Global warming may have played a critical role in the emergence of Candida auris, researchers reported in mBio.
C. auris, an often drug-resistant fungal pathogen, was first isolated in Japan in 2009 from the ear of an elderly patient, but it appears to have emerged simultaneously and independently on three separate continents, a fact that has puzzled experts.
In a recently published paper, Arturo Casadevall, MD, PhD, chair of the department of molecular microbiology and immunology at Johns Hopkins Bloomberg School of Public Health, and colleagues hypothesized that global warming may have induced C. auris — which they suggest may have been an environmental fungus before it became a human pathogen— to adapt to higher temperatures, making it easier for the fungus to infect people.
“We need to pay more attention to the fungal kingdom,” Casadevall told Infectious Disease News. “We are very remarkably resistant to fungal diseases. The reason for that is because we have advanced immunity and [a] high temperature. The combination of the two gives us phenomenal resistance because most fungi cannot grow in mammalian temperatures. But what would happen if more began to adapt to higher temperatures? That is, to me, the threat.”
Casadevall and colleagues explained that the Earth is expected to warm by several degrees in the 21st century, reducing the range between ambient temperatures and mammalian basal temperature.
According to the researchers, an analysis of the temperature range for C. auris demonstrated its ability to grow at higher temperatures compared with its nearest fungal relatives, implying that the fungus may have recently acquired its thermal tolerance, according to the study.
“It is noteworthy that the earliest description of C. auris came from a strain recovered from a human ear, which is much cooler than core body temperatures. Hence, this fungus may have gone through a short transient period during which it inhabited human surfaces before being associated with disease,” they wrote. “Currently, C. auris preferentially colonizes the cooler skin rather than the hotter gut mycobiome, a preference that may be consistent with a recent acquisition of thermotolerance.”
They noted that antifungal use has been suggested as a cause of C. auris’ emergence, but “reduced susceptibility to drugs and virulence are very different properties.” Explaining further, the researchers cited experience with aspergillosis resistance, which was a “well-known clinical entity” before the rise of resistance conferred from the agricultural use of azoles.
They also assessed the possibility that C. auris “recently acquired virulence traits that confer capacity for virulence,” but said it was “improbable” that this would occur on three continents at the same time “unless driven by another factor that selected for it.”
“They were different societies, different climates, different soils, different faunas, and yet, the one common denominator is they are all experiencing climate change,” Casadevall said. “They are all experience warming, and warming events could be selecting more heat-resistant organisms. More heat-resistant organisms mean more organisms that can defeat our heat wall, to put it in lay terms.” – by Marley Ghizzone
Disclosures: Casadevall reports no relevant financial disclosures.