The patients do not look like the people doctors usually expect to see with kidney failure. They are often young, without diabetes or high blood pressure—otherwise healthy men doing physically demanding work: painting houses, roofing, paving roads, construction. Then their kidneys begin to fail. Some collapse at work. By the time they reach the hospital, they may need dialysis three times a week to stay alive.

The disease is called chronic kidney disease of unknown origin, or CKDu. In Central America it is also known as Mesoamerican nephropathy. And we still don't completely understand what causes it. That may be the part I find most unsettling.

CKDu has been devastating agricultural communities in Central America for decades, particularly among sugarcane workers in places such as El Salvador and Nicaragua. Researchers have investigated pesticides, heavy metals, contaminated water, infections, genetics and other possible causes. The evidence is complicated. But one factor keeps showing up: heat—more specifically, strenuous physical labor in extreme heat combined with repeated dehydration. Do that once and a healthy person may recover. Do it over and over, day after day, and those repeated small injuries may begin adding up. A 2019 article in the New England Journal of Medicine called CKDu a sentinel disease of the climate-change era. That description feels increasingly appropriate.

I want to be careful here. It would be easy to write climate change causes CKDu, but the science does not support saying that so simply. Researchers still disagree about the complete cause. Some evidence suggests heat and dehydration may be enough; others think heat is one part of a larger combination. So "unknown origin" still matters.

But we don't need to know the entire mechanism to recognize the problem created by a warming climate. If extreme heat contributes to kidney injury, then making extreme heat more frequent and more intense increases the number of opportunities for that injury to happen. Climate change doesn't have to invent an entirely new pathogen—it can change the environment enough that a disease once concentrated in particular occupations and regions begins appearing somewhere else. Texas may be showing us what that looks like.

There is another possibility in the Texas Monthly story that I had not considered. Some Central American immigrants may arrive with kidney damage that already began while working in hotter agricultural environments back home. Then they enter roofing, construction and other strenuous outdoor labor in Texas—increasingly hot Texas. Someone whose kidneys have already endured years of repeated injury may then spend another summer working on a roof in Houston. That is not much of a recovery plan.

When we talk about heat illness, the advice often becomes stay hydrated. That is good advice. It is not always something a worker controls. Texas Monthly describes workers whose employers severely restricted water breaks even during extreme heat. Studies among sugarcane workers have shown that improving access to water, rest, and shade can reduce kidney injury. We don't have to wait until researchers understand every molecular detail of CKDu before deciding that people performing heavy labor in 105-degree heat should be allowed to stop and drink water.

Then immigration policy makes the health problem harder to see. Many of the people most at risk have little access to health care—uninsured, undocumented, or afraid that interacting with institutions could expose them or their families to immigration enforcement. The population experiencing the disease may simultaneously be the population hardest to study. That is a terrible combination for an emerging public-health problem.

We still need to learn exactly what CKDu is. But we already know enough to take the heat seriously. A disease that spent decades devastating agricultural workers in Central America is now being recognized among workers in Texas. That does not mean climate change invented it. It may mean climate change is helping create more of the conditions in which it thrives. That is concerning enough.

Read the full Texas Monthly investigation.

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