'The most critically harmful fungi to humans': How the rise of C. auris was inevitable

Fifteen years ago, scientists discovered a new species of deadly, drug-resistant fungus: Candida auris. It is now considered one of the most dangerous fungal pathogens on Earth. In this excerpt from "What if Fungi Win?" (Johns Hopkins University Press, 2024), author Arturo Casadevall looks at the rise of this deadly fungus, which could be the first to have emerged as a result of climate change. 

In 2009, doctors at a hospital in Japan published a paper identifying a new species of fungus they'd found in the external ear canal of a 70-year-old patient. They called it Candida auris, with auris being the Latin word for ear. 

At first, it wasn't clear how much anyone should worry about this new discovery, if at all. Many new fungal species are reported in patients each year, but the overwhelming majority of these turn out to be isolated case reports, nothing worth panicking about. 

And C. auris laid low for a while, remaining an obscure unknown yeast in most parts of the planet — until it was found in hospitalized patients in all corners of the world, at roughly the same time. Strikingly, between 2012 and 2015, doctors in South Africa, Venezuela and on the Indian subcontinent simultaneously reported treating patients severely ill with what turned out to be C. auris infections (remember, no one had heard of this fungal species a few years earlier). 

With no contact or commonalities between them, these C. auris cases had appeared independently on three dif­ferent continents, with each fungus genetically distinct from the others. 

This meant that the usual suspect for fungal spread — our globalized world — wasn't at play here. Something new was afoot. It quickly became clear that this fungus was remarkably resistant to treatment. More than one in three patients with invasive C. auris infections in their blood were dying. In hospitals where this invasive fungal disease had been nonexistent, it was now a significant cause of death. 

To this day, C. auris remains mostly resistant to the antifungal treatments we have at our disposal, so once patients (and hospitals) become infected, it's nearly impossible to get rid of. Usually, doctors diagnose fungal infections after ruling out other sources, say, when a hospitalized patient has a fever that doesn't go away after treatment with antibiotics. Blood tests will likely indicate high white blood cell counts, another sign of an infection, but doctors often can't tell what type of microbe is doing the damage — or necessarily know how to treat it.