The Link Between Climate Change and Drug-Resistant Fungal Infections

In a recent study on fungal diseases in Chinese hospitals, researchers discovered that two individuals were infected by a previously undocumented fungus affecting human health. Their findings were published in the journal Nature Microbiology. Scientists are worried that rising temperatures due to climate change could make fungi more dangerous to humans.

For a long time, scientists have been concerned that as Earth's temperature rises, fungi may become more harmful to people. It appears that Chinese experts have discovered evidence to back up that theory.

The pathogen was incurable with existing medications because it was already resistant to the two most popular anti-fungal medications. When exposed to higher temperatures, it rapidly became resistant to a third medication as well.

The finding “supports the idea that global warming may contribute to the evolution of this fungal pathogen or other new fungal pathogens,” said Co-Author Linqi Wang, a Microbiologist at the Institute of Microbiology of the Chinese Academy of Sciences.

This is a remarkable and truly unexpected finding, which bodes badly for the future.

David Denning, Infectious Diseases Researcher, University of Manchester

Denning was not involved in the study.

The human immune system is highly effective at combating infections, and fungi generally do not thrive at the high body temperatures of mammals. As a result, fungi cause fewer diseases in humans compared to bacteria or viruses. However, the HIV epidemic and immuno-suppressive medications over the past few decades have led to an increase in the number of individuals with compromised immune systems, resulting in a rise in the prevalence of fungal infections.

According to Asiya Gusa, a microbiologist at Duke University, many novel fungal diseases have recently emerged in humans. What is concerning, she adds, is that some of these illnesses are already drug-resistant.

A crucial question is whether elevated temperatures due to climate change could help fungi adapt to human body heat and become resistant to medications. According to a recent study, this adaptation does occur at times.

Between 2009 and 2019, researchers in China collected samples from patients in 96 hospitals as part of a program to identify fungi causing serious illnesses in humans. Among the thousands of fungal strains collected, one yeast strain, Rhodosporidiobolus fluvialis, had never before been reported to infect humans.

This yeast was isolated from the blood of two unrelated patients undergoing treatment for serious underlying illnesses in intensive care units: an 85-year-old woman from Tianjin who died in 2016 and a 61-year-old man from Nanjing who died in 2013. The pathogen showed resistance to both caspofungin and fluconazole, the two primary drugs used to treat potentially fatal yeast infections in humans.

To demonstrate that this fungus can infect mammals, researchers introduced it to mice with compromised immune systems. Unexpectedly, some of the fungus rapidly underwent a more aggressive form, which caused illness in the mice.

Upon investigating the possible cause, the researchers found that cells cultivated at 37 °C developed mutations 21 times more quickly than cells cultured at 25 °C.

According to a publication in Nature Microbiology, the researchers discovered that R. fluvialis developed drug resistance much faster when cultivated at 37 °C and exposed to another common antifungal, amphotericin B.

A new yeast pathogen which is antifungal-resistant, and can become increasingly resistant with higher temperatures, is remarkable.

David Denning, Infectious Diseases Researcher, University of Manchester

According to Johns Hopkins scientist Arturo Casadevall, fungi are cold-adapted organisms that are more likely to undergo mutations and changes due to a stress response caused by the temperature shift to that of the human body.

“We may have to start thinking of higher temperatures, such as those found in mammals, as a mutagen for fungi,” he said.

This could mean disastrous consequences if the world continues to get hotter due to global warming.

If fungi are responding to mammalian temperatures with genomic changes, then you can anticipate that similar events could happen during very warm days.

Arturo Casadevall, Scientist, Johns Hopkins University

If this is the case, then fungi may become less sensitive to medications and more aggressive due to climate change. This also increases the likelihood that they will adapt to higher temperatures and spread more easily to infect humans.

Gusa thinks it is too early to tell but expects more researchers to experiment with growing fungi at higher temperatures. She notes that while it is unlikely all fungi will start mutating more frequently, it is a concern if this pattern begins to repeat.

Fungal disease epidemiologist Matthew Fisher of Imperial College London does not currently see R. fluvialis as an emerging threat. He points out that humans rarely come into contact with related species, which have been found in the Dead Sea, the Baltic Sea, and Antarctic soil.