Candida auris, a species of fungus that grows as a yeast, was first discovered in the ear canal of a patient in Japan in 2009. Until recently, scientists considered it a mystery that C. auris popped up in more than 30 countries around the globe in just one decade.
The most perplexing and interesting thing about the fungus was its simultaneous emergence on three separate continents – in India, Venezuela, and South Africa – between 2012 and 2015 with each clade being genetically distinct.
Using isolates from 54 patients during 2012–2015 – whole-genome sequencing demonstrated that the isolates were grouped into unique clades by geographic region. Clades were separated by thousands of single-nucleotide polymorphisms, but within each clade, the isolates were clonal.
More thermally tolerant strains possible
In a study published Tuesday in mBio, an open-access journal of the American Society for Microbiology, researchers took a new look at the mysterious yeast, and now argue that Candida auris “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 co-author Dr. Arturo Casadevall, chairman of molecular microbiology and immunology at Johns Hopkins Bloomberg School of Public Health.
Fungal diseases are actually sort of rare in human beings. There are literally millions of species of fungi, while only a few hundred cause human disease. This is because of our high basal temperatures, which create a thermal restriction zone, and advanced host defense mechanisms in the form of adaptive and innate immunity.
So this means that the majority of fungi grow well in ambient temperatures (the temperature of the air surrounding an organism) and that only a small percentage of species can replicate at 37°C (98.6 degrees Fahrenheit). Two instances of this statement not being true would be the high prevalence of fungal infections in individuals with advanced HIV infection due to a weakened immune system, and white-nose syndrome in bats that occurs during their hibernation process when their temperature drops.
So humans have a thermal restriction zone that protects mammals. It is the difference between our high basal temperatures and the environmental temperatures. However, the new study notes that with the climate crisis anticipated to warm the Earth by several degrees in this century, this will reduce the thermal restriction zone or the margin between ambient and basal temperatures.
The study concludes that first of all, more information is needed because there may be other factors that have led to the emergence of this superbug and better surveillance systems are needed to track the spread of the organism.
However, the study also concludes: “Whether C. auris is the first example of new pathogenic fungi emerging from climate change or whether its origin into the realm of human-pathogenic fungi followed a different trajectory, its emanation stokes worries that humanity may face new diseases from fungal adaptation to hotter climates.”
