Rift Valley Fever

Type: Viral

Geography: Sub-Saharan Africa

Cases Per Year: 100 to 1,000 cases

Fatality Rate: less than 1%

First Discovered: 1931 in the Rift Valley of Kenya

The virus primarily affects animals but can also affect humans. The majority of human infections result from contact with the blood or organs of infected animals or the bites of infectious mosquitos. To date, no human-to-human transmission of the Rift Valley Fever virus has been documented.

The incubation period is between 2 and 6 days. Most infections are either asymptomatic or mild. Symptoms include flu-like fever, muscle pain, joint pain, and headache. Some patients develop neck stiffness, sensitivity to light, loss of appetite, and vomiting. These symptoms usually last from 4 to 7 days. In a small percentage of patients, the virus takes a severe form in humans, causing ocular disease, meningoencephalitis, and/or hemorrhagic fever. The severe symptoms occur usually 1 to 4 weeks following the onset of the virus. The case fatality rate for who develop hemorrhagic fever form is about 50%, but the overall case fatality rate is low.

Photo: Rift Valley Fever virions inside of cells – Electron micrograph.