Mansonella Perstans - Diagnostic Tests

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.