Hyderabad: The numbers tell a chilling story. Between January and September 19, Kerala reported 69 confirmed cases of amoebic meningoencephalitis, also commonly known as brain-eating bacteria. Nineteen patients have died. September alone saw 22 confirmed cases and nine deaths.
This surge represents an escalation from Kerala’s recent past.
Climate-driven health crisis
Between 2016 and 2022, the State recorded only eight cases total. But 2023 shattered that pattern with 36 infections and nine deaths. The acceleration has continued into 2024 and 2025, marking what experts now recognise as a climate-driven health crisis.
At the heart of this outbreak lies an uncomfortable truth: global warming is creating ideal conditions for Naegleria fowleri, the brain-eating amoeba that causes primary amoebic meningoencephalitis (PAM).
This free-living organism thrives in warm freshwater of lakes, rivers, hot springs and contaminated soil. As Kerala’s temperatures rise, these microscopic killers are finding increasingly hospitable environments across the State’s 44 rivers and countless water bodies.
The temperature connection
“The first reason is climate change,” states Dr TS Anish, a Nodal Officer at Kerala One Health Centre for Nipah Research and Resilience, Kozhikode.
“In our tropical climate, the baseline temperature may have risen by 1–2°C over the past few decades. As a result, surface water temperatures have also gone up.”
This seemingly modest temperature increase has profound biological implications. The seasonal pattern of infections reveals climate change’s fingerprints clearly across Kerala’s outbreak data.
“If you look at the data, the surge in cases of amoebic meningoencephalitis usually begins by late February, rises through the monsoon months and then declines by October or November when cooler weather sets in. This pattern keeps repeating, which shows that there are clear climatological links,” said Dr Anish.
The timing isn’t coincidental.
It directly correlates with Kerala’s warmest periods, when water temperatures reach levels that transform harmless amoebas into deadly pathogens.
The science of survival
Understanding how climate change enables these infections requires examining the amoeba’s life cycle. Naegleria fowleri is thermophilic, in common man language, heat-loving and becomes most dangerous at temperatures approaching 40°C.
“Pathogenic amoebas such as Naegleria fowleri and others are thermophilic—they thrive at higher temperatures, especially close to 40°C,” explained Anish.
"Climate change keeps them in their most active stage, known as the trophozoite form. In this stage, they feed, multiply, and can infect humans,” said Dr Anish.
Under normal conditions, these organisms can exist in three forms. The trophozoite form feeds and reproduces actively. The flagellated form doesn’t multiply. The cyst form remains dormant when conditions are unfavourable. Climate change disrupts this natural cycle.
“Normally, these amoebas can also exist in two other forms: a flagellated form, where they don’t multiply and a cyst form, which is dormant when food or conditions are unfavourable. But warmer water prevents them from shifting to those dormant or less active stages, keeping them infectious for longer,” said Dr Anish.
This extended infectious period means more opportunities for human contact with dangerous amoebas. The organisms remain in their most virulent state for longer periods throughout the year.
The ecosystem disruption
Rising temperatures don’t just energise harmful amoebas; they disrupt entire aquatic ecosystems in ways that favour pathogen growth.
“The second impact of rising temperatures is that they suppress other free-living organisms, the natural predators of these pathogenic amoebas. This indirectly allows the harmful amoebas to grow unchecked,” said Dr Anish.
This ecological disruption removes natural population controls that historically kept dangerous amoeba numbers manageable. Without predator pressure, pathogenic species can multiply rapidly in warming waters.
The temperature increases also boost the amoebas’ food supply.
"Third, higher temperatures also increase the presence of microorganisms like cyanobacteria, which serve as food for amoebas. This again boosts their survival,” said Dr Anish.
This creates a positive feedback loop. Warmer water increases cyanobacteria populations. More cyanobacteria means more food for amoebas. Better-fed amoebas reproduce more successfully, creating larger populations of potential pathogens.
Human behaviour and exposure
Climate change doesn’t just create more dangerous water—it drives more people into that water.
“And finally, when the weather is hotter, people are more likely to bathe or swim in ponds, pools, or other stagnant water bodies, increasing the risk of exposure,” explained Dr Anish.
This behavioural response to rising temperatures multiplies infection opportunities. As Kerala experiences more intense heat periods, residents naturally seek relief in available water bodies. Unfortunately, these same water bodies are becoming increasingly dangerous due to climate-enhanced amoeba populations.
The infection pathway remains consistent regardless of water source. Brain-eating amoeba “typically thrives in warm freshwater lakes, rivers, and hot springs. In rare cases, brain-eating amoeba has also been reported in people exposed to water in swimming pools which were not chlorinated properly,” said Dr Anish.
The organism enters through the nose and travels to the brain, where it destroys brain tissue.
“Early symptoms of PAM can include headache, fever, nausea, and vomiting, but the condition progresses rapidly, and many people with PAM die within 1 to 18 days after symptoms begin. It usually leads to coma and death after 5 days,” added Dr Anish.
Kerala’s geographic vulnerability
Kerala’s unique geography makes it particularly susceptible to climate-driven amoeba outbreaks. The state’s sizable forest cover and its intense monsoon pattern make it susceptible to outbreaks.
Specific regions show heightened vulnerability. Agrarian and forest-fringe areas like Wayanad, Idukki, Palakkad and Kozhikode are prone to such diseases along the backwater region Kuttanad in Alappuzha.
These areas combine multiple risk factors.
Forest cover creates numerous small water bodies. Agricultural activities can contribute to water contamination. Monsoon patterns create temperature and water chemistry fluctuations that may stress natural ecosystems.
The abundance of water bodies presents both blessings and curses. Experts also point out that with 44 rivers, water is both a boon and a curse for Kerala; it sustains life but also spreads disease if neglected.
Despite Kerala’s improved treatment protocols, the disease remains extraordinarily dangerous. Globally, the fatality rate is over 90 per cent, but in Kerala, it is relatively lower at under 30 per cent. However, it is still alarmingly high and has put the administration on its toes.
Health Minister Veena George emphasises progress while acknowledging challenges.
“The usual mortality rate among Amoebic Meningoencephalitis patients in developed nations is above 95 per cent. But our rate is much lower,” she said.