CNN  — 

It began in 2009, when doctors in Tokyo swabbed the ear of a 70-year-old woman and found an unknown strain of fungus that can infect humans and, in severe cases, cause a blood infection in high-risk patients. It’s called Candida auris.

Now, a decade after it was discovered, cases have been reported in more than 30 countries around the globe – including the United States, Australia, India, Germany, Israel, Venezuela and South Africa, according to the US Centers for Disease Control and Prevention.

But how we got here is a mystery: While the fungus seems to have cropped up relatively recently, its genetics reveal distinct groups that evolved apart, on different continents.

“We really can’t explain that … unless it goes back thousands of years,” said Dr. Tom Chiller, chief of the CDC’s Mycotic Diseases Branch.

But when scientists went looking for C. auris in old samples – knowing that earlier tests may have misidentified it or not picked it up – it was hardly anywhere to be found.

“It’s a bit of a paradox, really,” said Dr. David Eyre, an infectious disease physician based at Oxford University. “Why has it suddenly come to cause a problem at a similar time in different parts of the world?”

Could it have to do with our use of antibiotics and antifungal drugs? Changes in the health care environment? Or perhaps it’s some other evolutionary change, experts wonder.

“We’ve got an estimated 5 to 6 million different species of fungi. Only a few hundred cause human disease,” Chiller explained. “So there’s a ton of potential for more things to emerge.

“Why did this Candida emerge?”

A fungus that acts ‘like a bacteria’

To Chiller, the emergence of C. auris highlights the danger of antimicrobial resistance: the rise of “superbugs” that threaten to render many of our tried-and-true drugs powerless. But there’s something different about this fungus.

“It’s a yeast that’s acting like a bacteria,” he said.

Other species of Candida already travel with us – on our skin, in our guts – and they don’t tend to cause infections unless there’s an imbalance. This can happen, for example, when antibiotics wipe out good bacteria with the bad, leaving a place for Candida to grow.

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