Why early detection of Rift Valley Fever in human beings is difficult

A woman blowing her nose. [Courtesy/GettyImages]

Rift Valley Fever (RVF) is a viral disease that affects both animals and humans, making it a zoonotic illness of concern across Kenya.

According to the World Health Organisation (WHO), the disease is caused by a virus transmitted mainly through mosquitoes. It can also spread to humans through contact with infected animals or their fluids.

Khadija Chepkorir, a veterinary epidemiologist at the Zoonotic Disease Unit, explains that the disease becomes common after heavy rains and flooding.

“This creates ideal breeding grounds for the Aedes aegypti mosquito, the main vector of the virus,” said Dr Khadija

The disease was first identified in 1931 near Naivasha during a sheep epidemic and has since spread to other counties, including Murang’a, showing it is no longer limited to the Rift Valley

In animals, RVF mostly affects cattle, sheep, goats and camels. “The main signs are abortion storms in pregnant animals, death in young animals, and bleeding from the nose, mucous membranes, or through bloody diarrhoea,” Khadija says

Sheep are the most vulnerable, followed by cattle, goats and camels.

These infections in livestock are central to human outbreaks because people are exposed when they handle blood, body fluids or aborted material without protective gear.

She warns that slaughtering, butchering or handling carcasses is risky if done without gloves or protective clothing.

“Although mosquito bites can infect humans, close contact with sick animals or their remains is the most common way the virus spreads,” she explains.

Humans usually develop flu-like symptoms, which makes early detection difficult.

Okunga Emmanuel, Senior Deputy Director of Medical Services and head of the Zoonotic Disease Unit, says that symptoms such as fever, chills, body aches and fatigue can easily be confused with malaria, typhoid or dengue.

“Severe cases may involve haemorrhagic symptoms, meningitis or eye disease that can cause permanent vision loss. The fatality rate in severe haemorrhagic cases can reach 50 per cent,” Dr Okunga adds.

Diagnosis depends on recognising these symptoms, assessing a patient’s occupation or residence, and confirming the infection through laboratory tests. Health workers must follow strict biosafety procedures when handling samples to avoid accidental infection.

Okunga notes, “Early detection is often challenging in rural areas because of limited mosquito surveillance and shortages of trained personnel and testing capacity.” To stay ahead of outbreaks, Kenya uses an early warning system that connects weather predictions, rainfall patterns and mosquito surveillance data.

The WHO states that strong monitoring and timely laboratory confirmation are crucial for managing RVF.

There is no specific antiviral treatment for the disease in humans, so care is mainly supportive. Prevention is therefore essential. Okunga advises communities to avoid handling sick animals without protective gear and to use mosquito nets, repellents and environmental sanitation. Vaccinating livestock in high-risk areas is an important part of reducing virus circulation.

“When we prevent animals from getting sick, we prevent transmission to humans,” he says. “This also protects farmers’ livelihoods and the national economy because outbreaks can disrupt meat exports and local markets.”

Khadija encourages farmers to vaccinate animals before the rainy season or during alert periods.

“Vaccines are available at the Kenya Veterinary Vaccines Production Institute and should be used before mosquitoes become widespread,” she advises

The virus spreads more widely during heavy rains because infected mosquito eggs hatch after flooding, leading to an increase in mosquito populations.

Humans are most at risk when they handle infected animals, although mosquito transmission also occurs. Khadija urges farmers to use gloves when dealing with sick animals and to call veterinarians whenever possible.

RVF is no longer confined to the Rift Valley. “The risk is rising in other parts of the country, with cases now reported in counties such as Murang’a and Siaya, so everybody is potentially at risk,” Okunga warns.

Environmental factors such as deforestation and excavations that create water pools also contribute to mosquito breeding and spread of the disease.