People with Rift Valley virus infections typically have a flu-like illness with fever, weakness, back pain, dizziness, and weight loss. Infected people usually get better in 2 days to 1 week after the start of the illness. Diagnosis can be made by use of several types of laboratory tests. The drug ribavirin is being studied for its effectiveness against Rift Valley fever. Those who die are usually malnourished, sick with other diseases, or far from good medical care.
Death rates are much higher for infected animals.
The Rift Valley virus was first isolated in 1931 in livestock on a farm in Kenya. The most notable epizootic occurred in Kenya in 1950-1951 and resulted in the death of an estimated 100,000 sheep. In 1978, the virus was detected in Egypt and caused a large outbreak of illness in animals and humans. The first epidemic of Rift Valley fever in West Africa was reported in 1987. It was linked to construction of the Senegal River Project, which caused flooding in the lower Senegal River area.