Seroepidemiological Study of Interepidemic Rift Valley Fever Virus Infection Among Persons with Intense Ruminant Exposure in Madagascar and Kenya.

Gregory C Gray,Benjamin D Anderson,Elizabeth A J Cook,Eric M Fèvre,Juergen A Richt,Mary L M Merrill,Jean-Michel Heraud,Salah U Khan,Samuel Muiruri,Marie-Marie Olive,Gary L Heil,Soa Fy Andriamandimby,Lian F Thomas,Hunter R Merrill,William A De Glanville,A Desirée Labeaud,Saidi Dahir

doi:10.4269/ajtmh.15-0383

Abstract

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 7 (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.

Highlights

Since its first discovery in 1931,1,2 Rift Valley fever virus (RVFV) has been detected in various sub-Saharan countries, as well as Egypt, Saudi Arabia, and Yemen, causing numerous outbreaks among both animals and humans.[3,4,5,6] Kenya’s most recent Rift Valley Fever (RVF) outbreak of 2006–2007 spread to multiple provinces and districts and resulted in nearly 400 cases of severe illness with at least 118 human deaths.[5,7] Epidemiological data collected from some of the patients demonstrated that two-thirds were exposed to a recently ill animal before infection.[8]
Data suggested that other risk factors, including drinking raw milk, owning an ill animal, working as a herdsman, and slaughtering an animal, were associated with RVFV infection.[5,8]
From January to May 2008 and from November 2008 to March 2009, a RVFV strain, similar to that identified in the 2006–2007 outbreaks in Kenya, was identified as the causative agent in human and animal outbreaks across Madagascar, which resulted in a total of 26 human deaths.[9]

Summary

Introduction

Since its first discovery in 1931,1,2 Rift Valley fever virus (RVFV) has been detected in various sub-Saharan countries, as well as Egypt, Saudi Arabia, and Yemen, causing numerous outbreaks among both animals and humans.[3,4,5,6] Kenya’s most recent Rift Valley Fever (RVF) outbreak of 2006–2007 spread to multiple provinces and districts and resulted in nearly 400 cases of severe illness with at least 118 human deaths.[5,7] Epidemiological data collected from some of the patients demonstrated that two-thirds were exposed to a recently ill animal before infection.[8]. This was not the first epizootic to occur in Madagascar, as outbreaks were reported in the east coast in 1990 and 1991, which resulted in increased abortion rates among pregnant cattle by 17% and 15%, respectively.[10,11]

Methods

Results

Conclusion