Humoral immune responses in human onchocerciasis: detection of serum antibodies in early infections.

Sera of children (aged 1-15 years) living in a hyperendemic onchocerciasis area (Mali) were tested for antibodies by an enzyme-linked immunosorbent assay (ELISA) and a radioallergosorbent test (RAST), with an extract of adult Onchocerca volvulus as antigen. Serological results were related to age (equivalent to time of residence in the endemic area) and to parasitological findings (detection of skin microfilariae). This longitudinal study (over three years) allowed us to follow early antibody responses in exposed children with no parasitological or clinical evidence of infection and in children who became microfilaria-positive. Serum antibodies against O. volvulus could be detected one to three years before skin microfilariae. RAST, which detected circulating immunoglobulin E (IgE) antibodies, was more sensitive than ELISA in prepatent infections and gave more positive results for exposed but parasitologically negative individuals than did ELISA. During patent infection, IgE antibody levels tended to decrease in about half those infected, whereas in most children non-IgE antibodies showed no significant changes.