El Niño and Disease: Health Risks and How to Stay Safe
When heavy rain floods a neighborhood, the health effects can continue after the water begins to fall. Drinking-water supplies may become contaminated, families may lose access to health services, and conditions may become more suitable for mosquitoes. Elsewhere, unusually dry and hot weather can place pressure on water supplies, food availability and people's ability to stay cool.
El Niño can influence these conditions, but it does not directly cause an infection. Cholera needs the bacteria that cause cholera; malaria requires malaria parasites and the mosquitoes that transmit them. Weather can change the opportunity for exposure, while sanitation, housing, prevention and access to treatment influence what happens next.
This guide explains the main health risks to understand and practical steps families can take. It is especially useful for readers in tropical and flood-prone settings, including East Africa, but the diseases that matter most depend on local conditions.
What Is El Niño, and Why Can It Affect Health?
El Niño is the warm phase of a natural ocean–atmosphere cycle in the tropical Pacific. Its influence can change rainfall and temperature patterns far from the ocean itself. Some places become wetter; others experience drought or heat. The effect varies between events, seasons and locations.
The World Health Organization's ENSO fact sheet explains how these changes can affect water, food, air quality and disease transmission. A global El Niño announcement is a reason to prepare, not proof that a particular town will flood or experience an outbreak.
For decisions about travel, school attendance or evacuation, use local weather forecasts and public-health instructions.
Which Diseases and Health Problems Should You Watch For?
- Contaminated drinking water or food: cholera and other diarrhoeal diseases.
- Infectious mosquito bites: malaria or dengue where transmission occurs.
- Contact with contaminated floodwater: leptospirosis and wound infections.
- Infected livestock or mosquitoes in affected areas: Rift Valley fever.
- Extreme heat, smoke or disrupted food access: heat illness, breathing problems and undernutrition.
These are potential risks, not a prediction that all will occur together. Each has a different route of exposure and different prevention priorities.
1. Cholera and Other Diarrhoeal Diseases
Flooding can damage toilets and water systems, allowing sewage to enter water used for drinking or food preparation. Drought can also create problems when households have too little safe water for hygiene.
Cholera is an infection acquired through contaminated food or water. Severe cases cause profuse watery diarrhoea and dangerous fluid loss. Not every episode of diarrhoea is cholera, but rapid dehydration needs urgent attention regardless of the cause.
If someone develops watery diarrhoea, begin oral rehydration solution (ORS), mixed with safe water exactly as the packet instructs, while arranging care. Severe diarrhoea, repeated vomiting, very little urine, unusual sleepiness or inability to drink require urgent medical assessment. Do not delay treatment while trying home remedies.
Safe drinking water, sanitation and handwashing are central to prevention. Cholera vaccination may also be recommended by health authorities in affected settings.
Read WHO's cholera guidance .
What About Typhoid, Dysentery and Hepatitis A?
Unsafe food and water can transmit several infections, including typhoid and hepatitis A; some infections cause bloody diarrhoea or dysentery. These illnesses have different causes and may require different tests and treatment.
A persistent fever, blood in stool or yellowing of the eyes should be assessed by a health professional.
Food hygiene remains important even when a community has not reported cholera. Use safe ingredients and water, keep raw and cooked foods separate, cook thoroughly, and protect prepared food from contamination.
WHO's food-safety information explains why these habits matter.
2. Malaria
Malaria spreads through the bites of infected female Anopheles mosquitoes. In places where these mosquitoes and parasites are present, changes in rainfall and temperature can influence transmission. The relationship is not as simple as “more rain means more malaria.” Local habitats, mosquito control and access to treatment also matter.
Common symptoms include fever, chills and headache. A person with fever in a malaria-risk area should seek prompt testing and assessment instead of assuming the illness is malaria and taking leftover medicine.
Sleep under an insecticide-treated mosquito net where recommended, use suitable repellent according to its label, and reduce mosquito entry with screens. Pregnant women and young children need particular protection. Follow local malaria-prevention services and complete any prescribed treatment.
Difficulty breathing, confusion or seizures require emergency care.
See WHO's malaria fact sheet .
3. Dengue
Dengue is a viral infection transmitted mainly by infected Aedes mosquitoes. These mosquitoes are active during the day, so a bed net at night does not provide complete protection. Water collected in buckets, discarded containers and uncovered tanks can provide breeding sites.
Symptoms can include fever, headache, pain behind the eyes, muscle or joint pain and rash. Severe dengue may develop as the fever settles. Warning signs include severe abdominal pain, persistent vomiting, bleeding, rapid breathing or marked weakness.
Seek care if dengue is suspected. Avoid aspirin and ibuprofen because of bleeding risk; ask a clinician or pharmacist about appropriate fever treatment.
Empty and scrub water-holding containers regularly, cover stored water, and use daytime bite protection.
WHO provides further advice in its dengue fact sheet .
4. Leptospirosis After Floodwater Exposure
Leptospirosis is a bacterial infection associated with water or soil contaminated by urine from infected animals. Exposure can occur while wading through floodwater, cleaning affected areas or working around contaminated soil.
Illness may resemble other fever illnesses. Tell a health professional about recent floodwater or animal exposure if you become unwell; that history can help guide assessment.
