EVALUATION OF THE OG4C3 ELISA IN WUCHERERIA-BANCROFTI INFECTION - INFECTED PERSONS WITH UNDETECTABLE OR ULTRA-LOW MICROFILARIAL DENSITIES

The recently developed Og(4)C(3) ELISA, which detects circulating Wuch ereria bancrofti antigen, appears promising for use in epidemiological surveys, but its sensitivity is unknown in persons with ultra-low mic rofilarial densities. We used the Og(4)C(3) to test the sera of 282 pe rsons who were microfilaria-positive in 1-16 ml of blood, Is persons w ho were microfilaria-negative but who had ultrasonographic or biopsy e vidence of adult W. bancrofti infection, and 63 lifelong residents of a non-endemic area of Brazil. A total of 276 (97.9%) persons with dete ctable microfilaraemia tested positive (optical density >0.033). At mi crofilarial densities of <1, 1-30, and >30 microfilariae per ml of blo od, the sensitivity of the Og(4)C(3) was 72.2, 97.6 and 100%, respecti vely (chi(2)-test for trend, P<10(-6)). The assay was positive in 66.7 % of amicrofilaraemic persons with evidence of adult worm infection an d in one (1.6%) of 63 residents of the non-endemic area (specificity, 98.4%) Our findings support the increasingly widespread use of the Og( 4)C(3) for field investigations and epidemiological assessments. Howev er, the sensitivity of the assay may be low in persons who are microfi laria-negative or with densities of <1 microfilaria per ml.