When a mystery kidney disease killed more than 20,000 people in Central America over the course of a decade, it set alarm bells ringing in several tropical countries including India. The victims had similar profiles: They were young, their work involved hard labour and long hours in the sun.

Now a group of doctors has come together to reestablish an inconvenient truth: The world could be witnessing its first human epidemic directly linked to global warming. And India is one of the hotspots. Researchers have identified parts of the country with suspected sites of heat stress-associated nephropathy – a condition caused by dehydration and heat – and they include Andhra Pradesh, TN, Odisha, Goa and Maharashtra.

Chennai-based nephrologist Dr Georgi Abraham, part of the research team, said global warming was not even in the picture when they started the study, the results of which Clinical Journal of American Society of Nephrology has published.

“We just wanted to investigate why certain pockets had such high kidney ailments despite people not having diabetes, high blood pressure or obesity – the usual risk factors for kidney diseases,” said Dr Abraham.

After they ruled out metabolic factors and the possible presence of toxins, a study in Latin America gave the researchers their break. Several sugarcane farmers in Nicaragua were hospitalised with chronic kidney diseases. When doctors investigated, they linked the ailments to the practice of burning sugarcane during harvest.

“The high temperature caused the workers to sweat and they weren’t drinking enough water,” Dr Abraham said. “The heat and dehydration took a toll on the kidney.”

Closer home, a team from Jipmer, Puducherry, undertook a similar study on salt pan workers in the Union territory. They found the same result: Increased creatinine levels, signifying impaired kidney functioning or renal disease. Creatinine is a chemical waste product in the blood that passes through the kidneys, which filter it before the body eliminates it in urine.

Doctors also studied farmers in Andhra Pradesh, where a heat wave claimed more than 1,400 lives in a single month in 2015 because of the same causes. Some of the workers in that state also popped pills to ease body ache that added further pressure to their kidneys.