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In 2009, a new fungus was found in Tokyo, swabbed from a woman’s ear. In 2016, it was detected for the first time in the U.S., at a hospital in New York. Today, it’s been found in 28 states and the District of Columbia. 

Candida auris infected just over 2,300 people in the U.S. in the past year and has been spreading at an “alarming rate,” according to the Centers for Disease Control.

Early research suggests rising global temperatures, a byproduct of climate change, may have helped it evolve to live inside the human body. But the fungus’ origins remain a mystery—where it emerged and why it did so suddenly are still unclear.

“Right now we don’t have a smoking gun,” says Luis Ostrosky, chief of infectious diseases and epidemiology at UTHealth Houston and Memorial Hermann. But climate change, he adds, is “a likely theory.”

Here, scientists explain what they know about Candida auris, how climate change may have brought about its rise in hospitals, and why it may not be the last of its kind. 

Some fungal infections are common, like athlete’s foot, but infections from Candida auris are more rare and start from inside the body, multiplying in the blood or festering in a preexisting wound. 

Infections primarily occur in people who are already immunocompromised and receiving regular medical treatments where they might come into contact with something like an infected IV. 

“You’re not going to get Candida auris in the gym, and your kids are not going to get it at school, but if you’re a patient with frequent contact with the healthcare system, you should be aware of this,” says Ostrosky. 

What makes Candidas auris so concerning is that it’s difficult to detect and even harder to treat. Standard blood tests, the most common way to test for the infection, miss the fungus 50 percent of the time, says Ostrosky. Larger, more research-oriented hospitals and universities have newer tests that can detect genetic material from fungus in blood, but Ostrosky says these tests are difficult to find elsewhere. 

When it is detected, it’s often resistant to antifungal treatments, and spores can live on surfaces outside the body for weeks. This means even if you kick the fungus, you can be reinfected. The CDC estimates that about 30 to 60 percent of people who have been infected with this fungus have died, but they note many victims also had preexisting medical conditions.

Ostrosky thinks the recent surge in these infections may have resulted from staff and supply shortages during COVID-19 surges when some hospitals had to take measures like reusing protective equipment.

The human body is usually too hot for fungi to survive. But as climate change makes average temperatures rise and heat waves more common and extreme, fungi might be capable of evolving to withstand hotter temperatures in the environment, and therefore more likely to survive inside us. That’s the theory scientists have for how Candida auris may have seemingly emerged overnight. 

One paper published in 2019 hypothesized that the fungus emerged as a human health threat simultaneously on three different continents. 

Arturo Casadevall, an infectious disease expert at Johns Hopkins suggests the common denominator is warming temperatures around the world. 

“We proposed it may be the first fungal pathogen that emerged from climate change,” he says. 

Another 2019 paper authored by CDC scientists suggested climate change was a plausible explanation for Candida auris’s emergence, but one that couldn’t be confirmed without more research.

In August, researchers in Austria urged “concerted global action” in response to the outbreak. “These challenges are a serious reminder of our persisting vulnerability against infectious diseases, and certainly, we will have to face and handle comparable menaces in future,” they wrote.

For years scientists have been warning that climate change will alter weather patterns and raise temperatures so drastically that new diseases are likely to emerge. 

In the years since Candida auris was first detected in Japan, scientists have documented more evidence of fungal infections in particular spreading because of more extreme weather.

Hurricane Harvey, a major hurricane whose extreme rains were supercharged by climate change, hit Houston in 2017 and exposed residents, including those who were immunocompromised, to deadly mold left growing on the storm’s soggy debris. On the west coast of the U.S., a fungal infection known as Valley Fever is spreading north. Drier conditions caused by the region’s megadrought are helping carry fungal spores farther. 

“The possibility of greater mutations in response to heat stress is a real concern,” says Asiya Gusa, a molecular geneticist at Duke University. “The environmental fungi we’re more concerned with are ones we breathe into our lungs as spores in the air.”

In research she and her colleagues published in January, Gusa studied  Cryptococcus deneoformans, a fungus commonly found in soil—a fungus whose infection can result in potentially fatal meningitis in the brain or pneumonia in the lungs. Gusa’s team observed that when the fungus was heated from 86°F to 98°F, genes found throughout the fungus’s DNA were more likely to jump around and mutate, movement that hints at an ability to adapt.

While the study was an early look at how the fungus behaves in a lab, Gusa says results could be a warning with broader implications

“[The study] suggests fungi might adapt more quickly in warming temperatures than we anticipated,” says Gusa. “It really was alarming.”

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