On the eve of Onam, the most joyous festival in India's Kerala state, 45-year-old Sobhana lay shivering in the back of an ambulance, drifting into unconsciousness as her family rushed her to a medical college hospital.
Just days earlier, the Dalit (formerly known as untouchables) woman, who earned her living bottling fruit juices in a village in Malappuram district, had complained of nothing more alarming than dizziness and high blood pressure. Doctors prescribed pills and sent her home. But her condition spiralled with terrifying speed: uneasiness gave way to fever, fever to violent shivers, and on 5 September - the main day of the festival - Sobhana was dead.
The culprit was Naegleria fowleri - commonly known as the brain-eating amoeba - an infection usually contracted through the nose in freshwater and so rare that most doctors never encounter a case in their entire careers. We were powerless to stop it. We learnt about the disease only after Sobhana's death, says Ajitha Kathiradath, a cousin of the victim and a prominent social worker.
In Kerala this year, more than 70 people have been diagnosed and 19 have died from the brain-eating amoeba. Patients have ranged from a three-month-old to a 92-year-old man.
Normally feeding on bacteria in warm freshwater, this single-cell organism causes a near-fatal brain infection, known as primary amoebic meningoencephalitis (PAM). It enters through the nose during swimming and rapidly destroys brain tissue.
Kerala began detecting cases in 2016, just one or two a year, and until recently nearly all were fatal. A new study has found only 488 cases have been reported globally since 1962 - mostly in the US, Pakistan, and Australia. And 95% of the victims have died from the disease.
But in Kerala, survival appears to be improving: last year there were 39 cases with a 23% fatality rate and this year, nearly 70 cases have been reported with about 24.5% mortality. Doctors say the rise in numbers reflects better detection, thanks to state-of-the-art labs.
Cases are rising but deaths are falling. Aggressive testing and early diagnosis have improved survival - a strategy unique to Kerala, said Aravind Reghukumar, head of infectious diseases at the Medical College and Hospital in Thiruvananthapuram, the state's capital. Early detection allows customised treatment: a drug cocktail of antimicrobials and steroids targeting the amoeba can save lives.
Scientists have identified around 400 species of free-living amoebae, but only six are known to cause disease in humans - including Naegleria fowleri and Acanthamoeba, both of which can infect the brain. In Kerala, public health laboratories can now detect the five major pathogenic types, officials say.
The southern state's heavy reliance on groundwater and natural water bodies makes it particularly vulnerable, especially as many ponds and wells are polluted. A small cluster of cases last year, for example, was linked to young men vaping boiled cannabis mixed with pond water - a risky practice that underscores how contaminated water can become a conduit for infection.
Kerala has nearly 5.5 million wells and 55,000 ponds - and millions draw their daily water from wells alone. That sheer ubiquity makes it impossible to treat wells or ponds as simple risk factors - they are the backbone of life in the state.
Some infections have occurred in people bathing in ponds, others from swimming pools, and even through nasal rinsing with water which is a religious ritual. Whether in a polluted pond or a well, the risk is real, says Anish TS, a leading epidemiologist.
So public health authorities have tried to respond at scale: in a single campaign at the end of August, 2.7 million wells were chlorinated.
Local governments have put up sign boards around ponds warning against bathing or swimming and evoked the Public Health Act to enforce regular chlorination of swimming pools and water tanks. But even with such measures, ponds cannot realistically be chlorinated - fish would die - and policing every village water source in a state of more than 30 million people is unworkable.
Officials now stress awareness over prohibition: households are urged to clean tanks and pools, use clean warm water for nasal ablutions, keep children away from garden sprinklers and avoid unsafe ponds. Swimmers are advised to protect their noses by keeping their heads above water, using nose plugs, and avoiding stirring up sediment in stagnant or untreated freshwater.
Yet, striking a balance between educating the public about real risks - of using untreated freshwater - and avoiding fear that could disrupt daily life is challenging. Many say despite guidelines issued for more than a year, enforcement remains patchy.
This is a difficult problem. In some places [hot springs], signs are posted to warn of the possibility of the amoebae in the water source. This is not practical in most situations since the amoebae can be present in any source of untreated water [lakes, ponds, pools], Dennis Kyle, a professor of infectious diseases and cellular biology at the University of Georgia, told the BBC.
In more controlled environments, frequent monitoring for proper chlorination can significantly reduce chances of infection. These include pools, splash pads, and other man-made recreational water activities, he said.
Scientists warn climate change is amplifying the risk: warmer waters, longer summers, and rising temperatures create ideal conditions for the amoeba. Even a 1C rise can trigger its spread in Kerala's tropical climate and water pollution fuels it further by feeding bacteria the amoeba consumes, says Prof Anish.
Dr. Kyle adds a note of caution, noting that some past cases may simply have gone unrecognised, with the amoeba not identified as the cause.
That uncertainty can make treatment even harder. Current drug cocktails are sub-optimal, Dr. Kyle explains, adding that in rare survivors, the regimen becomes the standard. We lack sufficient data to determine if all the drugs are actually helpful or needed.
Kerala may be catching more patients and saving more lives, but the lesson reaches far beyond its borders. Climate change may be rewriting the map of disease - and even the rarest pathogens may not stay rare for long.
