Climate Change Could Make Fungal Diseases Worse; How Does Heat Drive Genetic Changes in Mycelium?

Warmer climate may drive fungi to undergo mutations and become more dangerous to human health, a new study reveals.

Pathogenicity of Fungi

For most of modern history, fungal infections were not considered much of a threat in humans. There are known pathogenic fungi, like Aspergillus, Candida, and Cryptococcus, but they only affect immunocompromised individuals.

Although these microorganisms are known to cause vaginal itching, nail infections, and ringworms, fungal infections have been few. It has only slightly changed in recent years as health experts report cases of rare types of fungal infections.

Previous studies suggest that one of the reasons fungi have not been more of a threat is because they prefer cooler temperatures than those found on the bodies of mammals. According to the American Society for Microbiology, our internal temperature (37 degrees Celsius) is too hot for fungal species to tolerate. In addition, our innate immune cells can kill most fungal pathogens.

Climate-Driven Fungal Mutations

Just recently, a group of infectious disease specialists and medical researchers in China has found evidence that rising global temperatures cause genetic changes in pathogenic fungus. As the environment in which fungi live becomes warmer, they learn to adapt and may even reach a point where they will find the human body an ideal place to live.

In their study, the team looked for fungal infections in 96 hospitals in China from 2009 to 2019. Thousands of fungal strains have been found, including a previously undescribed invasive fungal pathogen Rhodosporidiobolus fluvialis. This strain was found in two unrelated cases and showed resistance to two of the most common types of therapies against fungal infections.

The researchers then injected laboratory mice with weak immune systems with blood that is infected with the same type of fungus obtained from the natural environment. They found that the fungus did not only thrive, but it also mutated into a more aggressive form. After exposing the pathogen to temperatures as high as 37 degrees Celsius, the fungus developed resistance to various antifungal agents.

A similar study was conducted by researchers from Duke University School of Medicine. In the paper "Genome-wide analysis of heat stress-stimulated transposon mobility in the human fungal pathogen Cryptococcus deneoformans," the researchers focused on Cryptococcus deneoformans which is known for being a globally distributed opportunistic fungal pathogen.

The authors discovered that raised temperatures can cause this pathogen to turn its adaptive responses into overdrive. This increases the number of genetic changes, some of which could lead to higher heat resistance or even greater disease-causing potential.

Led by Asiya Gusa, the research team found that higher heat makes the fungus' transposable elements to move around within the fungal DNA. This leads to the changes in the way Cryptococcus deneoformans use and regulate its genes. According to Gusa, these changes can even happen faster as heat stress speeds up the number of pathogenic mutations.

Unlike bacteria and viruses, fungi are transmitted from one person to another. However, their spores are present in the air and we breathe them all the time. Fortunately, our immune systems are well-equipped to fight these microorganisms.