It’s official. July was the world's hottest month on record, scientists from the European climate monitoring agency confirmed on Aug. 8, a full 1.5°C (2.7°F) warmer than pre-industrial averages, offering a potent taste of what is to come in a world made hotter by climate change. The wildfires and heat waves that wreathed much of the northern hemisphere in smoke this summer? Expect more of the same. The surge in deaths and hospitalization from heat stress and stroke? Ditto. An increase in chronic kidney disease of non-traditional origin? Yup. Wait, what?
One of the enduring legacies of this summer’s spate of heat waves is likely to be a disease that few people have heard of, but which could become more prevalent as heat and humidity increase around the world. First documented in El Salvador’s sugarcane workers 21 years ago, Mesoamerican nephropathy, now known as Chronic Kidney Disease of Non-traditional origin (CKDnt), tends to manifest among outdoor laborers who work grueling hours in high heat conditions. Characterized by a fatal progressive loss of kidney function, CKDnt has killed at least 20,000 people in Central America since it was first diagnosed, and likely tens of thousands more elsewhere in the world. It’s been documented among rice farmers and salt harvesters in Thailand, Nepali migrant laborers in the Middle East and Malaysia, brickmakers and coconut harvesters in India, and in farmworkers and miners from Egypt to Cameroon—essentially anywhere in the tropical and equatorial latitudes that has the right combination of high heat, high humidity, and hard labor.
As temperatures increase around the globe, CKDnt cases are on the rise, contributing to what is arguably the world’s first occupational disease caused by climate change, one that, like a coal-miner’s black lung, can be prevented with the addition of workplace safety standards.
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Epidemiologist and CKDnt specialist Jason Glaser has no doubt that it is happening in the United States as well, especially after a summer that saw conditions in much of the country echo those of its neighbors to the south. “Absolutely everywhere we’ve looked that has that Venn Diagram of heavy work and high heat with poor labor protections, lo and behold, there it is.” The Biden Administration has tasked the United States Occupational Safety and Health Association with establishing federal heat safety standards to protect workers, but it is likely to be several years before they are implemented. The problem is that apart from a few clinical reports and case studies, no one is tracking it. That’s a grievous oversight, says Glaser, head of the CKDnt advocacy organization La Isla Network. “It’s so easy to prevent,” he says, yet with dialysis or kidney donation your only options, “so expensive to treat.”
The more typical form of kidney disease is either genetic or a consequence of diabetes, metabolic syndrome, or hypertension, and it largely affects an older population. CKDnt is closely tied to heat stress, and is more prevalent among outdoor laborers or miners who work in high heat conditions. While the causes are still debated, it appears to be triggered by an incidence of acute kidney injury—think extreme heat stress or heat stroke—and is exacerbated by continued exposure and dehydration. Studies in mice show that daily heat exposure and dehydration “can cause chronic tubulointerstitial disease with fibrosis and inflammation [scarring in the kidney’s small tubes], similar to what is observed in renal biopsies of subjects with Mesoamerican nephropathy,” according to a 2016 study published in the Clinical Journal of the American Society of Nephrology.
Doctor Farhad Modarai, the chief clinical officer for population health at Strive Health, which focuses on kidney care, notes that extreme weather caused by climate change is increasing the risk of acute kidney injuries across the United States. “Outdoor laborers are getting the brunt of the summer weather right now, with both excessive heat waves and air pollution accelerating dehydration and fatigue. Laborers that are sweating excessively due to these high temperatures are at higher risk for developing urinary tract infections or even kidney stones, which can lead to cumulative kidney damage.”
The wildfire smoke that choked much of the mid-and-eastern U.S. earlier this summer is an added stressor, says Modarai. The smoke carries microscopic particles that can reach the bloodstream, and, eventually, the kidneys, which can be damaged over time. “For any laborer who might already have kidney disease, dehydration caused by excessive heat and air pollution worsened by climate change could accelerate their disease progression, requiring them to depend on dialysis.”
According to Glaser, who has published several papers on the subject, approximately 8-10% of workers with acute kidney injury (AKI) will go on to develop CKDnt within 12 months; one AKI incident increases the risk of developing CKDnt five-fold within five years. “This is the black lung disease of today's outdoor laborers, and climate change is making it worse,” he says.
But without a public health database that tracks workers who have suffered heat-triggered kidney injuries over the years to find out how many go on to develop CKDnt, it will be nearly impossible to establish protocols for treatment, and compensation. “We really have to figure out how to create a better database of heat injury so we can figure out what's happening to people. We don’t want this to be the next CTE [chronic traumatic encephalopathy]. At least football players are well paid. These workers are earning nothing at all.”