Three species of Mansonella cause human infections: M. streptocerca, M. perstans, and M. ozzardi. Each species has a limited geographic distribution and typically causes mild symptoms if any at all.
The epidemiology, clinical features, diagnosis, and treatment of Mansonella infections will be reviewed here (table 1A-B). Other filarial infections, including loiasis, onchocerciasis, and lymphatic filariasis, are discussed separately. (See "Onchocerciasis" and "Epidemiology, pathogenesis, and clinical manifestations of lymphatic filariasis" and "Diagnosis, treatment and prevention of lymphatic filariasis" and "Loiasis (Loa loa infection)".)
Epidemiology — M. perstans is endemic in a large portion of sub-Saharan Africa, from Senegal to Uganda and south to Zimbabwe, and in Central and South America from Panama to Argentina (figure 1) . Since the majority of infected individuals are asymptomatic, the epidemiology of M. perstans has not been clearly defined. Nevertheless, it has been estimated that 114 million people may be infected and as many as 581 million people in 33 countries at risk for M. perstans infection in Africa alone .
In endemic regions, the probability of infection increases with age with prevalences reaching 100 percent in highly endemic areas. Infection of travelers is uncommon, but it does occur . Nonhuman primates are occasionally infected, but they do not appear to be a major reservoir of infection.
M. perstans is transmitted by biting midges (Culicoides). The lifecycle is similar to that of other filariae (figure 2). Infective larvae introduced during the bite of an infected midge mature over months into adult worms. The adult worms live in the pleural, pericardial, and peritoneal cavities, as well as the mesenteric, perirenal, and retroperitoneal tissues, where they produce unsheathed microfilariae that are found in the bloodstream at all times. Microfilariae are responsible for transmission of infection because they are taken up during the blood meal of the insect vector. The life cycle is completed following maturation of microfilariae into infective third-stage larvae within the midge. The lifespan of the adult worms is unknown, although microfilaria-positive cases have been reported up to 10 years after the infected individual has left the endemic area .