India at growing risk of infectious diseases due to climate change effects

Climate change is altering the conditions that infectious diseases need. Rising heat, unusual rainfall, floods and droughts can affect pathogen survival, insect populations and contact between people, animals and contaminated environments. This makes outbreaks harder to predict and control.

For example, flooding can overwhelm sewage systems and mix human and animal waste into water supplies. Warmer water and air can help pathogens survive longer. Floods can also drive rats from sewers into homes, raising the risk of leptospirosis. Mosquitoes may survive and breed for longer in warmer conditions.

India is already seeing changing disease patterns. Hepatitis A, hepatitis E and cholera, once concentrated in particular seasons, have been reported more frequently throughout the year. The IPCC expects heatwaves and extreme rainfall to increase, so health experts say prevention must become part of climate planning, not just emergency response.

A 2025 study by IPE Global and Esri India projects a sharper extreme-weather burden by 2030. It estimates that heatwaves could double in major Indian cities, while extreme rainfall events could increase by 43% across the country. These figures describe projected weather changes, not a guaranteed number of disease outbreaks.

The health concern is that extreme conditions can reshape disease ecology. Heat may help pathogens survive longer and allow mosquitoes to breed for longer. Intense rainfall can flood homes, overwhelm sewage systems and carry contaminated water into communities. It can also drive disease-carrying animals from hiding places.

The projections matter because recent disease patterns are already becoming less predictable. Health experts argue that India should factor climate-related outbreaks into planning and prevention. The IPCC likewise warns that heatwaves and extreme rainfall events are projected to increase in coming years.

Extreme weather changes the environmental conditions that control infection. Heat can help some pathogens survive longer and can extend the breeding season of mosquitoes. Floods spread contaminated water and waste. Erratic rainfall can disrupt familiar seasonal disease patterns. Droughts can bring people, livestock and wildlife closer together around limited water sources.

The article gives several examples. Heavy rain can overwhelm sewage systems, mixing human and animal waste into water supplies. Flash floods can drive rodents from sewers and burrows, while their urine contaminates water, food and surfaces. Warmer conditions may also help mosquitoes persist in places previously too cold for them.

These pathways increase the chance of outbreaks in new locations and at unexpected times. Cholera, hepatitis A and E, leptospirosis, dengue, malaria and Zika are among the diseases discussed. A Chennai study found gastrointestinal hospitalisation risk was 60% higher during the 15 days after extreme rainfall.

Several diseases in the article are connected to changing weather, but they do not all spread in the same way. Cholera and hepatitis A and E can spread when sewage or waste contaminates water. Leptospirosis spreads through water or soil contaminated by urine from infected animals, especially rats. Dengue, malaria and Zika are associated with mosquitoes.

Flooding explains several links. It can overwhelm sewage systems and carry contamination into homes and water supplies. It can also drive rats from sewers and burrows. Warmer temperatures may help pathogens survive longer and allow mosquitoes to live and breed for longer. Shifting rainfall can change where these vectors persist.

The article reports that leptospirosis cases peak during and immediately after the monsoon. It also describes malaria-carrying Anopheles mosquitoes surviving at higher, previously colder elevations in the Himalayan foothills. Pune reported increased Zika infections after heavy monsoon rains and flooding in 2024.

The health impact after extreme weather can be substantial, even beyond visible destruction. A Chennai study found that the risk of hospitalisation for gastrointestinal illnesses was 60% higher during the 15 days after an extreme rainfall event. This shows how quickly illness can rise after flooding or intense rain.

Kerala’s 2018 flood provides another measure. Integrated Disease Surveillance Project data recorded 1,318 leptospirosis cases, including 53 deaths, after the flood. Flooding can drive rats from sewers and burrows. Their urine may contaminate water, food and surfaces, allowing Leptospira bacteria to reach people.

These figures do not represent every extreme-weather event, but they show the possible scale of harm. The article also notes that leptospirosis has a strong monsoon link, with more than 85% of annual cases occurring during and immediately after the monsoon. Risks can therefore extend beyond the initial disaster.

Poor drainage and sewage systems make climate-related outbreaks worse because they cannot safely manage sudden, intense rainfall. Floodwater may then remain in homes, streets and communities, mixing with sewage and animal waste. Inadequate sanitation can increase contact with contaminated water, food and surfaces. Poor urban planning can place homes and infrastructure in areas vulnerable to flooding.

The article describes the mechanism directly. Heavy rain can overwhelm sewage systems and allow waste to enter water sources. Flash floods can drive rats out of sewers and burrows. Their urine can contaminate water, food and surfaces, increasing leptospirosis risk, particularly during city floods.

This is especially important as extreme rainfall is projected to rise 43% across India by 2030. The source does not quantify the separate effects of drainage, sanitation or planning failures, but established public-health evidence shows that stronger water, sanitation and drainage systems reduce exposure. Prevention therefore needs infrastructure and disease surveillance, not only treatment after outbreaks begin.

Pathogens are agents that cause disease, including the bacteria discussed in the article. Disease vectors are living carriers, such as mosquitoes, that can spread pathogens between hosts. Zoonotic diseases move between animals and people. These categories overlap: Leptospira bacteria cause a zoonotic disease, while rats are important hosts and contaminated environments help transmit it.

Flooding shows how the pathways connect. Rats may leave sewers and burrows, and their urine can contaminate water, food and surfaces. People then encounter the bacteria. Mosquitoes provide another route. Warmer conditions and changing rainfall can alter their breeding, behaviour and distribution, potentially expanding transmission of dengue, malaria and Zika.

The environment can therefore act as a bridge among animals, pathogens and people. Climate change may change that bridge by affecting pathogen survival, vector range and human-animal contact. The article reports Anopheles mosquitoes persisting at elevations in the Himalayan foothills that were previously considered too cold.