In this cross-sectional seroepidemiological study we sought to examine the evidence for circulation of Rift Valley
fever virus (RVFV) among herders in Madagascar and Kenya. From July 2010 to June 2012, we enrolled 459
herders and 98 controls (without ruminant exposures) and studied their sera (immunoglobulin G [IgG] and IgM
through enzyme-linked immunosorbent assay [ELISA] and plaque reduction neutralization test [PRNT] assays) for
evidence of previous RVFV infection. Overall, 59 (12.9%) of 459 herders and seven (7.1%) of the 98 controls were
positive by the IgG ELISA assay. Of the 59 ELISA-positive herders, 23 (38.9%) were confirmed by the PRNT assay
(21 from eastern Kenya). Two of the 21 PRNT-positive study subjects also had elevated IgM antibodies against
RVFV suggesting recent infection. Multivariate modeling in this study revealed that being seminomadic (odds ratio
[OR] = 6.4, 95% confidence interval [CI] = 2.1–15.4) was most strongly associated with antibodies against RVFV.
Although we cannot know when these infections occurred, it seems likely that some interepidemic RVFV infections
are occurring among herders. As there are disincentives regarding reporting RVFV outbreaks in livestock or
wildlife, it may be prudent to conduct periodic, limited, active seroepidemiological surveillance for RVFV infections
in herders, especially in eastern Kenya.
Gray, G.C., Anderson, B.D., LaBeaud, D., Heraud, J.-M., Fèvre, E.M, Andriamandimby, S.F., Cook, E.A.J., Dahir, S., Glanville, W.A. de, Heil, G.L., Khan, S.U., Muiruri, S., Olive, M.-M., Thomas, L.F., Merrill, H.R., Merrill, M.L.M. and Richt, J.A. 2015. Seroepidemiological study of interepidemic Rift Valley fever virus infection among persons with intense ruminant exposure in Madagascar and Kenya. American Journal of Tropical Medicine and Hygiene 93(6): 1364-1370.