Climate hazards such as floods, heat waves and drought have exacerbated more than half of the hundreds of known infectious diseases in humans, including malaria, hantavirus, cholera and anthrax, a study says.
Researchers reviewed the medical literature of established diseases and found that 218 of the 375 known infectious diseases in humans, or 58%, appeared to be exacerbated by one of 10 types of extreme weather linked to climate change, according to a study in Monday’s journal Nature Climate Change .
Doctors, going back to Hippocrates, have long linked disease to the weather, but this study shows how widely the climate affects human health.
“If the climate changes, the risk of these diseases changes,” said study co-author Dr. Jonathan Patz, director of the Global Health Institute at the University of Wisconsin-Madison.
Doctors, like Patz, said they need to think of the diseases as symptoms of a sick soil.
“The findings of this study are frightening and well illustrate the enormous consequences of climate change on human pathogens,” said Dr. Carlos del Rio, an infectious disease specialist at Emory University, who was not part of the study. “Those of us in infectious disease and microbiology must make climate change one of our priorities, and we must all work together to prevent what will undoubtedly be a climate change disaster.”
In addition to looking at infectious diseases, the researchers expanded their search to look at all types of human diseases, including non-communicable diseases such as asthma, allergies and even animal bites to see how many diseases they could link to climate hazards in some way , including infectious diseases. They found a total of 286 unique diseases and of those, 223 of them appeared to be exacerbated by climate hazards, nine were reduced by climate hazards and 54 had instances of both exacerbated and minimized, the study found.
The new study does not do the calculations to attribute specific disease changes, odds or extent to climate change, but finds cases where extreme weather was a likely factor among many. The study mapped the 1,006 connections from climate danger to disease.
Study lead author Camilo Mora, a climate data analyst at the University of Hawaii, said the important thing to note is that the study is not about predicting future cases.
“There is no speculation here whatsoever,” Mora said. “These are things that have already happened.”
Mora knows one example firsthand. About five years ago, Mora’s home in rural Colombia flooded – for the first time in his memory there was water in his living room, creating an ideal breeding ground for mosquitoes – and Mora contracted Chikungunya, a nasty virus spread by mosquito bites. And although he survived, he still feels joint pain years later.
Sometimes climate change works in strange ways. Mora includes the 2016 case in Siberia when a decade-old reindeer carcass, dead from anthrax, was uncovered as the permafrost thawed from warming. A child touched it, got anthrax and started an outbreak.
Mora originally wanted to examine medical cases to see how COVID-19 intersected with climate hazards, if at all. He found cases where extreme weather both worsened and reduced the chances of covid-19. In some cases, extreme heat in poor areas caused people to gather to cool off and become exposed to the disease, but in other situations, heavy rains reduced the spread of COVID because people stayed at home and indoors, away from others.
Longtime climate and public health expert Kristie Ebi at the University of Washington warned that she was concerned about how the conclusions were drawn and some of the methods in the study. It is an established fact that the burning of coal, oil and natural gas has led to more frequent and more intense extreme weather, and research has shown that weather patterns are associated with many health problems, she said.
“However, correlation is not causation,” Ebi said in an email. “The authors did not discuss the extent to which the climate hazards assessed changed over the study’s time period and the extent to which changes have been attributed to climate change.”
But Dr. Aaron Bernstein, interim director of the Center for Climate, Health, and the Global Environment at the Harvard School of Public Health, Emory’s del Rio, and three other outside experts said the study is a good warning about climate and health for now and the future. Especially as global warming and habitat loss push animals and their diseases closer to humans, Bernstein said.
“This study underscores how climate change can load the dice to favor unwelcome infectious surprises,” Bernstein said in an email. “But of course, just reporting what we already know and what is still unknown about pathogens may be even more compelling about how preventing further climate change can prevent future disasters like COVID-19.”
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