins of the filarial endosymbiont Wolbachia, which infects most filarial vectors including the species of Mansonella. Information from these studies alluded that the filarial parasites had obtained Wolbachia endosymbionts multiple times independently at the time of evolvement of Onchocercidae. These Wolbachia endosymbionts have critical responsibilities in the pathology of onchocerciasis and lymphatic filariasis and are also important for the reproduction and evolution of filarial parasites that cause these infections. This has made them an important focus for therapeutics. Having these complex interactions in mind, it is even more interesting that not all filarial species harbor Wolbachia and that its presence or absence is not consistent within the same genus. When Wolbachia is present, its level of prevalence has been shown to vary between various strains of nematode species and could be associated with different disease severities. Moreover, cases of Wolbachia-free and Wolbachia-carrying individuals of the same species have been studied and challenge the picture of an obligatory interaction. For the purposes of therapy, however, the lack of Wolbachia means that anti rickettsial antibiotics are ineffective. This further shows the necessity of identifying the status of Wolbachia infection, especially in medically important filarial nematodes.
The endosymbiont Wolbachia bacteria that infect Mansonella ozzardi and Mansonella perstans occur to share a common origin but are totally different parasites genetically (belonging to the F super clade of Wolbachia) from the Wolbachia known to cause infection pathologies. It is still not clear today if the information known about other filarial Wolbachia can be safely linked with the Mansonella Wolbachia endosymbionts and if they have a hitherto-unrecognized responsibility in Mansonellosis pathology or actually what their duty in Mansonella-parasite maturity and reproduction is. In 2008, Keiser et al reported the presence of Wolbachia in Mansonella perstans from patients in Mali. This ideology was further supported by a randomized study conducted in Mali, which showed that antibiotic treatment with doxycycline led to a reduction of Mansonella perstans microfilaremia, probably as an effect against Wolbachia. Initially, however, Wolbachia could not be shown to occur in Mansonella perstans from Gabon and Uganda, whereas it had been identified earlier in another Mansonella species infecting human beings, Mansonella ozzardi, prevalent in parts of South and Central America and the Caribbean basin. The reasons for the different reports on the presence or absence of Wolbachia in Mansonella perstans could be ascribed to methodological constraints or might show the existence of different strains of Mansomella perstans in different regions.
However, in some areas where Mansonella persatans occur, such as Gabon and Uganda, Wolbachia endosymbionts have not been identified in the microfilariae of Mansonella perstans. This indicates that some geographic locations isolation of Mansonella perstans may have lost (or gained) the endosymbiont bacteria wolbachia. This presents a controversial argument for the use of doxycycline as a treatment of filarial infections. On one hand, doxycycline has been shown to be one of the only successful treatments for Mansonella perstans, and could facilitate the depletion of filarial parasites. However, some researchers argue that the treatment of filariasis with doxycycline may select worms that will have already integrated Wolbachia genes into their genome, which could potentially have unpredicted consequences. Such lateral gene transmission has occurred in various geographic isolates of Brugia malayi, in which a fraction of the Wolbachia endosymbiont genome is divided into the chromosome of its nematode reservoir (the parasite). When this integration occurs, Wolbachia can no longer be the specific target as a means for treatment for filariasis Mansonella perstans
Nevertheless, in one clinical experiment in Mali, antibiotic as a means of treatment with doxycycline was evaluated to provide effective clearance of Mansonella perstans parasitemias for a period of 12 months post-treatment, suggesting that Wolbachia may have a crucial role in the reproduction and independence of adult worms.
Wolbachia from Mansonella perstans cannot be readily diagnosed, and some Mansonella perstans parasites may not be harboring the endosymbiont bacteria. It has been therefore suggested that Mansonella parasites may have possibly acquired their F-clade Wolbachia (the only Wolbachia super clade found in both arthropod and filarial worm reservoirs) more recently than other filariae, and it may not be a required symbiont for some Mansonella species and strains. In line with this is the idea that Mansonella perstans may be a species complex, and a potential new species or subspecies of Mansonella perstans was recently described from rDNA ITS1 sequences. This possibility of a “new species” was archived from human beings blood samples from Gabon, and has temporarily been called Mansonella species “Deux”.A phylogenetic tree, constructed with Treecon software by the neighbor-joining method, shows that Mansonella species Deux forms a sister clade to standard forms of Mansonella perstans from Brazil and Africa. However, further researches should be performed to categorize this new species and identify its clinical importance in human hosts.
In summary. Infectious diseases are still common and continue to spread widely. Many deaths result from them and therefore continue to pose threats. Talking of Africa for instance where many countries are still developing, some of these diseases may not be of priority considering the quantity of resources required to prevent or contain them. There are a lot of researches made, several surveys conducted on Mansellosis for example and the outcomes shows high prevalence in most African countries. Due to this alarming widespread especially among poor populations living in the remote areas, control and prevention strategies ought to be given precedence.Many questions associated with the biology, transmission, clinical features aspects and public health importance of Mansonella perstans infections cannot be given definite and common answers with the limited knowledge currently available. To show clarification on these issues, there is a need for more research on this prevalent but neglected disease. This includes research on its vectors and epidemiology, on its clinical symptoms (in individuals from endemic areas as well as in visitors to such areas), on the treatment effectiveness of available and new drugs and drug regimens, and on possible tools and strategies for control. Mansonella perstans infections are dominant in rural areas among the poorest of the poor, where variety other infections also thrive and endanger their victims, including HIV, tuberculosis, malaria and other neglected tropical infections. From the present review it is clear that more resources and efforts need to be invested in investigations on Mansonella perstans infections in order to be able to assess with more clarity its health implications on an individual or society in general, and to identify and recommend proper optimal means and strategies for its treatment and control, to the benefit of those affected
Mansonella perstans prevalence in Uganda using actual percentage of occurrence
Source: available in Ann. Tropical Medicine Parasitol page 99
Distribution of Mansonella perstans in the regions of Ghana
Source: Available in the Epidemiology of Mansonella perstans in Ghana
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