In recent years, the fungus Candida auris has emerged as a growing public health threat. The infection is usually serious and tough to treat effectively. The fungus lurks in hospital settings, can be challenging to diagnose and is often misidentified. As such, the Centers for Disease Control and Prevention is trying to stop it from spreading. Reporting in the open-access journal mBio, researchers have suggested that the fungus is on the rise because of warmer temperatures in our environment.
"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," explained Arturo Casadevall, MD, Ph.D., 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."
Genetic studies showed that while the fungus arose on three different continents at the same time, they are different from one another. "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 Casadevall.
Mammals have high body temperatures, which can help protect us from fungal infections that can't tolerate the pressures it faces from the immune system, or the heat that's found in mammals (but not usually in the environment). "The reasons that fungal infections are so rare in humans is that most of the fungi in the environment cannot grow at the temperatures [of] our body," added Casadevall.
This work assessed how susceptible C. auris was to temperature compared to fungal relatives with phylogenetic similarity. C. auris was found to be more tolerant of higher temperatures than its relatives; C. auris could grow at temperatures found in mammalian bodies while most of the other fungi could not. This indicated that as global temperatures have risen, C. auris has changed, and thrived.
"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," explained Casadevall. "Global warming will lead to selection of fungal lineages that are more thermally tolerant, such that they can breach the mammalian thermal restriction zone."
If we can improve our methods for identifying emerging threats, we might be able to find novel fungal infections before they become widespread, which might have been possible for C. auris if we had better tools in place.
"We need to make investments in better surveillance of fungal diseases. We are pretty good at surveilling influenza and diseases that cause diarrhea or are contagious, but fungal diseases are not usually contagious and therefore nobody has really bothered to document them well," noted Casadevall. "If more fungi were to cross over, you really wouldn't know until somebody started reporting them in the literature."