Into a deadly epidemic
the lab, where his team exposed mice to hours of heat. One group of mice was allowed to drink water throughout the experience, whereas a second group had water only in the evenings.
Within five weeks the mice with a restricted water intake developed chronic kidney disease. During the day, loss of salt and water caused the mice to produce high levels of fructose, and crystals of uric acid would sometimes form as water levels dropped in their urine. When the scientists disabled the gene that metabolises fructose and repeated the experiment, neither group developed chronic kidney disease.
The results caught GarcíaTrabanino’s attention: “I was astonished. His animal models were absolutely in line with our findings.”
The two investigated the effects of dehydration on Salvadoran field workers and found that levels of uric acid started high in the morning and increased throughout the day.
Johnson now believes that heat stress and dehydration drive the production of fructose and the hormone organisation relies on donations. Meanwhile, the number of people who need such treatment has continued to rise.
For Johnson, a clue to why the epidemic is escalating came from his fieldwork with García-Trabanino. One day, when researchers were measuring uric acid levels, only seven workers showed up for work. “But they all had uric acid crystals in their urine. It was bad news for these seven,” Johnson says.
He found out that it had been the hottest day of the year at the study location: “Suddenly a really, really big heatwave came in, and the workers weren’t ready.”
Johnson began to pore over global maps of climate and solar radiation. The rise in average temperatures over the past few years in Central America had been incremental, but the number of extreme events had gone up disproportionately.
“The areas that have the highest solar radiation and heatwaves are overlapping with the places right where the epidemics are.”
Climate experts at the National Oceanic and Atmospheric Administration in Boulder, Colorado, verified his discovery and published a report in May 2016, which suggested a connection between climate change and the epidemic. Johnson says it “may well be one of the first epidemics because of global warming”.
Climate change brings dire predictions of extreme weather but it is affecting the world’s most vulnerable now, he says. Our kidneys, with their role in keeping vital nutrients within the normal range and blood volume stable, may be on the front line of attack.
“We predict the kidney is going to be one of the prime targets as heat increases,” Johnson warns.
Researchers classify the new form of chronic kidney disease as “climate-sensitive”, which means that climate is one ingredient contributing to the epidemic.
As temperatures continue to rise, many such climate-sensitive diseases will become climatedriven, and monitoring and bringing attention to them will become even more crucial.
For the people of El Salvador, climate change is yet another lifethreatening obstacle to overcome amid the constant threat from not only frequent earthquakes and the volcanoes that dot the countryside, but also gang violence, political unrest and poverty.
But for García-Trabanino, the country’s perilous existence under towering volcanoes has come to symbolise what it means to be Salvadoran: “We have survived the civil war, earthquakes and volcanoes, but Salvadorans fight, and they will fight again.”