EVALUATION OF ONCHOCERCA-VOLVULUS-SPECIFIC IGG4 SUBCLASS SEROLOGY AS AN INDEX OF ONCHOCERCIASIS TRANSMISSION POTENTIAL OF 3 GABONESE VILLAGES

The major objective of this study was to evaluate the usefulness of Ig G4 ELISA and Western blot analysis, using a crude extract of Onchocerc a volvulus adult worms as antigens, for diagnosing onchocerciasis in a Gabonese paediatric population with mixed filarial infections. The su bjects had loaisis, streptocercosis or mansonellosis in addition to on chocerciasis. Control sera from loaisis or mansonellosis subjects resi ding outside the endemic zone were used to provide the cut-off point f or positive results. The IgG4 ELISA had a specificity of 96% but a low er sensitivity of 78.7%. It detected 25 onchocerciasis cases out of 65 individuals who were negative on parasitological examination. Further more, the ELISA provided a more accurate picture of onchocerciasis tra nsmission in a village with very low skin microfilarial load. A.27.5-k D antigen was identified on Western blots as a marker of onchocerciasi s. The paediatric population provided a reliable window for assessing the parasitologic and serologic parameters in the three villages with disparate levels of onchocerciasis transmission.