El Niño and Mosquito-Borne Diseases: How Climate Drives Malaria, Dengue, and Outbreak Risk
Published: July 16, 2026 · 9 min read
TL;DR — How El Niño Fuels Disease Outbreaks
El Niño creates ideal conditions for mosquito-borne disease outbreaks through three distinct mechanisms. First, warmer temperatures accelerate mosquito development and virus replication inside mosquitoes — a 1°C rise can increase dengue transmission by 30%. Second, flooding from El Niño's heavy rains creates standing water breeding habitats. Third, drought forces households to store water in open containers, which become mosquito nurseries. The 2015-16 El Niño was linked to a major dengue surge in Brazil and Southeast Asia. The 1997-98 event triggered malaria epidemics in the East African highlands. With the 2026-27 event forecast as potentially stronger than both, the global health community is on alert for another cycle of amplified transmission.
Three Pathways: Temperature, Flooding, and Drought
El Niño amplifies mosquito-borne disease through three distinct but often overlapping pathways. Understanding them separately is essential for predicting which regions face elevated risk in a given event.
1. Temperature. Mosquitoes are cold-blooded. Their metabolism, biting rate, and reproduction all accelerate with temperature up to a threshold (roughly 32-34°C, above which they decline). The pathogens they carry — Plasmodium parasites for malaria, dengue virus, chikungunya virus — also replicate faster inside the mosquito at higher temperatures. The extrinsic incubation period (EIP) — the time between a mosquito ingesting a pathogen and becoming infectious — shrinks dramatically with warmth. For dengue, an EIP of 12 days at 25°C drops to 7 days at 30°C. A shorter EIP means more mosquitoes survive long enough to become infectious.
El Niño raises temperatures globally by releasing vast amounts of ocean heat into the atmosphere. The 2015-16 El Niño contributed to 2016 being the hottest year on record at the time. The warmer conditions expanded the altitude range of malaria transmission in the East African and South American highlands — areas where cooler temperatures had historically limited transmission.
2. Flooding. As described in El Niño Flooding: Which Regions Are Most at Risk, strong El Niño events bring heavy rainfall to Peru, Ecuador, the US Gulf Coast, East Africa, and other regions. Flooding creates standing water in urban and rural environments — puddles, blocked drains, flooded fields, tire tracks — that serve as mosquito breeding habitats. The most dangerous flood-associated disease is dengue, transmitted by Aedes aegypti, which breeds in clean standing water around homes.
3. Drought. Counterintuitively, drought can be as dangerous as flooding for mosquito-borne disease. When piped water supplies fail or become unreliable during drought, households store water in buckets, barrels, and cisterns. These open water storage containers are ideal breeding sites for Aedes aegypti, which has evolved to breed in artificial containers. The 2015-16 El Niño drought in Southeast Asia was followed by a major dengue surge — precisely because water storage increased.
Dengue: The Most El Niño-Sensitive Mosquito-Borne Disease
Dengue is the fastest-spreading mosquito-borne disease in the world, with cases increasing 30-fold in the last 50 years. It is also the disease with the best-documented El Niño connection. Multiple peer-reviewed studies have found that El Niño conditions correlate with increased dengue transmission across much of the tropics, with a lag of 2-6 months.
The mechanism is primarily temperature. Dengue virus replicates inside the Aedes aegypti mosquito at a rate that's strongly temperature-dependent. A 2019 study in PNAS found that the 2015-16 El Niño contributed to an estimated 20-30% increase in global dengue incidence compared to a neutral year. The study projected that under continued warming, El Niño-driven dengue surges will become more severe as the temperature baseline rises.
The 2023-24 El Niño provided a stark illustration. Brazil reported record dengue cases in early 2024 — over 6 million suspected cases, a 400% increase from 2023. While multiple factors contributed (including a new dengue serotype), the El Niño-driven warming was a significant amplifier.
For 2026-27, the risk is elevated because of the forecast event strength and the current global dengue situation. Several regions — including Brazil, Southeast Asia, and the Caribbean — are already experiencing high transmission. A very strong El Niño arriving during a high-baseline period could push case numbers to unprecedented levels.
Malaria in the Highlands
Malaria's El Niño connection is different from dengue's. While dengue risk increases across the tropics, malaria's strongest El Niño signal is in the highland regions of East Africa and South America — areas where transmission is normally limited by cold temperatures at altitude.
The mechanism is altitude-specific. During El Niño, warmer temperatures shift the "malaria belt" upward. The 1997-98 El Niño was linked to a dramatic increase in malaria cases in the Kenyan and Ugandan highlands (1,500-2,500 meters elevation), where hospitals reported 3-5 times normal caseloads. The populations in these highland areas have limited immunity to malaria because transmission is normally low, so when El Niño creates conditions for transmission, the result is explosive outbreaks with high mortality.
The 2015-16 El Niño repeated the pattern in Ethiopia and the Colombian Andes. In Ethiopia's highlands, malaria cases spiked 40% above the 5-year average. The pattern is clear enough that the WHO's Global Malaria Programme now incorporates ENSO forecasts into its seasonal malaria chemoprevention planning.
Chikungunya and Zika
Chikungunya and Zika, both transmitted by the same Aedes mosquitoes as dengue, show similar El Niño sensitivity — but with important differences. Chikungunya emerged as a major global health threat in the 2005-06 season and has since caused explosive outbreaks during El Niño periods. The 2014-16 El Niño saw chikungunya spread across the Americas for the first time, with over 1 million suspected cases.
Zika's relationship with El Niño was dramatically demonstrated in 2015-16, when the virus emerged in Brazil — during the peak of a very strong El Niño — and spread rapidly across the Americas. The link wasn't just temperature: the 2015-16 El Niño created drought conditions in northeastern Brazil (the epicenter of the Zika outbreak), which increased household water storage and created mosquito breeding habitat in a region where Aedes mosquitoes were abundant.
2026-27 Risk Map
Based on the forecast very strong El Niño and known ENSO-disease relationships, the following regions should be on alert for elevated mosquito-borne disease transmission during the 2026-27 period:
| Region | Primary Disease Risk | Driver | Peak Risk Period |
|---|---|---|---|
| Brazil (northeast) | Dengue, Zika, Chikungunya | Drought + water storage | Late 2026 - early 2027 |
| Southeast Asia | Dengue | Temperature + drought | Late 2026 |
| East Africa highlands | Malaria | Temperature lift | Early 2027 |
| Pacific Islands | Dengue | Temperature | Late 2026 |
| Peru / Ecuador coast | Dengue, Malaria | Flooding | Early 2027 |
| Caribbean | Dengue | Temperature + drought | Late 2026 |
| India / Sri Lanka | Dengue | Temperature | Late 2026 |
For more on El Niño's public health impacts, see El Niño and Human Health: Disease Outbreaks and Heat-Related Risks.
Explore more at the El Niño Guide — comprehensive climate science explained.