RIFT-VALLEY FEVER IN NIGERIA - INFECTIONS IN HUMANS

Between 1985 and 1989, a total of 3, 121 human sera collected from dif ferent population groups in six ecological zones of Nigeria were teste d for the presence of antibodies to Rift Valley fever (RVF) virus by t he haemagglutination-inhibition test. All reactive sera were further t ested by the plaque reduction neutralisation test and specific RVF imm unoglobulin M (IgM) assay. A total of 461 sera (14.8%) demonstrated ha emagglutination-inhibiting antibody and 390 of the 461 initially react ive sera (84.6%) revealed neutralising antibodies. A significantly hig her exposure to the virus was found among livestock workers and wildli fe rangers than in other categories of people tested. The rate of posi tive reactions was higher in adults of 30 years or more than in younge r age groups. Of 461 sera tested for specific RVF IgM, 107 gave positi ve results (23.2%). The highest prevalence of RVF IgM was found among livestock and forestry workers. In the longitudinal survey, an RVF vir us infection rate of 6.7% was demonstrated. The infection rate was sig nificantly higher during the wet season than during the dry season of the same year.