• Rift Valley fever is a fever-causing viral disease that affects livestock and humans in Africa. It is most common during years of heavy rainfall.
• People get Rift Valley fever mainly from the bite of an infected mosquito. The disease can also be spread by contact with the blood or body fluids of an infected animal.
• Rift Valley fever can cause serious eye infection, inflammation of the brain, severe bleeding (hemorrhage), and death.
• To prevent Rift Valley fever, travelers to Africa should take precautions against insect bites: 1) use insect repellent, 2) wear long sleeves and pants, and 3) use bednets. Travelers should also avoid contact with livestock in areas where outbreaks of Rift Valley fever are occurring.

What is Rift Valley fever?

Rift valley fever is a fever-causing disease that affects livestock (including cattle, buffalo, sheep, and goats) and humans in Africa. It is named after a trough stretching 4,000 miles from Jordan through eastern Africa to Mozambique. Rift Valley fever is spread mainly by infected mosquitoes and appears most often during years of heavy rainfall.

Where is Rift Valley fever found?

Rift Valley fever is most common in the livestock-raising regions of eastern and southern Africa. The disease is also found in most countries of sub-Saharan Africa and in Madagascar.

What is the infectious agent that causes Rift Valley fever?

The disease is caused by the Rift Valley fever virus.

How do people get Rift Valley fever?

• People can get Rift Valley fever from the bite of mosquitoes and possibly other blood- sucking insects. The virus usually lies dormant in the eggs of Aedes mosquitoes. During heavy rains and floods, the eggs hatch large numbers of infected mosquitoes that feed on livestock and spread the virus. Other species of mosquitoes, and possibly other biting insects, can also become infected and spread the disease. The occurrence of disease in a large number of domestic animals is referred to as an "epizootic." The presence of a mosquito-borne epizootic can lead to an epidemic in humans.
• People can get Rift Valley fever if they are exposed to the blood or other body fluids of infected animals. This can happen during the slaughtering or handling of infected animals or during the preparation of food.
• Laboratory workers have become infected through airborne transmission during work with virus cultures or laboratory samples containing the virus.

What are the signs and symptoms of Rift Valley fever?

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. Sometimes, however, the infection can cause hemorrhage (severe bleeding), encephalitis (inflammation of the brain), or severe eye complications.

How is Rift Valley fever diagnosed?

Diagnosis can be made by use of several types of laboratory tests.

Who is at risk for Rift Valley fever?

• People who sleep outdoors at night in areas where outbreaks occur
• Animal herdsmen, slaughterhouse workers, veterinarians, and others who handle tissues of infected animals in areas where the virus is present
• International travelers who visit areas where the virus is present during periods when outbreaks or epidemics are occurring

What is the treatment for Rift Valley fever?

The drug ribavirin is being studied for its effectiveness against Rift Valley fever.

What complications can result from Rift Valley fever?

The most common complication is inflammation of the retina (a structure connecting the nerves of the eye to the brain). About 1% to 10% of affected persons might have some resulting vision problems or partial blindness.

Approximately 1% of infected people die of the disease. Those who die are usually malnourished, sick with other diseases, or far from good medical care. Death rates are much higher for infected animals.

Is Rift Valley fever an emerging infectious disease?

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. In late 1997, after exceptionally heavy rains, an epidemic resulted in the deaths of at least 300 people and large numbers of animals in remote parts of northeastern Kenya, southern Kenya, and southern Somalia.

How can Rift Valley fever be prevented?

No licensed vaccine or virus-killing medicine is available for human use. Travelers to Africa should always wear long sleeves and pants and use insect repellents and bednets to protect against bites from mosquitoes and other blood-sucking insects. Persons who work with animals in areas where the virus is present should avoid exposure to the blood or tissues of potentially infected animals.
This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health-care provider. If you have any questions about the disease described above, consult a health-care provider.