Loa loa filariasis (also loiasis, Calabar swellings and African eyeworm) is a skin and eye disease caused by the nematode worm, loa loa filaria. Humans contract this disease through the bite of a horsefly. The Deer fly and the Mango fly are also vectors for Loa loa. The disease can cause red itchy swellings below the skin called "Calabar swellings". The disease is treated with the drug diethylcarbamazine (DEC).
Identification of microfilariae by microscopic examination is the most practical diagnostic procedure. Examination of blood samples will allow identification of microfilariae of Loa loa. It is important to time the blood collection with the known periodicity of the microfilariae. The blood sample can be a thick smear, stained with Giemsa or hematoxylin and eosin (see staining (biology)). For increased sensitivity, concentration techniques can be used. These include centrifugation of the blood sample lyzed in 2% formalin (Knott's technique), or filtration through a Nucleopore membrane. Antigen detection using an immunoassay for circulating filarial antigens constitutes a useful diagnostic approach, because microfilaremia can be low and variable. Identification of adult worms is possible from tissue samples collected during subcutaneous biopsies or worm removal from the eye. Antibody detection is of limited value. Substantial antigenic cross reactivity exists between filaria and other helminths, and a positive serologic test does not distinguish between past and current infection.