Rift Valley fever (RVF) is an acute, fever-causing viral disease most commonly observed in domesticated animals (such as cattle, buffalo, sheep, goats, and camels), with the ability to infect and cause illness in humans. The disease is caused by RVF virus (RVFV), a member of the genus Phlebovirus in the family Bunyaviridae. It was first reported in livestock by veterinary officers in Kenya’s Rift Valley in the early 1910s.
RVF is generally found in regions of eastern and southern Africa where sheep and cattle are raised, but the virus exists in most of sub-Saharan Africa, including west Africa and Madagascar. In September 2000, a RVF outbreak was reported in Saudi Arabia and subsequently, Yemen. This outbreak represents the first cases of Rift Valley fever identified outside Africa.
Outbreaks of RVF can have major societal impacts, including significant economic losses and trade reductions. The virus most commonly affects livestock, causing disease and abortion in domesticated animals, an important income source for many. Outbreaks of disease in animal populations are called “epizootics.” The most notable RVF epizootic occurred in Kenya in 1950-1951, resulting in the death of an estimated 100,000 sheep.
Additionally, epizootic outbreaks of RVF increase the likelihood of contact between diseased animals and humans, which can lead to epidemics of RVF in humans. One example occurred in 1977 when the virus was detected in Egypt (possibly imported from infected domestic animals from Sudan) and caused a large outbreak of RVF among both animals and humans resulting in over 600 human deaths. Another example of RVF spillover into human populations occurred in west Africa in 1987, and was linked to construction of the Senegal River Project. The project caused flooding in the lower Senegal River area, altering ecological conditions and interactions between animals and humans. As a result, a large RVF outbreak occurred in animals and humans.