For the past three years we've been following the emergence and spread of a relatively recently identified fungal pathogen - Candida auris - which appeared nearly simultaneously around the globe (see Candida Auris: CDC July Update, COCA Call & EID Journal Study).
In absolute terms, the number of diagnosed infections remains small, but the rise of C. auris is of particular concern because:
The CDC issued a Clinical Alert to U.S. Healthcare facilities about the Global Emergence of Invasive Infections Caused by the Multidrug-Resistant Yeast Candida auris in 2016, but the first identified case was a decade ago in Japan.
- C. auris infections have a high fatality rate
- The strain appears to be resistant to multiple classes of anti-fungals
- This strain is unusually persistent on fomites in healthcare environments.
- And it can be difficult for labs to differentiate it from other Candida strains
Retrospective analysis has determined the first known cases appeared in South Korea in 1996 (cite). It has only been the past few years that its wider global spread has been recognized.Epidemiologists have been trying to account for the nearly simultaneous rise and spread of several closely related C. auris strains around the globe. The CDC's FAQ states:
How did C. auris infection spread globally?A new research letter, published last week in the CDC's EID Journal, detailed the finding of what appears to be a genetically distinct 5th clade of C. auris in Iran (see Potential Fifth Clade of Candida auris, Iran, 2018).
CDC conducted whole genome sequencing of C. auris specimens from countries in the regions of eastern Asia, southern Asia, southern Africa, and South America. Whole genome sequencing produces detailed DNA fingerprints of organisms. CDC found that isolates within each region are quite similar to one another, but are relatively different across regions. These differences suggest that C. auris has emerged independently in multiple regions at roughly the same time.
While there are a great many unanswered questions, authors
Briefly, that global warming has enabled a previously environmental C. auris fungus to adapt to higher temperatures. Those more heat-tolerant strains were able to infect wild birds - which spread the fungus far and wide to domesticated poultry - enabling it to jump humans, where it adapted to its new mammalian host.A series of events not unlike the transmission of influenza - which is native to birds - to humans and other mammals. The graphic below illustrates their hypothesis.
While none of this is set in stone - and it is unlikely to fully explain the rise of C. auris around the globe - it is nevertheless a intriguing hypothesis. Perhaps most importantly, if proven correct, it could presage the appearance of additional fungal threats down the road.
First stop, some excerpts from a press release from the American Society of Microbiology , followed by link to the full study (which you'll want to read in its entirety).
Rise of Candida Auris May be Blamed on Global Warming
July 23, 2019
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.”(Continue . . . .)
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.
Opinion/Hypothesis | Host-Microbe Biology
On the Emergence of Candida auris: Climate Change, Azoles, Swamps, and Birds
Arturo Casadevall, Dimitrios P. Kontoyiannis, Vincent Robert
James W. Kronstad, Editor
DOI: 10.1128/mBio.01397-19
ABSTRACT
(Continue . . )The most enigmatic aspect of the rise of Candida auris as a human pathogen is that it emerged simultaneously on three continents, with each clade being genetically distinct. Although new pathogenic fungal species are described regularly, these are mostly species associated with single cases in individuals who are immunosuppressed. In this study, we used phylogenetic analysis to compare the temperature susceptibility of C. auris with those of its close relatives and to use these results to argue that it may be the first example of a new fungal disease emerging from climate change, with the caveat that many other factors may have contributed.
