Heavy rainfall and flooding associated with El Niño are significantly increasing the risk of Rift Valley fever (RVF) outbreaks across Eastern Africa, the Food and Agriculture Organization of the United Nations (FAO) and the Intergovernmental Authority on Development (IGAD) have warned, calling on affected governments to strengthen preparedness and surveillance without delay.

RVF is an acute viral disease that affects livestock — including sheep, goats, cattle, buffaloes and camels — and can also infect humans. The virus is transmitted mainly by mosquitoes, while humans can also become infected through direct contact with infected animals or animal products. FAO and IGAD note that the current El Niño is approaching record strength, with conditions described as comparable to those observed in 1997–98, when one of the largest recorded RVF epidemics and epizootics struck Eastern Africa.

The countries currently assessed as facing the highest risk are Ethiopia, Kenya, Somalia, South Sudan, Tanzania and Uganda. Risk is also increasing in Burundi and Rwanda, while lower but growing risks exist in the Comoros, northern Madagascar, the Department of Mayotte, south-western Saudi Arabia and western Yemen.

According to FAO's RVF Early Warning Decision Support Tool (RVF DST), conditions suitable for RVF transmission are expected to increase across much of Eastern Africa between October 2026 and January 2027. Tanzania currently has the largest area classified as suitable for transmission, followed by Ethiopia, Kenya, South Sudan and southern Sudan. New suitable areas have emerged in southern Somalia, Rwanda and Burundi, with further expansion expected in Uganda as the rainy season continues.

The heaviest rainfall is forecast for southern Ethiopia, Kenya, and central and southern Somalia, where there is a greater than 90 percent probability of receiving more than 400 mm of rainfall. Burundi, Rwanda, South Sudan, Uganda and Tanzania are also expected to experience wetter-than-normal conditions. Drier-than-normal conditions are forecast for southern Sudan and across Southern Africa.

FAO and IGAD are calling on affected countries to strengthen risk-based surveillance, pre-position vaccines and essential supplies, and enhance cross-border and cross-sector coordination through a One Health approach. The alert was issued through FAO's Global Early Warning and Prevention System for Animal Health (FAO-EMPRES), which has monitored and forecast animal disease threats for more than 30 years.

The RVF DST integrates satellite data, climate forecasts, disease surveillance information and expert analysis to identify areas at elevated outbreak risk up to three months in advance. Combined with ongoing livestock movements, expanding mosquito habitats could make surveillance and outbreak response more challenging, FAO and IGAD said.

This article is based on a primary source and has undergone editorial review prior to publication.