An outbreak of Rift Valley Fever has caused the deaths of 42 people between 20 September and 30 October 2025, according to a press release issued by the World Health Organization on 5 November 2025. A total of 404 people have been infected in the two countries, where the disease is considered endemic, as well as a large number of domestic Animals, many of whom have also died. The risk of further spread is considered to be high, due to an exceptional rainy season, which has led to an unusually high level of Mosquito activity (Mosquitos are the main vector for the disease), as well as the widespread movement of Cattle across borders into neighbouring countries, particularly Mali and The Gambia.
In Mauritania, 46 Human cases of Rift Valley Fever were reported between 27 September and 30 October, with 14 deaths (a case fatality ratio of 30%). Infections have been reported in thirteen wilayas (regions), three of which border onto other countries, Assaba, which has a southern border with Mali, and Brakna and Trarza, both of which border Senegal across the Senegal River.
According to the Mauritanian Ministry of Animal Resources, cases in Animals first began to appear in August this year, with the initial cases being in Goats and Dromedary Camels, and cases later appearing in Sheep and Cattle. To date 235 Animals have been confirmed to be infected with the disease, 71 of which have died. The majority of the Animal deaths occurred in Brakna Wilaya, with fatalities also reported in Hodh El Gharbi and Hodh Ech Chargui wilayas, which also border onto Mali.
The last major outbreak of Rift Valley Fever in Mauritania was in 2022, when 47 people are known to have been infected, with 23 fatalities (a case fatality ratio of 49%). Most of those infected were pastoralists, with cases reported in nine of Mauritania's fifteen wilayas.
In Senegal, 358 Human cases of Rift Valley Fever were reported between 20 September and 30 October, with 28 deaths (a case fatality ratio of 7.8%). Cases have been reported in eight of the county's fourteen administrative regions, although 78% of all cases have been in Saint-Louis, the most northerly region, with a long border with Mauritania. Rift Valley Fever has also been reported in Dakar (9 cases), Fatick (12 cases), Kaolack (13 cases), Louga (18 cases), Matam (23 cases), Thiès (2 cases) and Tambacounda (2 cases).
A total of 160 Animals have tested positive for Rift Valley Fever, in nine of the regions of Senegal, with Sheep, Goats and Cattle being affected; seven regions (Dakar, Fatick, Louga, Matam, Saint-Louis, Tambacounda and Thiès) have reported Animal fatalities. However, over the same period, 640 cases of spontaneous abortion in domestic Animals (a common symptom of Rift Valley Fever), which may indicate a larger, undiagnosed, Animal outbreak.
The last recorded outbreak of Rift Valley Fever in Senegal occurred in the Diourbel Region in January 2025, while the last recorded Human infection was in the Saint-Louis Region in 2022.
Rift Valley Fever is a Viral zoonotic disease that primarily affects Animals but also has the capacity to infect Humans. Infection can cause severe disease in both Animals and Humans. The disease also results in significant economic losses due to death and abortion among Rift Valley Fever-infected livestock.
The Rift Valley Fever Virus is a member of the Phlebovirus genus in the order Bunyavirales, of segmented negative-strand RNA Viruses, the group which also includes Hantavirus (Leprosy) and Lassa Virus (Lassa Fever).
The Rift Valley Fever Virus was first identified in 1931 during an investigation into an epidemic among sheep on a farm in the Rift Valley of Kenya. Since then, outbreaks have been reported in sub-Saharan Africa. In 1977 an explosive outbreak was reported in Egypt, the Rift Valley Fever virus was introduced to Egypt via infected livestock trade along the Nile irrigation system. In 1997–98, a major outbreak occurred in Kenya, Somalia and Tanzania following El Niño event and extensive flooding. Following infected livestock trade from the horn of Africa, Rift Valley Fever spread in September 2000 to Saudi Arabia and Yemen, marking the first reported occurrence of the disease outside the African continent and raising concerns that it could extend to other parts of Asia and Europe.
The majority of Human infections result from direct or indirect contact with the blood or organs of infected animals. The Virus can be transmitted to humans through the handling of animal tissue during slaughtering or butchering, assisting with animal births, conducting veterinary procedures, or from the disposal of carcasses or fetuses. Certain occupational groups such as herders, farmers, slaughterhouse workers, and veterinarians are therefore at higher risk of infection.
The Virus infects Humans through inoculation, for example via a wound from an infected knife or through contact with broken skin, or through inhalation of aerosols produced during the slaughter of infected Animals.
There is some evidence that humans may become infected with Rift Valley Fever by ingesting the unpasteurised or uncooked milk of infected Animals. Human infections have also resulted from the bites of infected Mosquitoes, most commonly the Aedes and Culex Mosquitoes and the transmission of Rift Valley Fever Virus by hematophagous (blood-feeding) Flies is also possible. To date, no human-to-human transmission of Rift Valley Fever has been documented, and no transmission of Rift Valley Fever to health care workers has been reported when standard infection control precautions have been put in place. There has been no evidence of outbreaks of Rift Valley Fever in urban areas.
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