'Last of Us' Isn't Far Off — Warmer Weather May Increase Fungi Hazard

A new study reveals warmer weather could make fungi riskier to our health.

This has been a busy winter for urgent care clinics and hospitals as influenza took off earlier than usual, followed closely by a new highly transmissible SARS-CoC-2 variant, XBB.1.5, over the holidays. Although less commonly pathogenic in humans, fungi can also cause respiratory illness. HBO's "The Last of Us" depicts a post-apocalyptic society after a fungal infection caused by genus Cordyceps swept across the world. The infection introduces a world filled with cannibalistic characters similar to zombies. While the majority is fiction, there is some truth in the hit show.

Fortunately, in reality, healthy immune systems can fight fungi infections. As with many illnesses, those with a compromised immune system are at higher risk. And as medical advances improve longevity, the prevalence of people living with a weakened immune system may be increasing. New research from Duke University School of Medicine published in the Proceedings of the National Academy of Sciences suggests that higher temperatures trigger mutations in a fungus called Cryptococcus neoformans.

The investigators report that as our planet gets warmer, the number of genetic changes will increase. Warmer temperatures — due to global warming —promote the generation of transposable elements, also known as transposons or jumping genes. These transposons can swap places within the fungal DNA, creating variations in its genes. Transposons are quite common and account for approximately half the human genome and even more of the plant genome.

"These mobile elements are likely to contribute to adaptation in the environment and during an infection," says Duke School of Medicine postdoctoral researcher Asiya Gusa, Ph.D. "This could happen even faster," Gusa elaborates, "because heat stress speeds up the number of mutations occurring."

"These are not infectious diseases in the communicable sense; we don’t transmit fungi to each other," continues Gusa. "But the spores are in the air. We breathe in spores of fungi all the time and our immune systems are equipped to fight them."

"Mammals have the ability to regulate their own temperature, called endothermy," epidemiologist and biomedical communications consultant Allison Krug in Virginia Beach says. "Raising our body temperature through a fever is one way our immune system fights off invaders. Amazingly, cold-blooded ectotherms such as reptiles, fish, and insects also raise their body temperatures behaviorally," Krug explains, "by basking in the sun, swimming to warmer water, or increasing activity in the hive in the case of bees."

An increase in temperature is a common defense mechanism

"One of the first signs of illness may be a fever, but sometimes we develop a fever midway through a viral infection. This may be a sign of a secondary infection, perhaps a bacterial infection on top of a viral illness," Krug continues. "This elevation in body heat is how our body disrupts an invading microorganism — the inflammatory response makes the body less hospitable for growth and is a call to action for the key players of our immune system."

Researchers are interested in how heat-stabile certain fungi have become, and whether that increases the ability of the fungi to withstand the human body’s natural defenses. By continuing to study patients with recurring fungal infections we can better understand the evolution of pathogenic fungi and how we can treat illness.

Although this is an interesting field of research, and the television show may be headline-generating, there is no immediate cause for alarm. In fact, the topic of heat-stabile fungi has been under investigation for over a decade. "This research suggests one way that fungi may be adapting to live at higher temperatures as the climate changes," Krug says.

"If warmer temperatures encourage transposon activity, and this leads to adaptations which help fungi live in humans," continues Krug, "then our immune systems will continue the process of responding with new adaptations to fight the fungi. It will be interesting to follow this research."