Rift Valley fever spreads mainly from infected animals to people, with mosquitoes also playing a role. Here is how it presents, where outbreaks occur, and how to reduce risk.
What Rift Valley fever is
Rift Valley fever is a viral zoonosis. The World Health Organization describes it as a disease that mainly affects animals but can also infect people. Cattle, sheep, camels and goats are susceptible, and sheep and goats are the most vulnerable. The virus was first identified in 1931 in Kenya's Rift Valley, and it has since been found across much of sub-Saharan Africa, plus Saudi Arabia and Yemen. European health agencies note that no locally acquired human case has ever been recorded inside the European Union or the European Economic Area, although imported cases have appeared in France and the United Kingdom. Because the illness is shared between animals and people, its control depends on livestock surveillance and vaccination as much as on human medicine.
How the virus reaches people
Transmission to people has two main routes. The first is contact with the blood, organs or tissues of infected animals during slaughter, birth assistance, butchering or carcass disposal. The second is the bite of infected mosquitoes, chiefly Aedes and Culex species. The World Health Organization states plainly that most human infections come from that direct or indirect animal contact, not from a bite. Crucially, no human to human transmission has been documented, so a patient is not a risk to a household. The virus also persists between outbreaks in a remarkable way: Aedes mosquitoes can pass it to their eggs, so new generations can carry infection when rains return. That biology helps explain why outbreaks recur in the same places.
Symptoms and severe forms of illness
Most human cases are mild and clear up within four to seven days. Fever, muscle pain and headache are the usual complaints. A small minority of patients develop severe disease, and the numbers matter for honest risk communication. The World Health Organization reports an ocular form in 0.5 to 2 percent of patients, meningoencephalitis in less than 1 percent, and a haemorrhagic form in less than 1 percent. The haemorrhagic form is the most dangerous: the case fatality ratio is about 50 percent for patients who develop it. Those proportions are low, but they explain why clinicians in affected areas treat fever with bleeding or neurological signs as an emergency. Early supportive care, and rapid laboratory confirmation, remain the mainstay of treatment because no licensed human vaccine is available.
Where outbreaks happen
Rift Valley fever is endemic in several African countries, and outbreaks cluster around water and livestock movement. The World Health Organization reported that from 20 September to 30 October 2025, Mauritania and Senegal recorded 404 confirmed human cases and 42 deaths combined. Senegal's 358 cases and 28 deaths were concentrated in the north, with 78 percent in the Saint-Louis region. Mauritania's 46 cases and 14 deaths occurred across eleven districts in thirteen regions, three of which share borders. Both countries also reported animal outbreaks, including abortions and positive samples in goats and dromedaries. The World Health Organization called the event unusual in scale and severity, and rated the national risk high, the regional risk moderate and the global risk low.
What East African data show
A study published in Frontiers in Public Health in December 2024 analysed 67 outbreak reports from six East African Community countries between 2010 and 2024. Rwanda, Uganda, Burundi and Kenya accounted for most events; Tanzania and South Sudan recorded few. Forty four events affected animals only, seventeen people only, and four both. Reports peaked in May and June, then fell to zero to two per month from October to December. The peak year was 2018 with 30 events, which the authors link to rainfall that flooded mosquito habitats after a prolonged drought. Hotspots included Ngozi district in Burundi and Ngoma district in Rwanda. Animal movement control appeared in 17 events and vaccination campaigns in 14.
Mosquito and animal transmission cycles
Mosquitoes do more than bite people. Aedes species spread the virus among animals, and their eggs can carry infection through dry periods, so a herd can be exposed soon after water returns. Culex species also transmit the virus among animals and to people. The European Centre for Disease Prevention and Control notes that Culex pipiens, a mosquito widespread across Europe, has shown high vector competence for the virus in laboratory studies, meaning it can pick up and pass on the infection efficiently. That finding does not mean European outbreaks are likely. It does mean that competent mosquitoes exist far beyond the current outbreak zones, so veterinary and public health surveillance deserve continued investment. Control efforts recorded in the East African review included animal movement restrictions and vaccination campaigns, showing that coordinated veterinary measures remain central to outbreak response.
Protecting people and animals
Practical protection starts with animals. The World Health Organization advises routine livestock vaccination before outbreaks, and notes that sustained animal vaccination programmes can prevent them. People handling sick animals, assisting births or slaughtering should wear protective equipment and avoid fresh blood, raw milk and raw animal tissue. Mosquito bite prevention is also sensible, using intact screens, long clothing and approved repellents correctly. In the 2025 Mauritania and Senegal event, the World Health Organization recommended no travel or trade restrictions, which is standard when the risk is locally contained. No commercial human vaccine exists. An inactivated human vaccine does exist but is not licensed or commercially available. Vaccinating ruminants therefore remains the favoured way to protect people in endemic areas.
Sources
- Rift Valley fever: World Health Organization
- Rift Valley fever- Mauritania and Senegal: World Health Organization
- Rift Valley fever, Annual Epidemiological Report for 2021: European Centre for Disease Prevention and Control
- Rift Valley Fever outbreaks in the East African Community: insights from ProMed data (2010-2024): Frontiers in Public Health via PubMed Central
This article is general information, not medical advice. Ask a doctor or pharmacist about your own health.