Rift Valley fever

Rift Valley fever

Rift Valley fever (RVF) is a viral zoonosis that primarily affects animals but also has the capacity to infect humans. Wageningen Bioveterinary Research conducts research on this disease.

Infection with Rift Valley fever

Most human RVF infections with the virus 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 the virus 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 percent of lambs younger than a week infected with Rift Vally fever die, whereas mortality among adult sheep can be as low as 10 percent.

The rate of abortion among pregnant infected ewes is almost 100 percent. The incubation period is approximately 2 to 6 days and is followed by an abrupt onset of fever, chills and general malaise.

The virus

RVF virus is a member of the Phlebovirus genus, one of the five genera in the family Bunyaviridae. Mosquitoes, mainly the Aedes Vexansand Culex pipien species, are the only important biological vectors of RVF virus.

Outbreaks

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-Saharan Africa. In 1997-98, and 2006-07 a major outbreak occurred in Kenya, Somalia and Tanzania and in September 2000, RVF cases were confirmed in Saudi Arabia and Yemen, marking the first reported occurrence of the disease outside the African continent and raising concerns that it could extend to other parts of Asia and Europe. In 2006-2007, major outbreaks occur in East Africa (Tanzania, Kenya) and one year later, in Madagascar and Mayotte island.