Comparative analysis of two diagnostic methods of human loaiosis: IgG4 serology and nested-PCR assay.

By evaluating the diagnostic methods developed in our laboratory the preval ence of loaiosis was estimated among 201 individuals from the province of H aut Ogooue in Gabon using IgG4 serology and nested-PCR. The study showed th at the prevalence of loaiosis was higher than that described using standard microscopy. IgG4-based ELISA (Enzyme Linked Immunosorbant Assay) using cru de extract of Loa loa microfilariae showed that 80% (35/44) of microfilarae mic individuals (MF') and 56% (88/157) of amicrofilaraemics (AMF) presented antibodies. By contrast, L. loa specific DNA amplified by nested-PCR was d etected in all MF and in 68% (106/157) of AMF: Among the 201 samples tested , 95 (47%) gave positive results in both tests. These results indicate that the presence of IgG4 antibodies directed against crude extract of L. loa m icrofilariae is not linked to the positivity of nested-PCR assay (chi(2) fo r paired data = 8.78, P < 0,02). We conclude that the PCR assay is more sen sitive than the detection of IgG4 antibodies (directed against crude extrac t of L. loa microfilariae) in detecting loaiosis, and particularly occult l oaiosis (infection without circulating microfilariae).