Fungi: Updates on Our Friends and Foes

“Climate change is creating conditions conducive to the emergence of new fungal pathogens and is priming fungi to adapt to previously inhospitable environments, such as polluted habitats and urban areas, leading to the geographical spread of some fungi to traditionally non-endemic areas.”

Danila Seidel, PhD, University of Cologne, et al The Lancet (June, 2024)

“The psilocybin experience can help us access parts of ourselves that are normally hidden from view.”

Paul Stamets, American mycologist, author and advocate of medicinal fungi

Fungi, bacteria, archaea, viruses and parasites are the five types of microbes I have featured in my Germ Gems posts.  Fungi may be the most unusual of these, in part, because some fungi, namely mushrooms, aren’t even microscopic.

In today’s post, I feature members of the mushroom genus Psilocybe that produces the psychedelic drug psilocybin—a drug that looks increasingly promising for treatment of certain mental health disorders—as well as two increasingly nasty thermotolerant fungal species Candida auris and Coccidioides immitis.    

Fun fungi facts. A fungus is any member of the group of eukaryotic organisms—a group that includes yeasts and molds, as well as the more familiar mushrooms. There are an estimated 3.5-5.1 million fungal species on Earth but only 300 fungal species are human pathogens.

Most fungi are either harmless or beneficial to humans. The fungus Penicillium chrysogenum is responsible for penicillin, the first “miracle drug” that is estimated to have saved over 200 million lives.  Some foods and beverages are derived from fungi. For example, yeasts produce bread, beer, wine, and related products. And the morel mushroom is considered by some to be “the most delicious of all fungi.” 

Moreover, the largest living organism on Earth is a fungus—Armillaria ostoyae. Much larger than the largest animal on Earth, the Antarctic blue whale, the humungous fungus Armillaria ostoyae is found in Oregon, spreads out across 10 square kilometers, and is still growing. (For more fun facts about fungi, check out paleontologist Richard Fortey’s book Close Encounters of the Fungal Kind.)

Therapeutic uses for psychedelic mushrooms? Psilocybin is a chemical in certain types of mushrooms. Also known as “shrooms,” these psychedelic mushrooms grow on nearly every continent and have a long history of use in traditional ceremonies.

In the U.S., psychedelics are considered illegal under the Controlled Substances Act. (Native American ceremonial use of peyote is protected under federal regulation in at least 28 states.) Nonetheless, some people use shrooms recreationally or, allegedly, to improve their mental health.

In 2017, the Food and Drug Administration, granted “breakthrough therapy” designation for the psychedelic MDMA for post-traumatic stress disorder. In 2018, the agency granted the same designation for psilocybin for treatment-resistant depression. These designations helped allow psychedelic research to progress.

Researchers still have much to learn about psilocybin’s potential medical uses. But researchers at the National Institutes of Drug Abuse, along with other groups of scientists, are now evaluating psilocybin as a potential clinical treatment for alcoholism, nicotine addiction, substance use disorders, and mental illnesses, such as depression and anxiety—including end-of-life anxiety.

And then there’s the gut. Another area of research dealing with the beneficial roles of fungi in human health is in the “mushrooming” research field of the gut microbiome. Although far less is known about fungi found in the gut (known as the mycobiome) than bacteria residing there, studies to date suggest that some fungi participate in signaling of the brain. (See, “The Mycobiome: A Neglected Component in the Microbiota-Gut-Brain Axis,” Microorganisms 2018).

Fungal pathogens. It is estimated that in 2024, deaths from fungal diseases exceeded 3.75 million people. And every year, that number increases. (I addressed the alarming increases in fungal diseases in “Fungi Are on the Move,” Germ Gems, February 15, 2023 and in “Mounting Threat of Fungal Pandemics: The Case of Candida Auris,” Germ Gems, April 3, 2024.)

Climate change (global warming) has contributed to the worldwide increase in cases of the emerging fungal pathogen C. auris. Danila Seidel and colleagues reviewed this phenomenon in The Lancet. (See, Seidel, D. et al., “Impact of climate change and natural disasters on fungal infections, The Lancet, June 2024). They suggested that this evolutionarily favorable development for fungi called thermotolerance was also playing an important role in the escalating number of cases of the fungal disease, coccidiomycosis—aka, “cocci” and “Valley Fever”—in the deserts of the Southwest.

In 2024, the number of cases of Valley Fever in Arizona was up almost 50% and, according to a California tally published in January 2025, cases had tripled since 2022. (See, Wichman, M., “Dust Devil,” Science, January 16, 2025, detailing the frightening increase in cases of coccidiomycosis).

An emerging sexually transmitted fungal infection. On November 13, 2024 in MDEdge, medical journalist Heidi Splete reported that the Centers for Disease Control and Prevention (CDC) had identified four cases of infection due to the fungal dermatophyte Trichophyton mentagrophytes genotype VII (TMVII) as a cause of sexually transmitted genital tinea infection. Although TMVII is known in Asia and Europe, these were the first cases reported in the U.S., and, to my knowledge, the first fungal sexually transmitted disease.

This skin infection is transmitted through direct skin-to-skin contact of men who have sex with men (MSM). It can be mistaken, however, for eczema or psoriasis. The CDC therefore recommends that skin lesions that fail to respond or worsen with the application of topical steroids can be a red flag for TMVII, especially in the setting of MSM.

What we can expect. Human behavior (mainly misbehavior) plays a pivotal role in most, if not all, emerging infections, including those caused by fungi. If we fail to curtail global warming, we can anticipate increases in infections that are facilitated by heat. Up until now, that’s been largely certain vector-borne and water-borne infections. With the debuts of C. auris and TMVII infections, and the worsening of infections caused by C. immitis, we can add fungi to the list.

The climate change-driven fungal fitness and virulence of both C. auris and C. immitis are warning signs for humans to act. We need to address global warming in a meaningful way. Unless something significant is done to curb climate change, we can expect evolution to favor the emergence of other thermotolerant fungi.