that reach the bloodstream. The microfilariae can also be found in the cerebrospinal fluid. While the periodicity of these midges has been unclear, the most recent study suggests microfilariae indicate a weak but significant diurnal periodicity with a peak around 8 am. 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 midge. In the thoracic muscles, the microfilariae develop into second-stage larvae. They subsequently develop into third-stage larvae, which are infective. The third-stage larvae migrate to the midge's proboscis, where they can infect another human when the midge takes a blood meal. Diagnostic tests Similar to other filarial parasites, M. perstans is diagnosed by the identification of microfilariae in the peripheral blood. Because the microfilariae are present in the peripheral blood in almost equal concentrations during day and night, blood samples can be obtained at any time (unlike other filarial microfilariae). The microfilariae are short and thin, unsheathed, and have rounded tails with nuclei at the extremity. The head spot sometimes has a V-shaped appearance. The blood sample can be a thick smear, stained with Giemsa or hematoxylin and eosin. For increased sensitivity, concentration techniques can be used. These include centrifugation of the blood sample lysed in 2% formalin (Knott's technique), or filtration through a Nucleopore® membrane. Serology is not very useful for diagnosis. Because the adult worms live mainly in pleural and peritoneal cavities, they are only rarely observed. At times, they can be observed during a laparotomy. M. perstans often occurs with other filarial infections, such as onchocerciasis and lymphatic filariasis. It should be distinguished from Microfilaria semiclarum (a parasite of animals which sometimes causes accidental infections in humans). Sometimes, confusion is possible if the blood smear is randomly infected during or after preparation with a mould such as Helicospora. This organism, however, is considerably smaller and thinner than a microfilaria. The DEC, or Mazzotti test, has been shown to have minor effects on microfilariae intensity, but it is not of practical use for diagnosis of mansonelliasis. Management and treatment M. perstans is one of the most difficult human filarial infections to treat. Effective treatment for mansonelliasis is lacking, with no consensus among the scientific community on the optimal approach. Numerous trials evaluating traditional antifilarial drugs such as ivermectin and DEC, as well as other benzimidazoles such as mebendazole, albendazole, levamisole,