Why did C. auris emerge around the same time on different continents?
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In 2016, researchers published a study outlining the nearly simultaneous emergence of Candida auris on three continents.
To go along with our recent feature on fungal diseases, we asked Arturo Casadevall, MD, PhD, chair of molecular microbiology at the Johns Hopkins Bloomberg School of Public Health, why this happened.
C. auris is a new pathogenic fungus. It was first described in 2009, when it was isolated from the ear of a patient in Japan and thus called “auris,” which is Latin for ear. The greatest mystery in the story of the C. auris emergence is how did it appear suddenly on three continents — Africa, Asia and South America — during 2011 to 2013. Adding to the mystery is that the isolates from the three continents are each genetically different, indicating independent emergences and ruling out the scenario that the fungus was somehow brought from one region to another by human or natural activities.
When considering possible mechanisms for the three independent emergences, one must look for common factors, but these regions have different societies, cultures and climates. One common denominator is that all three regions are part of a planet that is in the midst of anthropogenic-driven global warming. Hence, I, along with colleagues Dimitrios P. Kontoyiannis, MD, PhD, ScD, MS, and Vincent Robert, PhD, proposed the hypothesis that C. auris emerged as a human pathogen as a consequence of adapting to warmer temperatures as a result of global warming. According to this view, C. auris was an environmental fungus that gained the capacity for growth at higher temperature as a result of warming climates, and this ability allowed it to cause disease in humans, whose average temperature is 98°F. In considering this explanation, it is important to also consider that warming climate is accompanied by an increased number of extremely hot days and that each such day provides a selection mechanism for fungal adaptation.
Consistent with this hypothesis, C. auris has now been recovered from the environment in the Andaman Islands, and some of the environmental isolates appear to struggle to grow at human temperature, suggesting that these are in the process of adapting to warmer temperatures. Scientists are working to validate or refute this theory by searching for more environmental sources and studying its mechanisms of heat adaptation in the laboratory.
References:
- Arora P, et al. mBio. 2021;doi:10.1128/mbio.03181-20.
- Casadevall A, et al. mBio. 2019;doi:10.1128/mbio.01397-19.
- Lockhart ST, et al. Clin Infect Dis. 2016;doi:10.1093/cid/ciw691.
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