Rift Valley fever (RVF) is a viral zoonosis that primarily affects animals but also has the capacity to infect humans.
Most human RVF infections with RVFV result in a mild febrile illness. However, with low incidence the disease may also run a fatal course, accompanied by a severe haemorrhagic fever. In animals RVFV causes severe disease in ruminants like cattle, sheep, camels and goats. Sheep appear to be more susceptible than cattle or camels. Age has also been shown to be a significant factor in the animal's susceptibility to the severe form of the disease: over 90% of lambs younger than a week infected with RVF die, whereas mortality among adult sheep can be as low as 10%.
The rate of abortion among pregnant infected ewes is almost 100%. The incubation period is approximately 2 to 6 days and is followed by an abrupt onset of fever, chills and general malaise.
Mosquitoes, mainly theAedes VexansandCulex pipien species,are the only important biological vectors of RVF virus. RVF virus is a member of the Phlebovirus genus, one of the five genera in the familyBunyaviridae.
The virus was first identified in 1930 from an infected newborn lamb as part of an investigation of a large epizootic of disease causing abortion and high mortality in sheep in the Rift Valley of Kenya. Since that time, large outbreaks have been reported in various areas of sub-SaharanAfrica. In 1997-98, and 2006-07 a major outbreak occurred inKenya,SomaliaandTanzaniaand in September 2000, RVF cases were confirmed inSaudi ArabiaandYemen, marking the first reported occurrence of the disease outside the African continent and raising concerns that it could extend to other parts of Asia andEurope. In 2006-2007, major outbreaks occur in East Africa (Tanzania,Kenya) and one year later, inMadagascarandMayotteisland.
Technical disease cards OIE
Information on Rift Valley Fever (DEFRA)
Factsheet: Rift Valley Fever (WHO)
EPIZONE and Rift Valley fever
- A discussion group on bluetongue disease has been established in which experts from both outside and inside EPIZONE were invited to participate. This group has already exchangedinformation by e-mail with Rift Valley fever virus vaccines group.
Surveillance and epidemiology
- In WP6.4 molecular epidemiology is studying genetic relationships between pathogens (including o.a Rift Valley fever and also bacterial and mycoplasmal diseases such as e.g. contagious bovine pleuropneumonia). To support this, two web-based molecular epidemiology servers are being developed.