Are New Fungal Superbugs Emerging Thanks to Climate Change?

Candida auris fungus (source)

by Thomas Neuburger

Normally humans are not much troubled by fungal infections (as opposed to bacterial and viral diseases, which are far more common). There are several reasons for this — a healthy human's immune system being one — but another is that the temperature of the human body is simply too high to support most fungal life.

That seems to be changing, however, and the cause seems to be climate change — that increased global temperatures are forcing certain strains of fungi to adapt to warmer environments than they would normally find tolerable, thus making persistent fungal life in human and animal hosts much more possible.

An added wrinkle is that at least one of these fungi, Candida auris, is highly drug-resistant.

The layperson's version of the story comes from CNN ("Climate crisis might be behind the rise of mysterious superbug C. auris, study suggests"), but let's turn instead to this press release from the American Society for Microbiology, published at EurekAlert (emphasis added):

Washington, DC - July 23, 2019 - Global warming may have played a pivotal role in the emergence of Candida auris, according to a new study published in mBio, an open-access journal of the American Society for Microbiology. C. auris, which is often multi-drug resistant and is a serious public health threat, may be the first example of a new fungal disease emerging from climate change.

"The argument that we are making based on comparison to other close relative fungi is that as the climate has gotten warmer, some of these organisms, including Candida auris, have adapted to the higher temperature, and as they adapt, they break through human's protective temperatures," said Arturo Casadevall, MD, PhD, Chair, Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland. "Global warming may lead to new fungal diseases that we don't even know about right now."

C. auris emerged independently on three continents simultaneously, with each clade being genetically distinct. "What is unusual about Candida auris is that it appeared in three different continents at the same time, and the isolates from India, South Africa, and South America are not related. Something happened to allow this organism to bubble up and cause disease. We began to look into the possibility that it could be climate change," said Dr. Casadevall. "The reasons that fungal infections are so rare in humans is that most of the fungi in the environment cannot grow at the temperatures or our body." Mammalian resistance to invasive fungal diseases results from a combination of high basal temperatures that create a thermal restriction zone and advanced host defense mechanisms in the form of adaptive and innate immunity.

Dr. Casadevall concludes, "What this study suggests is this is the beginning of fungi adapting to higher temperatures, and we are going to have more and more problems as the century goes on. Global warming will lead to selection of fungal lineages that are more thermally tolerant, such that they can breach the mammalian thermal restriction zone."

The underlying study is here — "On the Emergence of Candida auris: Climate Change, Azoles, Swamps, and Birds" — and it's worth reading, especially the Abstract, introduction and conclusion.

The study's dry language, when parsed for its actual meaning, is frightening: "Widening of the geographic range of innately thermotolerant pathogenic fungi and the acquisition of virulence traits in thermotolerant nonpathogenic environmental fungi may shape the 21st century as an era of expanding fungal disease for both the fauna and flora of the planet."

Could a multidrug-resistant, hitherto unknown group of deadly superfungi reshape the 21st century? Hard to imagine it wouldn't.

Even those who expect to escape, via their great wealth and mobility, the climate crisis they have created may have a hard time escaping the pathogens their own pathology has spawned.

There's a kind of awful, symmetrical irony in that.