Seroepidemiology of spotted fever group rickettsial infections in humans in Zimbabwe

Abstract

In sera collected throughout Zimbabwe the prevalence of antibodies reactive with Rickettsia conorii (Kenya) and a Zimbabwean spotted fever group rickettsia (ZSFR) was investigated using an indirect immunofluorescence assay (IFA). A random sample of these sera was also tested using a commercial IFA test. There was close agreement between IFA titres using the African rickettsial antigens and the commercial antigen slides. When differences in titre were detected, these were rarely greater than a twofold serum dilution. In Western blot immunoassays, IFA positive human sera detected immunogens of ZSFR and R. conorii (Kenya) that could also be demonstrated with homologous mouse antisera. The overall seroprevalence was 52% to R. conorii (Kenya) and 55% to ZSFR. For both antigens the highest seroprevalence was recorded from the south of the country, where the highest incidence of clinical tick-bite fever was reported in a questionnaire survey to medical practitioners. No difference was found between the seroprevalence in males and females, but high titres of antibody were common in samples from young people.