In early November 2025, the World Health Organization (WHO) confirmed an outbreak of Rift Valley Fever (RVF) affecting Mauritania and Senegal in Western Africa. Between late September and October 2025, national authorities reported more than 404 confirmed human cases and over 42 deaths. With a case fatality rate approaching 10%, this outbreak has again drawn attention to one of the most persistent viral zoonoses of Africa.
RVF is recognised by the World Health Organisation for Animal Health as a notifiable animal disease, reflecting its potential for rapid cross-border spread among livestock. The WHO’s R&D Blueprint for Action to Prevent Epidemics also lists it as a priority pathogen with epidemic potential, underscoring the need for urgent research and preparedness. Because of its capacity to cause widespread illness in animals and humans, the virus is also considered to have possible use as a biological weapon, highlighting the importance of global surveillance and coordinated response mechanisms.
Origin and history
RVF derives its name from Kenya’s Rift Valley, where the disease was first recognised in the early 1930s during an investigation into mysterious livestock deaths. Since then, the infection has appeared across sub-Saharan Africa, often after unusually heavy rains. In 1977, it spread northwards to Egypt, and by 2000, it had crossed the Red Sea into Saudi Arabia and Yemen, marking its first confirmed appearance outside the African continent.
Epidemiological triad
The disease is caused by a Phlebovirus belonging to the Phenuiviridae family. It primarily affects animals such as sheep, goats, cattle, and camels. Humans become infected through close contact with infected animals or by the bite of infected mosquitoes. The virus has not been shown to spread from person to person. The incubation period typically ranges from 2 to 6 days after exposure to the virus. Multiple mosquito species can transmit the Rift Valley fever virus, and the predominant vector differs from one region to another. In various ecological settings, different mosquito species contribute uniquely to the maintenance and spread of the infection.
Among animals, sheep and goats are most vulnerable. Humans at greatest risk are herders, farmers, veterinarians, and slaughterhouse workers. Exposure often happens while handling blood, organs, or raw milk from infected animals. Environmental conditions, such as heavy rainfall and flooding, create breeding grounds for mosquitoes and often signal the onset of new outbreaks. Human infection typically occurs through two routes: mosquito bites or direct contact with infected animal fluids. Since there is no evidence of human-to-human transmission, standard infection control precautions are sufficient in healthcare settings.
Clinical manifestations
In about 90 % of cases, RVF presents as a mild, flu-like illness that begins two to six days after infection. The onset is marked by high fever, muscle and joint pain, headache, weakness, and backache, sometimes accompanied by nausea, vomiting, and sensitivity to light. These symptoms usually last for three to seven days, and most people recover completely without any lasting effects.
In a small proportion of patients, however, the disease progresses to a severe form affecting the eyes, brain, or liver. Ocular disease occurs in approximately 0.5% to 2% of cases. It leads to blurred vision, floating spots, and eye pain due to inflammation of the retina. If the macula is involved, permanent vision loss may result. Meningoencephalitis develops in less than 1%, presenting with confusion, dizziness, seizures, or coma, and may cause long-term neurological complications. The haemorrhagic form, also seen in less than 1%, is the most fatal, characterised by jaundice, bleeding from the nose, gums, or stomach, and liver failure, leading to death in nearly half of these patients within a week of onset. The most severe form is the haemorrhagic variety, which can lead to liver failure and internal bleeding and has a fatality rate approaching 50%.
Diagnosis and treatment
Diagnosing RVF is challenging in endemic areas because it mimics malaria, typhoid, and other febrile illnesses. Confirmation requires laboratory testing using molecular or serological methods under high biosafety precautions. Currently, there is no specific antiviral treatment. Medical care is primarily supportive, focusing on maintaining hydration, monitoring for organ failure, and preventing complications related to bleeding. No licensed human vaccine is commercially available, though experimental inactivated vaccines have been used for high-risk occupational groups. In animals, vaccines exist; however, they are most effective when used between outbreaks, as large-scale vaccination during an outbreak can inadvertently spread the infection.
One Health response
Outbreak management follows a One Health framework that links human, animal, and environmental health. Animal surveillance aims to detect unusual livestock abortions early, while movement restrictions limit the spread. Vector control focuses on draining stagnant water and reducing the breeding of mosquitoes. Public health education advises farmers and abattoir workers to use gloves and masks while handling animals and to avoid consuming raw milk. Healthcare facilities are advised to follow strict sample-handling procedures, and community communication campaigns emphasise the importance of early reporting of sick livestock. For pastoral communities, Rift Valley fever is a medical threat and an economic disaster. Massive livestock abortions and deaths reduce family incomes and threaten regional food security.
Indian perspective
India has not reported any outbreak of Rift Valley fever. Nevertheless, climatic conditions that favour mosquito breeding, coupled with large livestock populations and international trade, mean that preparedness remains vital. The disease is classified as an exotic zoonosis of concern under India’s One Health surveillance framework. Strengthening diagnostic laboratories, veterinary surveillance, and border inspections is part of national preparedness planning. So far, no cases have been detected in humans or animals within India.
The WHO has not recommended any travel or trade restrictions to the affected regions of Mauritania and Senegal, where the current RVF outbreak has been reported.Although the disease remains geographically limited, its ability to emerge following heavy rains and floods makes it a recurring concern across Africa and the Arabian Peninsula.
(Dr. C. Aravinda is an academic and public health physician. The views expressed are personal. aravindaaiimsjr10@hotmail.com)
Published – November 10, 2025 12:40 pm IST
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