• Above-average rainfall driven by El Niño is increasing the risk of Rift Valley Fever outbreaks across the Horn of Africa, posing serious threats to both human health and livestock-dependent livelihoods.
• Rift Valley Fever spreads rapidly following heavy rains due to surging mosquito populations, with high mortality rates among young livestock and significant risks for people who handle infected animals.
• Early prevention measures, including timely livestock vaccination and strong disease surveillance, are critical, as the window to effectively control outbreaks closes quickly once cases begin to appear.

Livestock and human deaths likely if disease surveillance, prevention, and control measures fall short

Above-average rains associated with El Niño are putting some countries at higher risk of mosquito-borne diseases that threaten both lives and livelihoods, according to the Famine Early Warning Systems Network (FEWS NET).

In an October alert, FEWS NET projected that certain regions, including Afghanistan and the Horn of Africa, would experience stronger-than-normal seasonal rainfall as a result of the ongoing El Niño event.

While heavy rains are expected to aid drought recovery in the eastern Horn of Africa, FEWS NET also warned of concerns including flooding, short-term population displacement, and in some cases, disease spread.

Rift Valley Fever (RVF) is one mosquito-borne disease likely to affect the Horn of Africa as the region continues to receive above-average rains through the end of 2023.

“RVF is a viral zoonotic disease that can affect livestock and humans,” USAID Livestock Advisor Dr. Shaina Craige said. “Rises in large outbreaks of RVF most commonly occur after periods of heavy rainfall, which leads to an abundance of mosquitoes.”

People are mainly exposed to RVF through contact with infected animals. Transmission usually occurs among those who work closely with livestock, including herders, farmers, slaughterhouse workers, veterinarians, and community animal health workers.

Most people infected with RVF either show no symptoms or suffer from a mild illness that includes fever, weakness, back pain, and dizziness. However, in severe cases, eye disease, brain tissue inflammation, hemorrhagic fever, or even death may occur. 

While RVF threatens human health, cattle, sheep, goats, and camels are most susceptible to the disease, which is known to kill young livestock and cause sudden abortions in pregnant animals.

For those dependent on livestock for food and income, the threat of an RVF outbreak among their herds is particularly serious.

“It can be devastating,” USAID Bureau for Humanitarian Assistance Senior Livestock Advisor Dr. Christine Jost said. “Imagine a farmer losing his entire crop that season, that’s along the lines of what we’re talking about when a herd becomes infected with RVF.”

In RVF-infected herds, 80-100% of pregnant sheep and cattle typically lose their offspring and 70-100% of young lambs and goats die from the disease.

These high livestock mortality rates can severely impact human livelihoods and nutrition due to reduced milk production, loss of income from livestock sales for food purchases, and lack of access to animal products and other food items if markets are impacted.

"Too late" to vaccinate animals against RVF once first cases are reported

Mosquitos carrying RVF typically start to infect herds about three weeks after the onset of heavy rains, and three weeks after that, herders begin to report significant numbers of cases in their herds.

Animal vaccines only offer protection about two weeks after they are administered, so governments, veterinarians, and animal health organizations must plan accordingly.

“There is a small window of time to safely vaccinate animals against RVF,” Jost noted.

In Kenya, The Ministry of Agriculture and Livestock Development recently issued an RVF outbreak alert through January 2024, and county governments are implementing RVF preparedness plans that include vaccination efforts. 

Because RVF spreads quickly – and due to limited veterinary services and resources for disease investigation – the first time authorities become aware of an outbreak is usually when human cases are reported, making it too late to prevent or mitigate the spread at the livestock source.

But even in instances when preventative measures are timed appropriately, veterinarians must take precautions when administering vaccines.

Governments are urging livestock owners to report any signs of RVF among their herds as soon as possible, even though previous events have shown that news of an outbreak can have its own detrimental effects on livelihoods and nutrition.

When an RVF outbreak occurred in Kenya and Somalia in 1998, Saudi Arabia banned livestock exports from the region for over a year. As a result, exports from Somalia, Ethiopia, Eritrea, Sudan, Kenya, and Djibouti dropped by more than 65% and approximately $100 million in revenue was lost.

“In a best case scenario we would like to see that governments are well prepared and livestock in susceptible areas are vaccinated before large numbers of mosquitoes begin to appear,” Jost said. “But even if an outbreak occurs, it is important that information, education, and communication campaigns are supported to keep herders informed so that they can protect themselves and their families.”

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