Key facts

• Rift Valley Fever (RVF) is a viral disease that primarily affects animals such as sheep, cattle and goats.
• It is transmitted to humans either through contact with the blood or body parts of diseased animals, or mosquito bites
• Most human infections are mild, but severe cases can lead to haemorrhagic fever, encephalitis, or vision loss.
• The disease is endemic in parts of Africa and the Arabian Peninsula.
• It is classed as a priority pathogen by the World Health Organization due to the lack of effective vaccines and treatments and its pandemic potential

Overview

Rift Valley Fever is a zoonotic disease, meaning it can be transmitted from animals to humans. Outbreaks have occurred in parts of Africa and the Middle East.

The virus primarily affects livestock such as camels, sheep and cows. In humans, symptoms range from mild to a severe haemorrhagic form that is fatal in around half of cases.

Outbreaks often occur after heavy rain and flooding, due to a rise in mosquito populations. They can wreak significant economic damage due to people losing livestock.

Signs and symptoms

Most human infections are mild and may be symptomless. When symptoms do appear, they generally develop within two to six days and may include:

• Fever
• Muscle pain
• Joint pain
• Headache
• Fatigue.

Dangers and complications

Severe cases, affecting a smaller proportion of patients, may present with:

• Haemorrhagic fever with bleeding (less than 1 per cent of cases)
• Encephalitis, causing neurological symptoms such as seizures or confusion (less than 1 per cent of cases)
• Eye complications, potentially leading to temporary or permanent vision loss (less than 2 per cent of cases)

Transmission

Rift Valley fever is primarily transmitted to humans through contact with the blood, bodily fluids, or tissues of infected animals. Handling sick animals or slaughtering them increases the risk of infection. There is some evidence that humans can become infected when consuming unpasteurised or uncooked milk of affected animals

The virus can also be transmitted via the bits of infected mosquitoes, particularly Aedes and Culex, and outbreaks often follow periods of heavy rainfall and flooding, which create ideal conditions for mosquito breeding. Human-to-human transmission is extremely rare.

Treatment

There is no specific treatment and management of the disease is primarily supportive and focuses on relieving symptoms. Those with mild disease can take medication such as ibuprofen and should stay hydrated.

Research into antiviral therapies and vaccines for humans is ongoing, but currently prevention and supportive treatment remain the main strategies for managing RVF.

Prevention

Preventing Rift Valley Fever focuses on reducing exposure to infected animals and mosquitoes. This includes:

• Using protective clothing and gloves when handling livestock
• Avoiding consumption of raw milk or undercooked meat from potentially infected animals
• Using mosquito nets, insect repellents, and eliminating breeding sites

Vaccines have been developed for animal use and these are used for outbreak control.

In July 2025 the Coalition for Epidemic Preparedness Innovations launched the first ever phase II trial of a Rift Valley fever vaccine in Kenya.

History

The virus was first identified in Kenya’s Rift Valley in 1931 during an investigation into an outbreak among sheep. Since then outbreaks have been reported in sub-Saharan Africa but in 1977 there was a large number of cases in Egypt when the virus was introduced via the trade of infected livestock. In 1997-8 there was another outbreak in Kenya, Somalia and Tanzania after a period of extensive flooding. In 2000 cases were reported outside Africa for the first time when the virus migrated to Saudi Arabia and Yemen – the trade of infected livestock was blamed for the spread of the disease.

Useful links

who.int/rift-valley-fever

cdc.gov/rift-valley-fever

cepi.net/rift-valley-fever

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