The CDC advises watching for illness for 2–30 days after a flood and seeking care promptly if leptospirosis is suspected.
Avoid entering floodwater. When exposure cannot be avoided during necessary work, use waterproof protective clothing and boots, and cover cuts with waterproof dressings. Keep food and rubbish in closed containers to discourage rodents.
Read the CDC's flood-related leptospirosis advice .
5. Wound Infections and Injuries
Floodwater may hide broken glass, sharp metal, sewage and other hazards. Even a small cut can become infected after contact with contaminated water.
Wash exposed skin and minor wounds with soap and clean water. Seek medical care for deep or dirty wounds, embedded objects, increasing redness, swelling, pus or worsening pain. A clinician may need to review tetanus vaccination after an injury.
Children should not play in floodwater. Do not walk or drive across flooded roads: drowning and electrical hazards can be more immediate than infection. Protective boots do not make moving floodwater safe.
See the CDC's floodwater safety guidance .
6. Rift Valley Fever in Affected Livestock Areas
Rift Valley fever affects animals and people. Outbreaks in parts of Africa have been associated with heavy rainfall and increased mosquito populations. People can become infected through mosquito bites or contact with blood, organs or tissues from infected animals.
This risk is especially relevant to livestock keepers, veterinary workers and people involved in slaughtering or animal births. Avoid handling sick or dead animals without appropriate guidance and protection.
Do not drink raw milk or consume undercooked animal products. Report unusual livestock deaths or abortions to veterinary authorities.
The disease is not present in every flooded area. Follow local alerts rather than assuming an outbreak.
Read WHO's Rift Valley fever guidance .
7. Heat Illness, Breathing Problems and Food Insecurity
In places experiencing extreme heat, dehydration and heat illness can become serious concerns. Older adults, young children, outdoor workers and people with existing illnesses may need extra support.
Plan strenuous activities for cooler periods, rest in shade or a cooler building, and drink safe water regularly. People with prescribed fluid restrictions should follow individualized medical advice.
Confusion, collapse or seizures during heat exposure require emergency care and immediate cooling while help is arranged. Never give drinks to an unconscious person.
More information is available in WHO's heat-and-health guidance .
Dry conditions can also contribute to wildfire smoke, which can worsen breathing problems. Meanwhile, drought or flood damage can disrupt crops and access to food.
These are further reasons to prepare early and protect people who depend on regular medicines or nutritional support. El Niño's health effects extend beyond infectious disease.
A Practical Household Preparedness Plan
Make Drinking Water a Priority
Use a water source that authorities consider safe. If advised to boil water, bring clear water to a rolling boil for one minute, or three minutes above 6,500 feet (about 2,000 metres), then cool and store it in a clean covered container.
Follow the exact instructions for approved water-treatment products. Boiling does not remove fuel or toxic chemical contamination. If chemicals are suspected, obtain a different safe source.
Water that looks clear is not necessarily safe. The CDC's emergency water guide explains treatment options and their limits.
Plan for Food, Hygiene and Mosquito Protection
- Keep soap, safe water, ORS packets and essential medicines accessible.
- Store food covered and away from floodwater; discard food that is unsafe or contaminated.
- Prepare affordable meals using safe ingredients. For meal ideas, explore the Billy Blog TZ Recipe Index and apply the food-safety precautions above.
- Check mosquito nets and screens, cover stored water, and remove unnecessary containers that collect rainwater.
- Write down emergency contacts and decide how to reach care if the usual road becomes inaccessible.
Give each household member a simple responsibility: checking drinking water, keeping medicines together, monitoring official warnings or helping an older relative. A plan is more useful when everyone knows their part.
When Should You Seek Urgent Medical Help?
Get urgent medical help for:
- Difficulty breathing.
- Confusion, collapse or seizures.
- Severe diarrhoea with dehydration or inability to drink.
- Severe abdominal pain or persistent vomiting.
- Bleeding with fever.
- A rapidly worsening wound.
Tell the health worker about recent flooding, travel, mosquito exposure, unsafe water or contact with sick animals. These details can be as important as the symptoms themselves.
Frequently Asked Questions
Does El Niño Cause Cholera or Malaria Everywhere?
No. Weather can influence exposure and transmission, but infections also depend on the presence of pathogens, suitable vectors where relevant, and local living conditions. Community prevention and effective health services can reduce the risk.
Should I Take Antibiotics Before the Rains?
Do not start antibiotics or antimalarials simply because an El Niño event is announced. Preventive medicines are appropriate only for specific indications under professional guidance. Seek assessment if you become unwell.
Is This Article a Forecast for Tanzania?
No. It explains general health risks. For Tanzania, check current notices from the national meteorological service, the Ministry of Health and your local authorities. A seasonal outlook and a confirmed disease outbreak are different kinds of information.
Start with a realistic question: if water, transport or electricity were interrupted tomorrow, what would your household need first? Arrange safe water, protect essential medicines, check mosquito protection and agree on a route to care. These steps are useful before an emergency and remain valuable afterward.
This article provides general health education and does not replace individual medical assessment. Source links are provided throughout so readers can consult the original public-health guidance.
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