The disease is caused by the Rift Valley fever virus, an RNA virus in the genus Phlebovirus in the family Bunyaviridae.
The RVF virus is endemic in Africa and Middle East.
Outbreaks of RVF often cause substantial socio-economic and public health impacts. High abortion and mortality rates in animals result in reduction in livelihoods and food security. The total yearly cost of the disease is estimated to be US $427 million.
RVF strikes in periodic epidemics, which typically occur after heavy rainfalls. Rift Valley fever is transmitted by mosquitoes, which act as biological vectors. RVF virus can be transmitted in the womb to the fetus. Humans can acquire RVF virus by direct contact with infected tissues, by aerosol containing viruses generated in laboratories and during slaughter, or from mosquitoes.
The incubation period is thought to be one to three days. In endemic regions, epidemics of RVF are characterized by high mortality in newborn animals and abortions in adults. Between epidemics, this virus can circulate without apparent clinical signs. Nonspecific signs of fever, anorexia, weakness, lymphadenopathy, respiratory signs and hemorrhagic diarrhoea can be seen in young animals.
Vaccines are used to protect animals in endemic regions, but they may cause abortions in pregnant animals. Vaccination of animals may also protect people by reducing amplification of the virus. Breeding sites of mosquitoes are usually extensive, making disease prevention by vector control impractical.
For further information, view our RVF product development work.