Analysis of IgG isotype responses against Onchocerca volvulus antigens in children in an onchocerciasis-endemic area in northern Nigeria

Summary This study evaluated the usefulness of parasite-specific IgG and IgG isotype responses for diagnosing early or pre-patent onchocerciasis in children using sandwich ELISA. The children (n = 199) were aged between 5 and 12 years and living in a meso-endemic area of northern Nigeria. Only five had detectable skin microfilariae. The mean optical density (OD) values of children from the study area were significantly higher than those of normal controls' sera (n = 10, p <0.01), except for IgG2. There were 145 (73%) children positive for total IgG, 161 (81%) for IgG1, 68 (34%) for IgG3 and 187 (94%) for IgG4 antibodies. The mean OD values of all antibodies tended to increase with age and peaked in the 9-10-year age group, except in the case of IgG3 which peaked at 11-12 years. IgG4 proved most sensitive compared with IgG, IgG1 and IgG3 in all age groups, and was significantly different (p < 0.05). Analysis by sex showed no significant difference between the boys and girls. We conclude that IgG4 serology is a useful diagnostic tool in the assay of early or pre-patent onchocerciasis in children.