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How climate change could make fungal diseases worse

Fungal diseases in general are appearing in places they have never been seen before & previously harmless or mildly harmful #fungi are turning deadly for people. A likely reason for this worsening fungal situation, scientists say, is #climate change.

Back at the turn of the 21st century, Valley fever was an obscure fungal disease in the United States, with fewer than 3,000 reported cases per year, mostly in California and Arizona. Two decades later, cases of Valley fever are exploding, increasing more than sevenfold and expanding to other states.

And Valley fever isn’t alone. Fungal diseases in general are appearing in places they have never been seen before, and previously harmless or mildly harmful fungi are turning deadly for people. One likely reason for this worsening fungal situation, scientists say, is climate change. Shifts in temperature and rainfall patterns are expanding where disease-causing fungi occur; climate-triggered calamities can help fungi disperse and reach more people; and warmer temperatures create opportunities for fungi to evolve into more dangerous agents of disease.

For a long time, fungi have been a neglected group of pathogens. By the early 2000s, researchers were already warning that climate change would make bacterial and viral infectious diseases like cholera, malaria and dengue more widespread. “But people were not focused at all on the fungi,” says Arturo Casadevall, a microbiologist and immunologist at the Johns Hopkins Bloomberg School of Public Health. That’s because, until recently, fungi haven’t troubled humans much.

Our high body temperature helps explain why. Many fungi grow best at around 12 to 30 degrees Celsius (roughly 54 to 86 degrees Fahrenheit). So, while they find it easy to infect trees, crops, amphibians, fish, reptiles and insects — organisms that do not maintain consistently high internal body temperatures — fungi usually don’t thrive inside the warm bodies of mammals, Casadevall wrote in an overview of immunity to invasive fungal diseases in the 2022 Annual Review of Immunology. Among the few fungi that do infect humans, some dangerous ones, such as species of Cryptococcus, Penicillium and Aspergillus, have historically been reported more in tropical and subtropical regions than in cooler ones. This, too, suggests that climate may limit their reach.

Fungi on the move

Today, however, the planet’s warming climate may be helping some fungal pathogens spread to new areas. Take Valley fever, for instance. The disease can cause flu-like symptoms in people who breathe in the microscopic spores of the fungus Coccidioides. The climatic conditions favoring Valley fever may occur in 217 counties of 12 US states today, according to a recent study by Morgan Gorris, an Earth system scientist at the Los Alamos National Laboratory in New Mexico.

But when Gorris modeled where the fungi could live in the future, the results were sobering. By 2100, in a scenario where greenhouse gas emissions continue unabated, rising temperatures would allow Coccidioides to spread northward to 476 counties in 17 states. What was once thought to be a disease mostly restricted to the southwestern US could expand as far as the US-Canadian border in response to climate change, Gorris says. That was a real “wow moment,” she adds, because that would put millions more people at risk.

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