Filarial antigen, antibody and circulating immune complexed antigen levels in Bancroftian filariasis by stick ELISA.

Filarial antigen, antibody and circulating immune complexed antigen (CIC-Ag) profiles were studied by stick ELISA in the sera of patients who were in different stages of Bancroftian filarial infection. The geometric mean titres (GMT), of filarial IgG antibody in patients with microfilaraemia (424) and all three grades of clinical filariasis (1485, 3845 and 40216 for grades I, II and III respectively), were significantly higher than in normal controls from endemic areas (47). If a filarial antibody titre of greater than 300 is considered positive, the sera of 94% of patients with microfilaraemia and all those with clinical filariasis were positive. The sera of only 11% of normal subjects from endemic areas and none from non-endemic areas were positive for filarial antibody. The antibody titres were significantly higher in patients with grades II and III clinical filariasis than in those with grade I clinical filariasis or microfilaraemia. Analysis of sera for filarial antigen by inhibition ELISA showed higher GMTs in patients with microfilaraemia (5778) and grades I (3917) and II (676) clinical filariasis compared to grade III (66) clinical filariasis or normal subjects from endemic areas (57). Thus 81% of patients with microfilaraemia, 85% with grade I, 88% with grade II and 20% with grade III clinical filariasis and none of the normal subjects from either endemic or non-endemic areas had a filarial antigen titre of greater than 300. CIC-Ag was found to be present in 8% of patients with grade I, 21% with grade II and 79% with grade III clinical filariasis and in none of those with microfilaraemia or normal controls. While the detection of filarial antibody is useful for diagnosing. microfilaraemia and clinical filariasis, the detection of filarial antigen may be superior for diagnosis of microfilaraemia and grade I clinical filarial infection. Assay of CIC-Ag is useful for diagnosing a grade III clinical infection in the absence of microfilariae in the blood.