Prevalence of Rift Valley Fever Immunoglobulin G Antibody in Various Occupational Groups Before the 2007 Outbreak in Tanzania

A cross-sectional sero survey of 199 apparently healthy persons from various occupations was carried out in Tanga, Tanzania in November 2004 to investigate exposure to Rift Valley fever (RVF) virus. Sera were tested for the presence of antibodies to RVF virus by the inhibition enzyme-linked immunosorbent assay (ELISA) for detecting immunoglobulin G (IgG). All reactive sera were further tested by the capture ELISA test and specific RVF immunoglobulin M (IgM) assay. Eight (4.0%) tested positive for IgG and none of the samples tested positive for IgM. Among the occupational groups examined, the seroprevalence was 7.3%, 1.5%, and 9.5% in the abattoir workers, livestock keepers, and others categories, respectively. Seropositivity was higher in men (5.3%) than women (1.5 %) and increased markedly in men aged between 20 to 40 years, with no significant differences among the age groups and sexes. The results indicate that a small proportion of people in Tanga municipality were exposed to RVF virus infection prior to 2007 disease outbreak in Tanzania. These findings need to be taken into consideration when future disease control programs are implemented.