Extreme Weather Boosts Pathogens and Disease Spread, Study Finds

As climate change brings worsening heatwaves and other extreme weather, scientists are warning that these conditions are more suitable for pathogens to spread disease.

In a new study published in PLOS Climate, researchers investigated how heatwaves influenced a host, Daphnia magna or water fleas, and a parasite, Ordospora colligata. The team measured parasite fitness alongside varying amplitudes and durations of heatwaves.

“We manipulated the amplitude and duration of heatwaves across four average temperatures and four distinct time points at which the hosts were exposed to the pathogen,” explained Niamh McCartan, lead author of the study and a Ph.D. candidate at Trinity College Dublin. “This approach gave us 64 unique heatwaves for comparison.”

Through this experiment, the scientists found that heatwaves affected the parasite burden by up to 13 times, with less intense heatwaves allowing parasites to thrive while the most extreme heat decreased the number of parasites by also harming their hosts.

Based on the results, the team noticed that each factor of the heatwaves played a part in the parasite and host dynamic.

“And all these factors interact in different ways, to show that even the same heatwave that happens before you get infected might not have the same results as if it happened after you got infected,” said McCartan, as reported by Inside Climate News.

My comments with @lizagross.bsky.social in @insideclimatenews.org on a recent paper in @plosclimate.org insideclimatenews.org/news/0406202…

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— Prof Peter Hotez MD PhD DSc(hon) (@peterhotezmdphd.bsky.social) June 4, 2025 at 2:22 PM

While the study examined just one specific parasite and its host, the results could have widespread impact outside of the lab. For one, the host Daphnia magna is an important part of aquatic food webs, so increasing threats from the Ordospora colligata parasite could have rippling effects in nature.

Not only that, but heatwaves and other extreme weather could have similar effects for other parasites, including those that could spread diseases to crops and humans.

A 2022 study determined that already, 58% of infectious diseases for humans have been made worse by the impacts of climate change. Another study published in 2023 found that 69.3% of COVID-19 cases from summer 2022 would have been preventable if that summer did not experience heatwaves. 

McCartan also pointed out that climate change has also allowed disease-carrying mosquitoes to expand their range into areas that were previously too cold, further increasing risk of disease spread.

“The findings of our study highlight the urgent need to understand how warming and extreme weather events can alter disease dynamics more broadly.” McCartan said. “With all of this in mind, it’s important that future disease-specific models must account for fluctuating and extreme temperatures, not just averages.”