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Rift Valley Fever

Rift Valley Fever is a viral disease of cattle and sheep that was first discovered in the Rift Valley of Kenya. The disease is spread to livestock through the bite of infected mosquitoes during years of heavy rainfall. The disease causes high death rates in young animals and abortions in older animals. Outbreaks of Rift Valley Fever have caused famine in endemic areas.

Rift Valley Fever is zoonotic, meaning that it can spread to people through contact with infected livestock. In addition to airborne spread of the virus, humans can become infected through handling undercooked meat, blood or raw milk. Rift Valley Fever is typically mild in humans but can be severe.

Endemic Areas


Clinical Signs

  • Fever
  • Anorexia (poor appetite)
  • Weakness
  • Death in young animals
  • Abortion (may be 100% in the herd)


There is no specific treatment for Rift Valley Fever. Any animal suspected of having Rift Valley Fever should be reported to the State Veterinarians or USDA Area Veterinarian in Charge immediately.


Human and animal vaccines exist for those areas where Rift Valley Fever is endemic. Control of the mosquito population is also necessary to prevent the spread of the disease.

Public Health

Rift Valley Fever is a highly zoonotic disease, meaning that it can be transmitted from animals to people readily. The disease is typically mild with patients showing flu-like symptoms and photophobia (sensitivity to light). Recovery often occurs in seven days and is uneventful.

In rare cases, people with Rift Valley Fever may develop severe complications including eye disease, meningoencephalitis (inflammation of the brain and surrounding tissue) or hemorrhagic fever. Patients who develop eye disease as a result of Rift Valley Fever often experience permanent vision loss, but the disease is not fatal.

However, those patients who develop hemorrhagic fever often have vomiting and diarrhea with blood and may bleed from the gums. These patients also may develop liver complications. The mortality rate is approximately 50% in patients with hemorrhagic fever.

Rift Valley Fever may be prevented by taking appropriate measures to control mosquitoes and using personal protection equipment (gloves, surgical masks, etc.) when working with potentially infected animals.

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