Rift Valley fever (RVF) is a zoonotic viral disease that can affect a variety of species, including ruminants and camels, causing high mortality in young animals and/or abortions in adults. The RVF virus is endemic mainly in subSaharan Africa, but it has also been seen in North Africa, and may have become established in Egypt. There are concerns that this virus might be spreading, after outbreaks were reported in Saudi Arabia and Yemen in 2000. Rift Valley fever tends to occur in periodic epidemics, which typically occur after heavy rainfalls and may be devastating to domesticated livestock. These outbreaks are thought to begin when dormant, infected mosquito eggs hatch in flooded areas. However, the epidemiology of Rift Valley fever is incompletely understood, and low levels of infection have now been identified during interepidemic periods.

Rift Valley fever outbreaks in domesticated animals are often accompanied by human disease. Many human cases are caused by occupational exposure to blood and tissues from infected animals, but mosquito-borne transmission can also occur. The most common form of the disease is a self-limiting, flu-like illness. Complications in a minority of cases include ocular disease, neurological signs, kidney dysfunction and a life-threatening hemorrhagic syndrome with hepatic dysfunction. Although overall case fatality rates are thought to be low (≤ 2%), there may be very large number of cases during some epidemics, resulting in hundreds of serious cases and significant numbers of deaths.