Mansonella perstans is a vector-borne parasite; transmitted by tiny female bloodsucking insects of the genus Culicoides (biting midges). It is more prevalent in Sub-Saharan Africa. Most antifilarial drugs including ivermectin and DEC, and also benzimidazoles such as mebendazole, albendazole, levamisole, and thiabendazole, have proven ineffective against M. perstans. Therefore, this study was undertaken to assess the efficacy of doxycycline against M. perstans in the Asante Akim North District of Ghana. The study was an open randomized trial conducted in 8 communities of the Asante Akim North District. Out of a total of 1,229 individuals microscopically screened, 405 individuals were microfilaria-positive representing an overall prevalence of 33.0%. There was no significant difference (p = 0.0568) between prevalence among males and females. Based on the findings from the initial blood samples, 102 eligible individuals were randomized to Early and Delayed groups. Individuals received 200mg of doxycycline daily for 6 weeks. The former group started medication at the initial stage while treatment was delayed for 6 months in the latter group. Five individuals who were not available during treatment, served as controls. Blood samples were taken and analyzed for microfilaria at 4 and 12 months of the study period. There was no significant difference (p=0.7655) between treatment groups at baseline level. Microfilarial load reduced marginally at 4 months even though there was no significant difference (p = 0.5559) between the two treatment groups. However, at 12 months, the efficacy of doxycycline was evident. The Early group had a drastic reduction of microfilarial load resulting in significant difference between the two groups (p < 0.0001). The distribution of microfilarial load among the controls throughout the study time points was relatively constant. A total of 10 individuals reported mild adverse events that resolved spontaneously. A well-designed specific real-time quantitative polymerase chain reaction (qPCR) was used to confirm M. perstans in the blood. Although PCR is arguably very sensitive, microscopy still remains reliable in the detection of M. perstans.

1.1 Background
Mansonella perstans is a vector-borne parasite, transmitted by tiny female bloodsucking insects (biting midges) belonging to the genus Culicoides (Sharp, 1927). It is part of the nematode superfamily filaroidea, which is distributed in parts of South and Central America and Africa. It is prevalent in Sub-Saharan Africa with estimated 100 million people living with the infection (Simonsen et al., 2011).The prevalence of this nematode is high in endemic localities with children also being affected (Stoll, 1947). Four species of filariasis-causing nematodes belonging to the genus Mansonella are responsible for human mansonellosis, M. perstans, M. streptocerca, M. ozzardi, and M. rodhaini (Bregani et al., 2007a). Infections of M. perstans are considered asymptomatic with mild clinical features such as fever, headache, body itches, abdominal pains and eosinophilia (Bregani et al., 2007a).

Sharp (1927) identified Culicoides grahami as a potential vector of the transmission of the infection. Studies conducted in Cameroon have described C. grahami, C. austeni, and C. ornatipennis as potential vectors (Sharp, 1927, 1928; Hopkins & Nicholas, 1952). Further studies were conducted in different countries to search for vectors of this parasite in endemic areas, including Congo (Noireau et al., 1990), Nigeria (Agbolade et al., 2006) and Zimbabwe (Clarke et al., 1971). In East Africa, the taxonomy of Culicoides has been investigated by Khamala & Kettle in 1971). They were able to identify 61 species that had no local role in the transmission of M. perstans.

Humans become infected when bitten by insect vectors carrying the L3 infective larvae (CDC, 2016). In human filariae such as Wuchereria bancrofti and Onchocerca volvulus, there is the possibility of the body’s temperature triggering the larvae to leave the insect vector, thereby forcibly penetrating the skin (Simonsen et al., 2011). In man, the time period for development of L3 larvae into adult stage is unknown. Adult M. perstans are difficult to be identified since they are located in serous cavities of the abdomen, lung and heart. They are sometimes recovered during surgery or autopsy.

Eberhard and Orihel (1984) and Baird et al. (1987) provided detailed morphological information of the adult worm. They are usually slender in shape. The size of the females ranges 50 80 mm×80 120um and the males 35 45 mm×50 60 um. Male and female

adults nematodes are usually white, thread-like and cylindrical which reside in serous body cavities most commonly pleural and retroperitoneal and mesentery. Unlike other adult filarial nematodes such as Onchocerca volvulus which survives for 10 years (Habbema et al., 1990), the longevity of the M. perstans adults remains unknown. The females are viviparous producing about 3000 tiny larvae known as microfilariae (mf), which are unsheathed and possess blunt tails with nuclei extending to the tip of tail. Microfilariae circulating in the peripheral blood can live for approximately 4 months until ingested by vectors during blood meal (Asio et al., 2009a). The parasite could be transferred to a new host after undergoing further growth in the insect vector.

Detection of microfilariae in the peripheral blood (Giemsa staining of thin blood smears) forms the basis for diagnosis of M. perstans infection in endemic regions (Simonsen et al., 2011). This method is relatively time consuming and needs experienced personnel for examination, in order not to confuse diagnosis of mf of M. perstans with those of other filarial species.

M. perstans has been shown to destabilize immunity against Malaria (Metenou et al., 2009). Wammes et al. (2010) observed that children with current helminth infestations respond poorly to vaccination (BCG) or malaria. And this was independent of the type of worm infection. It is therefore important to identify appropriate remedy against M. perstans infections in order to overcome the clinical consequences associated with it.

