What Is Rift Valley Fever?

Medically Reviewed by Melinda Ratini, MS, DO on January 31, 2023
4 min read

Rift Valley fever (RVF) is a disease animals get when they're bitten by a mosquito carrying the Rift Valley fever virus (RVFV). You can get the virus if a mosquito bites you, or from contact with the blood or tissue of an infected animal. But there have been no reported cases of people catching it from other people.

Most people who have the virus don't have any symptoms. It's rarely serious in humans, but it can be fatal in rare cases. (It's often more severe in animals.)

The virus got its name from Kenya's Rift Valley region, where it was discovered in 1931. Since then, there have been numerous outbreaks. Experts believe climate change could make outbreaks more common because it can make it easier for mosquitoes to thrive.

RVF is most common in animals from sub-Saharan Africa -- like camels, cattle, sheep, goats, and buffalo. Though the virus is mostly limited to the Middle East and Africa, regions in North America and Europe have the mosquitoes capable of carrying it and spreading it.

Animals get RVF from infected mosquitoes, but some research says ticks and biting midges may carry it as well.

People can get it if they're bit by an infected mosquito. Humans can also get the virus if they have contact with an infected animal's blood, body fluids, or tissues. This can happen when animals are being killed, or if a person is assisting in an animal giving birth. It can be spread by an infected animal to a person who is treating the animal and comes into contact with infected fluid or tissue. Humans can get it from eating raw or undercooked animal products. People can inhale it as well.

As long as infection control practices are in place, though, people don't seem to be able to spread it to each other. And if practices are followed when people come into contact with infected animals, it can reduce the chance of transmission.

Animals can get severely ill from RVF, but most people have mild illness or no symptoms. In fact, about half of infected people show no signs of the virus whatsoever. If you have symptoms, you may feel like you have the flu. Most people recover within 2 days to 1 week after symptoms start.

Symptoms of RVF in humans include:

  • Fever
  • Dizziness
  • Weakness
  • Back pain

About 8% to 10% of people will have a more severe form of the virus. Those symptoms include:

  • Excessive bleeding (hemorrhage)
  • Brain swelling (encephalitis)
  • Eye disease

A small percentage of people who have severe symptoms experience the following complications:

  • Lesions on the eyes
  • Blurred or decreased vision
  • Permanent vision loss
  • Headache
  • Coma
  • Seizures
  • Jaundice
  • Liver problems
  • Vomiting blood
  • Bloody stool
  • Death

Your doctor can tell if you have RVF by collecting a sample of your blood. That's the only way to tell for certain if you have it.

There's no specific medicine to treat Rift Valley fever. You can take over-the-counter medications to manage symptoms like fever.

People with more severe cases are usually hospitalized and get supportive care for symptoms and complications.

Most people recover within 2 days to 1 week after they feel ill. Only about 1% of people with RVF die from the disease.

These are a few ways to prevent yourself from getting RVF.

  • Pay attention to travel advisories if you're traveling globally. They can help you tell if you're going to an area with an outbreak.
  • If you're in one of those areas, it may be best to sleep indoors.
  • Take precautions to avoid mosquito bites, such as using mosquito repellent and wearing long-sleeved shirts and pants. Outbreaks often happen in areas that get ongoing rain, which can raise mosquito activity.
  • Use protective gear if you expect to come into close contact with animals in an affected region.

There is an experimental vaccine for humans, but it has only been tested on professionals, such as people who treat animals or work in slaughter facilities. There's no commercially available form of a vaccine for the general public. Vaccines for animals exist, which may reduce the spread of the virus. Efforts to vaccinate animals have been difficult not only because the safer vaccines require multiple dosing, but the live virus vaccines can cause birth defects and lead to fetal death in livestock. Another problem is that areas often lack electricity to safely store the vaccines.

Some experts say global warming plays a role in the potential more widespread risk of Rift Valley fever. As temperatures rise, it could expand where mosquitoes can spread the virus. Mosquitoes are vectors (meaning they carry the virus) and can transmit the virus more often after heavy rainfall. Climate change can shift the ecology of mosquitoes, so it can impact human (and animal) health.

The World Health Organization (WHO) has listed Rift Valley fever as a priority on its WHO R&D Blueprint for epidemics. This helps them prioritize tests and treatments, including vaccines. Researchers are looking at multiple vaccine agents in hopes to develop one that's safe and effective.