In 2014 and 2015, NPR reported ona mysterious form of kidney diseasethat has killed tens of thousands in Central America, many of them in their 30s and 40s. Now there's a new theory about a possible cause.
Dr. Cecilia Sorensen in an editorial in the current issue of The New England Journal of Medicine calls this new mysterious form of kidney failure "a sentinel disease" in the era of climate change.
"We know that climate change is exacerbating a lot of different human diseases. It exacerbates cardiovascular disease, respiratory disease," says Sorensen, an emergency medicine physician who also teaches at the University of Colorado School of Medicine. "But this is one of the first identified where we can say this disease probably wouldn't have occurred if it weren't for the extreme global temperatures that we're seeing."
The disease, which has made kidney failure the second-leading cause of death in Nicaragua and El Salvador, was first reported in the 1990s. It was a strange new type of kidney failure. Sugar cane cutters from plantations in Nicaragua, El Salvador and Guatemala were turning up at clinics with end-stage kidney disease. Some had been in what seemed to be perfect health just a few years before. These laborers didn't have diabetes or hypertension or other factors that might explain why their kidneys were failing.
Among the early cases, almost all the patients did agricultural work on the low-lying plains near the Pacific Coast. Later the condition was also found among other people in the area, including miners, fishermen and workers in hot industrial plants. But most of the people dying from CKDu in Central America were relatively young farm laborers.
"Then we started realizing, wait a sec, there's a very similar disease process that's being described in India and Sri Lanka," Sorensen says.
And the question was, is it the same disease?
"Because it looks almost identical," Sorensen says. "It's affecting agriculture workers in hot areas. And there's also been reports of it happening in Africa as well as in the Middle East."
Adding to the difficulty of unraveling this mystery, CKDu appears to hit poor people in poor countries with poor health care systems. "So if the disease is there, we might not even know that it's there because no one's looking for it," Sorensen says.
Sorensen wondered if this deadly disease could be a result of global warming. But that's not easy to determine.
"It's very difficult to prove direct attribution and say this person is sick because of climate change," she says. "But what we can say is that this disease is occurring in parts of the world that are experiencing unprecedented warming, which we can attribute to climate change."
Climate change is just one of the theories behind what's causing CKDu. Most focus on heat stress and dehydration. Others propose a link to drinking water contaminated possibly with heavy metals or agricultural chemicals. Sri Lanka banned the herbicide glyphosate, sold under the brand name Roundup, over concerns that it was causing CKDu. Early on some health officials in Nicaragua blamed the epidemic on home-brewed alcohol.
Sorensen says there's probably not one single cause. In her words it's most likely "multi-factorial." But she goes back to the argument that this form of kidney failure is only happening in places that are hot and muggy — and getting hotter.
Neil Pearce, a professor of epidemiology at the London School of Hygiene and Tropical Medicine, has also been studying CKDu for years.
"It's a very unusual phenomenon. I've done work in this general area for 40 years, and it's very unusual to come across something like this," he says. But he's skeptical that climate change is the cause.
Pearce has been tracking workers in Nicaragua and found that over a two-year period some of them had lost a third of their kidney function.
"It may well be due to heat stress and the extremely bad working conditions in Central America. But adding on the link to climate changes is a bit tenuous," he says.
He doesn't think that the relatively small rise in global temperatures over the past few decades would cause such a significant shift in people's health. "We have to keep an open mind as to what could be the cause of the epidemic," he says.
Pearce also has looked for CKDu in other places with similar climatic conditions to Central America's Pacific coastal plains — northern Peru and Malawi, for example — and hasn't found it.
"If you go to south India there's these villages that are very close to each other, and some of them are getting CKDu and some of them are not. They're both equally hot, and they're not the hottest parts of India," he says. "Yes, there's something very strange going on. It's really interesting scientifically and obviously tragic in terms of the death and illness that it's caused."
Sorensen in her editorial doesn't claim to have the exact answer to what's causing CKDu. But she and just about everyone else studying this disease agree that it's related to hard physical labor in intense tropical heat. As global temperatures rise, she warns that health professionals should be thinking about how the changing climate might be driving what seem to be "mysterious" new ailments.
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