Prevalence of antibodies against Rift Valley fever virus in Kenyan wildlife

Abstract

Rift Valley fever virus (RVFV) is an arbovirus associated with periodic outbreaks, mostly on the African continent, of febrile disease accompanied by abortion in livestock, and a severe, fatal haemorrhagic syndrome in humans. However, the maintenance of the virus during the inter-epidemic period (IEP) when there is low or no disease activity detected in livestock or humans has not been determined. This study report prevalence of RVFV-neutralizing antibodies in sera (n=896) collected from 16 Kenyan wildlife species including at least 35% that were born during the 1999-2006 IEP. Specimens from seven species had detectable neutralizing antibodies against RVFV, including African buffalo, black rhino, lesser kudu, impala, African elephant, kongoni, and waterbuck. High RVFV antibody prevalence (>15%) was observed in black rhinos and ruminants (kudu, impala, buffalo, and waterbuck) with the highest titres (up to 1:1280) observed mostly in buffalo, including animals born during the IEP. All lions, giraffes, plains zebras, and warthogs tested were either negative or less than two animals in each species had low (<or= 1:16) titres of RVFV antibodies. Of 249 sera collected from five wildlife species during the 2006-2007 outbreak, 16 out of 19 (84%) of the ruminant (gerenuk, waterbuck, and eland) specimens had RVFV-neutralizing titres >or= 1:80. These data provide evidence that wild ruminants are infected by RVFV but further studies are required to determine whether these animals play a role in the virus maintenance between outbreaks and virus amplification prior to a noticeable outbreak.

Fig. 1

Number of animals (%) positive for RVFV-neutralizing antibodies in sera collected from nine species of wild animals in Kenya. Animals testing positive included buffalos (· · ·◆· · ·, n=237), black rhinos (––■––, n=43), and a variety of animals (– –▲– –, kudus, waterbucks, elephants, Thomson's gazelles, and impalas; n=120). The cut-off of 1:10 serum dilution was used to minimize non-specific serum toxicity.

Fig. 2

Map of Kenya showing the seven districts (shaded black) where RVFV-positive buffalos were identified.