Can El Niño floods bring Rift Valley fever, cholera and dengue to Kenya?

Kenya's Ministry of Health and the World Health Organization (WHO) both tie heavy rain to cholera, dengue and Rift Valley fever, and Rift Valley fever outbreaks in Kenya in 1997–98 and 2006–07 came after heavy rain. The ministry lists cholera, typhoid, other diarrhoeal diseases, malaria, dengue fever and Rift Valley fever among the dangers of the October–December rains, The Standard reported on 15 September. The Kenya Meteorological Service Authority (KMSA), formerly the Kenya Meteorological Department, forecasts a 99 per cent probability of above-normal rainfall for the season.

Celeste Saulo, Secretary-General of the World Meteorological Organization (WMO), said on 8 October that El Niño is “firmly established and strengthening rapidly”, potentially one of the strongest since at least 1950. The WMO expects it to peak in December.

Cholera is caused by consuming food or water contaminated with the bacterium Vibrio cholerae. WHO's fact sheet of 29 September 2026 links the disease to limited access to safe water and sanitation, and names floods, cyclones and drought among the climate events behind that. Symptoms appear 12 hours to five days after infection, and WHO says most people can be treated successfully with prompt oral rehydration solution (ORS), the drink of water and salts that replaces lost fluid.

Rift Valley fever travels through animals and mosquitoes. WHO's fact sheet of 20 December 2024 calls it a viral disease that mainly affects animals, with severe illness in cattle, sheep, camels and goats. Most human infections come from contact with the blood or organs of infected animals, and mosquito bites can also pass it on. WHO says outbreaks in Africa are “closely associated with periods of above-average rainfall”, and that a major outbreak hit Kenya, Somalia and Tanzania in 1997–98 after El Niño and extensive flooding. The virus was first identified in 1931, during an epidemic among sheep in Kenya's Rift Valley.

A study of the 2006–07 outbreak, published by Anyamba and colleagues in the Proceedings of the National Academy of Sciences on 14 January 2009, describes how flooding sets it off. The team combined satellite readings of ocean temperature, rainfall and vegetation into risk maps; the paper says this gave a two- to six-week warning for the Horn of Africa, calls it the first prospective prediction of a Rift Valley fever outbreak, and says field investigations later confirmed the predictions. The authors report that flooding of dambos, shallow grassland that fills seasonally, hatches infected Aedes mcintoshi mosquito eggs lying dormant in the soil, and that Culex mosquitoes later colonise the flooded ground.

Kenya reported 684 human cases, including 155 deaths, between 30 November 2006 and 12 March 2007, WHO said in May 2007, and the authors of the 2009 paper suspect the outbreak was more widespread than reported. The paper gives the first case, in Garissa, an estimated onset date of 30 November 2006; mosquito surveillance there had begun in late November, weeks before human cases were reported.

Dengue is spread mainly by the Aedes aegypti mosquito, WHO's fact sheet of 21 August 2025 says, and high rainfall and humidity are among the factors behind its spread. There is no specific treatment; WHO advises covering, emptying and cleaning household water storage containers every week.

The Intergovernmental Authority on Development (IGAD) Centre for Pastoral Areas and Livestock Development, working with the Food and Agriculture Organization (FAO), has named Kenya among eight countries at heightened risk of Rift Valley fever, the Somalia-based news site Dawan Africa reported on 10 August. It urged livestock keepers to report unusual livestock deaths and abortions promptly to veterinary authorities and to avoid unsafe handling of sick or dead animals.

The ministry's list of at-risk areas includes the northern and north-eastern counties of Mandera, Wajir, Marsabit and Garissa; the coastal counties of Lamu, Kilifi, Kwale, Tana River, Taita Taveta and Mombasa; the Kano Plains in Kisumu County; and Budalang'i in Busia County, according to the Kenyan news site Kenyans.co.ke. During the 2023–24 El Niño, 43 of Kenya's 47 counties were affected, and cases of cholera, Rift Valley fever and malaria rose.

For households, the ministry advises drinking safe water by boiling or treating it when its safety is uncertain, washing hands with soap and safe water before preparing or eating food and after using the toilet, and keeping children away from floodwater. Families should stock oral rehydration salts, and anyone with severe symptoms should seek medical care immediately.