Dangerous fungal infections are on the rise, and a growing body of research suggests warmer temperatures might be a culprit.
The human body’s average temperature of 98.6 degrees Fahrenheit has long been too hot for most fungi to thrive, infectious-disease specialists say. But as temperatures have risen globally, some fungi might be adapting to endure more heat stress, including conditions within the human body, research suggests. Climate change might also be creating conditions for some disease-causing fungi to expand their geographical range, research shows.
“As fungi are exposed to more consistent elevated temperatures, there’s a real possibility that certain fungi that were previously harmless suddenly become potential pathogens,” said
Peter Pappas,
an infectious-disease specialist at the University of Alabama at Birmingham.
Deaths from fungal infections are increasing, due in part to growing populations of people with weakened immune systems who are more vulnerable to severe fungal disease, public-health experts said. At least 7,000 people died in the U.S. from fungal infections in 2021, the Centers for Disease Control and Prevention said, up from hundreds of people each year around 1970. There are few effective and nontoxic medications to treat such infections, they said.
Photos: What We Know About Deadly Fungal Infections
In the video game and HBO show “The Last of Us,” a fungus infects people en masse and turns them into monstrous creatures. The fungus is based on a real genus, Ophiocordyceps, that includes species that infect insects, disabling and killing them.
There have been no known Ophiocordyceps infections in people, infectious-disease experts said, but they said the rising temperatures that facilitated the spread of the killer fungi in the show may be pushing other fungi to better adapt to human hosts and expand into new geographical ranges.
A January study in the journal Proceedings of the National Academy of Sciences showed that higher temperatures may prompt some disease-causing fungi to evolve faster to survive.
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Researchers at Duke University grew 800 generations of a type of Cryptococcus, a group of fungi that can cause severe disease in people, in conditions of either 86 degrees Fahrenheit or 98.6 degrees Fahrenheit. The researchers used DNA sequencing to track changes in the fungi’s genome with a focus on “jumping genes”—DNA sequences that can move from one location on the genome to another.
Asiya Gusa, a study co-author and postdoctoral researcher in Duke’s Molecular Genetics and Microbiology Department, said movement of such genes can result in mutations and alter gene expression. In fungi, Dr. Gusa said, the movement of the genes could play a role in allowing fungi to adapt to stressors including heat.
Dr. Gusa and her colleagues found that the rate of movement of “jumping genes” was five times higher in the Cryptococcus raised in the warmer temperature.
Cryptococcus infections can be deadly, particularly in immunocompromised people. At least 110,000 people die globally each year from brain infections caused by Cryptococcus fungi, the Centers for Disease Control and Prevention said.
Candida auris, a highly deadly fungus that has been reported in about half of U.S. states, also appears to have adapted to warmer temperatures, infectious-disease specialists said.
“Fungi isn’t transmitted from person to person, but through fungal spores in the air,” Dr. Gusa said. “They’re in our homes, they’re everywhere.”
An analysis published last year in the journal Clinical Infectious Diseases said some potentially deadly fungi found in the soil, including Coccidioides and Histoplasma, have significantly expanded their geographical range in the U.S. since the 1950s. Andrej Spec, a co-author of the analysis and an associate professor of medicine at Washington University School of Medicine in St. Louis, said warming temperatures, as well as other environmental alterations associated with climate change, could have played a role in this spread.
Cases of Coccidioidomycosis or Valley fever, a disease caused by Coccidioides, were once mostly limited to the Southwest, Dr. Spec said. Now people are being diagnosed in significant numbers in most states. Histoplasma infections, once common only in the Midwest, have been reported in 94% of states, the analysis said. Histoplasma is also spread through bat droppings and climate change has been linked to changing bat migration patterns, Dr. Spec said.
The World Health Organization has identified Cryptococcus, Coccidioides, Histoplasma and Candida auris as being among the fungal pathogens of greatest threat to people.
“We keep saying these fungi are rare, but this must be the most common rare disease because they’re now everywhere,” Dr. Spec said.
Write to Dominique Mosbergen at dominique.mosbergen@wsj.com
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