M. perstans remains one of the filarial infections difficult to manage. Clinical trials investigating the effect of antifilarial drugs such as diethylcarbamazine (DEC) and ivermectin, including other anthelmintics (albendazole, levamizole, mebendazole and thiabendazole) have been reported (Strohschneider, 1953; Richard-Lenoble et al., 1985; Bernberg et al.,1979; Van den Enden et al., 1992). Most of these trials involved a small number of participants, including expatriates and participants harbouring other filarial infections, and were performed within short follow-up periods without clear-detailed analysis of outcomes (Strohschneider, 1953; Adolph et al., 1962). Hence, the outcomes are usually not credible. Effects of treatment have often been analyzed on blood microfilariae and in clinical cases, depletion or elimination of microfilaraemia was in association with amelioration of medical features of the infection in patients.

Diethylcarbamazine (DEC) was introduced as an efficient microfilaricide in onchocerciasis and lymphatic filariasis in 1940. However, investigation by Strohschneider (1953) on its activities on M. perstans revealed that it only brought about little and temporary loss of the microfilariae from patients’ blood. On the contrary, Strohschneider (1953) and Adolph et al. (1962) who treated patients in Uganda and expatriates returning in the USA respectively noted that DEC eliminated microfilariae in large number of patients. Based on carefully performed study, DEC has been shown to reduce M. perstans microfilariae intensities substantially (Bregani et al., 2006) but does not clear them all. In 1975, Maertens and Wery observed significant reduction of microfilariae intensities when combination of mebendazole and levamizole were administered in high doses for long periods to onchocerciasis patients in Congo. Similar outcomes have been documented by Bernberg et al. (1979) and Richard-Lenoble et al. (1985) in Gabon. Wahlgren (1982) and Wahlgren and Frolov (1983) also observed similar outcomes working with expatriates returning to Sweden and in Zimbabwe by Goldsmid and Rogers (1979).

Currently, intensive regimen of mebendazole is generally the preferred intervention against M. perstans infections (Bregani et al., 2006). However, the regimens are cumbersome to administer and not suitable for large-scale field use because of the many doses required. Administering DEC and mebendazole in combination treatment resulted in greater significant effect compared to the single use of either of the drugs (Bregani et al., 2006).

Albendazole was ineffective against M. perstans microfilariae assessment when given as few single doses (van den Enden et al., 1992; Asio et al., 2009b, 2009c), while higher regimens decreased and even eliminated microfilaraemia (Lipani et al., 1997; Duong et al., 1998). One or two dosages of thiabendazole were also active against the microfilariae of M. perstans, but prolonged usage of this drug was restricted by its relative toxicity (Bregani et al., 2003, 2006).

Ivermectin is one antifilarial drug that is efficient in eradicating a wide variety of nematodes that are of veterinary and medical importance, including the microfilariae of lymphatic filariasis and onchocerciasis (Bregani et al., 2006). However, treatment of M. perstans with single dose of ivermectin usually shows minor impact on microfilaraemias (Richard-Lenoble et al., 1988, 1989; Schulz-Key et al., 1993; van den Enden et al., 1993; Asio et al., 2009b, 2009c). Investigation by Gardon et al. (2002) has shown that treatment of patients with ivermectin could result in severe complications if drug is repeatedly given for a longer period. Assessment of treatment with ivermectin for a long term among communities for the management of onchocerciasis has shown contradictory results in relation to its effect on concomitant M. perstans infections, by a reduction in microfilariae counts described in several places (Fischer et al., 1996; Kyelem et al., 2005).

Combination therapy involving albendazole (400 mg) and ivermectin (150-200ug / kg) is encouraged and currently being used in many communities by many programs against filariasis in several African countries (Asio et al., 2009b). Similar doses of drugs on M. perstans microfilaraemia have been extensively evaluated in Uganda in a double-blind study (Asio et al., 2009b, 2009c). No serious adverse events were noticed with marginal reduction in microfilariae levels that were too low and could not result in microfilariae elimination in the follow-up period of 1 year. The lack of adverse events side effects was consistent with previous study by Keiser et al.(2003), proposing that combining albendazole and ivermectin in therapy was fairly harmless for controlling lymphatic filariasis within areas co-endemic with M. perstans infection.

The activities of doxycycline in the life of worms that host the intracellualar endosymbiotic Wolbachia have been clearly identified. It interferes with the development, fertility and embryogenesis of worms (Hoerauf et al., 2003; Debrah et al., 2006). Wolbachiae are endosymbiotic bacterial of insects as well as various filarial nematodes including Brugia malayi, Wuchereria bancrofti and Onchocerca volvulus (Hoerauf & Pfarr, 2007). Although, endobacteria Wolbachia were not identified in M. perstans’ microfilariae in many areas of Uganda (B├╝ttner et al., 2003) and Gabon (Grobusch et al., 2003), the recent discovery of Wolbachia endosymbionts of M. perstans in Mali (Coulibaly et al., 2009) paved the way for more extensive research to be conducted with regard to the use of doxycycline as a chemotherapeutic approach to M. perstans infections.

The treatment of M. perstans infection still remains uncertain since an effective chemotherapeutic intervention is lacking. The optimal remedy of the infection is still being investigated by researchers.

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