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Mansonella perstans is one of the eight parasitic nematode (roundworm) species that account for most cases of filariasis in humans, although it is responsible for less morbidity than are many of the other seven species (notably, Wuchereria bancrofti and Brugia malayi, which cause lymphatic filariasis, and Onchocerca volvulus, which causes onchocerciasis (river blindness)). Mansonella perstans occurs in both Africa and South America. (Centers for Disease Control Parasites and Health website). It is found primarily throughout sub-Saharan Africa and in northern South America and the Caribbean islands (Hoerauf 2009).
During a blood meal, an infected Culicoides midge introduces third-stage filarial larvae of M. perstans onto the skin of a human host, where they penetrate into the bite wound. They develop into adults that reside in body cavities, most commonly the peritoneal cavity or pleural cavity, but less frequently in the pericardium. The size range for female worms is 70 to 80 mm in length and 120 μm in diameter; males measure approximately 45 mm by 60 μm. Adults produce unsheathed and subperiodic microfilariae, measuring 200 by 4.5 μm, that reach the blood stream. A midge 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 midge takes a blood meal. (Centers for Disease Control Parasites and Health website)