Rift Valley fever

What is Rift Valley fever virus?

Rift valley fever is a disease of ruminants (cattle, sheep, goats) and humans that is currently manifested on the African continent. The disease can affect millions of animals and tens of thousands of people during outbreaks. The disease is caused by the Rift Valley fever virus (family Phenuiviridae, genus Phlebovirus, order Bunyavirales). It can be transmitted by many different mosquito species. Research has shown that the mosquito species most prevalent in the Netherlands, Culex pipiens, can also transmit the virus after feeding on infected sheep.

Where does Rift Valley fever virus occur?

The disease was for the first time described after a large outbreak that occurred on a sheep farm in the Rift Valley in Kenya in 1930. Since that time, large outbreaks have occurred across Africa and the Arabian Peninsula. However, the mosquitoes that spread the virus in these areas are also found in (Western) Europe and (North) America. Hence the growing concern that this virus could establish itself in other areas.

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What are symptoms of Rift Valley fever virus?

Most infections of Rift Valley fever in humans manifest as a transient, flu-like illness. However, a small percentage of humans develop encephalitis or hemorrhagic fever, which may be fatal.

In animals the virus causes severe disease in ruminants like sheep, cattle, goats and camels. Sheep are the most susceptible target species. 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 three weeks of age may succumb to the infection. The rate of abortion among pregnant infected ewes is almost 100 percent. The incubation period is approximately 2 days and is followed by an abrupt onset of fever and general malaise.

Is a vaccine available?

There are currently no vaccines or antiviral drugs against the virus for humans. For use in animals, three different vaccines are available in Africa. None of these vaccines is registered for use in Europe.

Wageningen Bioveterinary Research (WBVR) has developed a new live attenuated vaccine in its BSL3 laboratory together with partners. This vaccine can be used in animals and humans and combines safety and effectiveness. Additional safety and efficacy studies are currently being conducted. The vaccine is also being prepared for a first evaluation in humans. WBVR is partner in this project: Rift Valley fever vaccine development project Larissa.

We expect that the vaccine will become available for both Africa and Europe within a few years and that it will prevent future deaths, animal suffering and economic damage.