DIG-ELISA test in onchocerciasis. Serum antibodies and probability of infection

An immunoenzymatic test (DIG-ELISA) was serologically evaluated for the serodiagnosis of onchocerciasis. Control and infected sera from the onchocerciasis endemic area of Mexico was collected and the donors assessed for onchocerciasis according to parasitological, clinical, and epidemiological data. The sera were submitted to the DIG-ELISA test using a crude extract prepared from O. volvulus adult worms which had been preserved in nodules in 67% glycerol. The test showed a 100% sensitivity with sera from 38 microfilariae carriers and 96% specificity with sera from 133 non-infected people living outside the endemic zone. In addition, seropositivity was 52.9% with samples from non-onchocercotic people living inside the endemic area, while 82.5 and 90.5% of sera from patients with clinical symptoms and subcutaneous nodules, respectively, were positive. A high rate (30%) of cross-reactivity with serum samples from people infected with Wuchereria bancrofti or Brugia timori was obtained, which is in contrast with the low seropositivity rates (7.4%) obtained with sera from patients infected with other parasites. These results suggest that DIG-ELISA test may be a useful serological test for antibody detection in onchocerciasis, especially for epidemiological surveillance of disease, but because of the high cross-reactivity observed, its use must be limited to areas where this parasitic infection does not coexist with other human filariasis. Finally, the arrangement of sera in groups according to the relative likelihood to have onchocerciasis seems to be a useful procedure for evaluation of serological tests.