Mansonella perstans (formerly Dipetalonema perstans) is a nematode transmitted by Culicoides insects. These midges have an aggressive and very annoying biting behaviour principally at dusk but also to a lesser extent at night and during the day. They bite predominantly on hands, arms and head. They often fly in swarms around the face. In view of their large numbers, they can form a very severe plague. Control is difficult.
The infection is widely distributed in Africa but is more localised in Central and South America. M. perstans does not occur in Asia.
The adult worms live in body cavities (peritoneum, pleura and pericardium) and in perirenal fat. Most patients infected with Mansonella perstans are asymptomatic. A number of different symptoms and allergic reactions are sometimes ascribed to this parasite, but the disease spectrum has not yet been fully established.
The diagnosis is established by detecting the typical small microfilariae in the peripheral blood.
If asymptomatic, no treatment is necessary. A 6-week course of doxycycline with 200 mg/day resulted in a 97% cure-rate at 12 months in a study in Mali. Ivermectin, albendazole and DEC are inactive.