NOVEL, SENSITIVE AND LOW-COST DIAGNOSTIC-TESTS FOR RIVER-BLINDNESS - DETECTION OF SPECIFIC ANTIGENS IN TEARS, URINE AND DERMAL FLUID

Sensitive, specific and low-cost diagnostic tests for onchocerciasis a re indispensable for monitoring the efficacy of control programs, as w ell as for preventing blindness (when the tests are combined with effi cacious chemotherapy. Three new tests to detect Onchocerca-specific an tigens in tears, dermal fluid and urine employ antibodies to O. volvul us-specific recombinant proteins, Oncho-C27 and OvD3B, encoded by gene s within the immunodominant Onchocerca OV 33-3 gene family, and expres sed in yeast and in E. coli, respectively. In these assays, Onchocerca -specific antigens in test samples are bound onto a solid surface and revealed using appropriate enzyme-labelled antibodies. Proteins in the samples are first transferred to Hybond-N + membrane disks or nitroce llulose paper using either a transblot or a dotblot machine, and then reacted with specific O. volvulus antibodies. Bound antibodies are rev ealed with species-specific peroxidase-labelled antibodies and peroxid ase substrate. Positive tests give a brown colour. In one of the two a ssays developed to detect Onchocerca antigens in fears, the sensitivit y was enhanced by first adsorbing the specific antibodies onto the mem brane surface in order to immobilize and concentrate the Onchocerca-sp ecific antigen molecules on the membrane. The specificity of the recom binant proteins for Onchocerca volvulus had been verified by ELISA, cl assical Western blot and modified DSIA. The tests are a dipstick immun obinding assay for ocular microfilariae (DSIA), a transblot immunobind ing assay for the detection of skin microfilariae (TADA) and a dot-blo t immunobinding assay for detecting urinary microfilariae and their, a ntigens (DIA). Their specificity and sensitivity were evaluated in the field on 110 subjects with proven ocular microfilariae, 130 subjects with clinical and parasitological evidence of onchocerciasis, 25 subje cts infected with other helminths and 120 normal controls. The minimal detection limits of Oncho-C27 protein by DSIA, TADA and DIA were 500 ng/ml, 154 ng/ml and 508 ng/ml, respectively. By contrast, their sensi tivities were: 100% for DSIA and 82.5% for TADA employed on samples of tears; 97% for TADA skin test and 96% for DIA used on urine samples.