El Niño Rains Raise Rift Valley Fever Threat Across Eastern Africa as Disease Risk Spreads

El Niño-driven heavy rainfall and flooding are expanding conditions favourable to Rift Valley fever transmission across Eastern Africa, prompting FAO and IGAD to call for urgent surveillance and preparedness measures. With six countries facing the highest assessed risks and transmission conditions expected to worsen through January 2027, the warning exposes the challenge of preventing climate-sensitive disease outbreaks before they threaten livestock, livelihoods and human health.

Heavy rainfall associated with El Niño is creating conditions for Rift Valley fever to spread across Eastern Africa, raising concerns over livestock health, human exposure and the region's capacity to prevent outbreaks. The Food and Agriculture Organization of the United Nations (FAO) and the Intergovernmental Authority on Development (IGAD) are urging governments to strengthen disease surveillance, prepare vaccines and coordinate preventive action as environmental risks intensify.

The warning comes as climate forecasts indicate expanding conditions suitable for virus transmission between October 2026 and January 2027. Ethiopia, Kenya, Somalia, South Sudan, Tanzania and Uganda face the highest assessed risks, while Burundi and Rwanda are experiencing increasing exposure. The geographical spread highlights a difficult preparedness challenge: disease threats are emerging across multiple territories before outbreaks are necessarily detected.

Unlike emergencies that become visible through confirmed infections, the current concern is largely predictive. Rising rainfall, flooding and mosquito breeding opportunities are signalling where transmission could occur. Whether those warnings translate into effective prevention will depend on how quickly animal health, public health and environmental authorities organize their response.

When Extreme Rainfall Creates a Regional Disease Threat

Rift Valley fever is a viral disease that infects livestock, including sheep, goats, cattle, buffaloes and camels, and can also affect humans. Mosquitoes are major transmitters, while contact with infected animals or animal products provides another route of human infection. Livestock movements can further extend the disease's geographical reach, complicating efforts to contain transmission.

The connection between climate conditions and disease risk is particularly pronounced during periods of intense rainfall. Flooding expands mosquito breeding habitats, potentially increasing transmission opportunities across livestock populations. Simultaneously, severe weather can disrupt veterinary services, creating difficulties for disease detection and preventive interventions when surveillance becomes most urgent.

Current El Niño conditions have drawn comparisons with 1997–1998, when Eastern Africa experienced one of its largest recorded Rift Valley fever epidemics and animal outbreaks. The historical parallel underscores the potential seriousness of the environmental warning, although comparable rainfall patterns do not establish that another epidemic of similar magnitude will occur.

Forecasts indicate particularly intense precipitation across southern Ethiopia, Kenya and central and southern Somalia, with more than a 90 percent probability of rainfall exceeding 400 millimetres. Wetter-than-normal conditions are also expected across Burundi, Rwanda, South Sudan, Uganda and Tanzania, increasing the geographical extent of environments potentially favourable to disease transmission.

The threat extends beyond mainland Eastern Africa. Risks are increasing in the Comoros, northern Madagascar, Mayotte, south-western Saudi Arabia and western Yemen, although these areas currently face lower assessed risks. Such geographical differences reinforce the importance of distinguishing between widespread climatic exposure and the varying levels of disease risk within individual territories.

Why Forecasting Disease Is Only Half the Preparedness Challenge

The expanding warning is being informed by FAO's Rift Valley Fever Early Warning Decision Support Tool, which combines satellite observations, climate forecasts, disease surveillance information and expert assessments. The platform identifies locations with elevated environmental risk up to three months ahead, creating opportunities for preventive action before infections become widespread.

Its October 2026 assessment places Tanzania first in terms of geographical area classified as suitable for RVF transmission, followed by Ethiopia, Kenya, South Sudan and southern Sudan. Newly suitable environments have emerged in southern Somalia, Rwanda and Burundi. Continued heavy rainfall could expand these areas further, including into additional parts of Uganda.

Environmental suitability, however, is not equivalent to confirmed infection. Forecasting systems identify conditions that could enable transmission, rather than measuring actual disease prevalence. Their effectiveness depends on connecting early warnings with field surveillance capable of identifying infections and supporting timely responses.

FAO and IGAD are calling for risk-based monitoring, advance positioning of vaccines and essential supplies, and improved coordination between neighbouring countries. These measures address different elements of the threat: identifying emerging transmission, ensuring preventive resources are accessible, and reducing delays when disease risks cross administrative boundaries.

The warning also demonstrates the operational value of FAO's Emergency Prevention System for Animal Health, known as EMPRES. Through more than three decades of disease monitoring, forecasting and risk communication, the system has supported countries in anticipating animal health threats. Its current role illustrates how environmental intelligence can inform preparedness across geographically dispersed risk zones.

An important uncertainty remains the extent to which predictive warnings can be matched by national response capacity. Forecasts indicate where attention is needed, but they do not establish vaccine availability, veterinary service readiness or surveillance coverage in individual countries. Those operational factors will influence how effectively governments can act on the expanding risk assessments.

Livestock Movements and Human Exposure Complicate the Response

The challenge extends beyond controlling a mosquito-borne livestock disease. Rift Valley fever connects animal infections with human exposure, creating overlapping responsibilities for veterinary and public health institutions. Livestock-dependent communities face potential threats to animal health and livelihoods, while people handling infected animals or animal products may encounter additional infection risks.

FAO and IGAD are emphasizing a One Health response that integrates animal, human and environmental health systems. This approach reflects the disease's interconnected transmission pathways: rainfall affects mosquito habitats, mosquitoes can infect livestock, and infected animals can expose humans. Monitoring these relationships separately risks overlooking developments relevant to several sectors simultaneously.

Cross-border livestock movements introduce another dimension. Infected animals can contribute to geographical spread, while rainfall and flooding may create favourable transmission environments across neighbouring territories. Therefore, coordinated surveillance and information-sharing become essential elements of regional preparedness rather than matters confined to individual national health systems.

The coming months will test whether early warnings produce timely preventive measures. Updated climate projections, changing transmission suitability maps, surveillance findings and vaccination preparations will provide important indications of how the regional threat is evolving. Particular attention will be needed where newly suitable environments emerge or expand under continued rainfall.