A pathogen that resists almost all of the drugs developed to treat or kill it is moving rapidly across the world, and public health experts are stymied how to stop it.

By now, that’s a familiar scenario, the central narrative in the emergence of antibiotic-resistant bacteria. But this particular pathogen isn’t a bacterium. It’s a yeast, a new variety of an organism so common that it’s used as one of the basic tools of lab science, transformed into an infection so disturbing that one lead researcher called it “more infectious than Ebola” at an international conference last week.

Maryn McKenna (@marynmck) is an Ideas contributor for WIRED, a senior fellow at the Schuster Institute for Investigative Journalism at Brandeis University, and the author of Beating Back the Devil, Superbug, and Big Chicken. She previously wrote WIRED’s Superbug blog.

The name of the yeast is Candida auris. It’s been on the radar of epidemiologists only since 2009, but it’s grown into a potent microbial threat, found in 27 countries thus far. Science can’t yet say where it came from or how to control its spread, and hospitals are being forced back into old hygiene practices—putting patients into isolation, swabbing rooms with bleach—to try to control it.

To a medical system that’s been dealing with worsening antibiotic resistance for decades, this chronology feels somewhat familiar: just another, potentially tougher battle to face. But the struggle to keep this resistant yeast from surging is a warning sign that relying on standard responses won't work. As the foes continue to evolve, medicine needs both new tech, and surprisingly old techniques, to fight its microbial wars.

As the foes continue to evolve, medicine needs both new tech, and surprisingly old techniques

“This bug is the most difficult we’ve ever seen,” says Dr. Tom Chiller, the chief of mycotic diseases at the CDC, who made the Ebola remark at the 20th Congress of the International Society for Human and Animal Mycology in Amsterdam. “It’s much harder to kill.”

The center of the emerging problem is that this yeast isn’t behaving like a yeast. Normally, yeast hangs out in warm, damp spaces in the body, and surges out of that niche only when its local ecosystem veers out of balance. That’s what happens in vaginal yeast infections, for instance, and also in infections that bloom in the mouth and throat or bloodstream when the immune system breaks down.

But in that standard scenario, the yeast that has gone rogue only infects the person it was residing in. C. auris breaks that pattern. It has developed the ability to survive on cool external skin and cold inorganic surfaces, which allows it to linger on the hands of healthcare workers and on the doorknobs and counters and computer keys of a hospital room. With that assist, it can travel from its original host to new victims, passing from person to person in outbreaks that last for weeks or months.

Yeast is a fungus, but C. auris is behaving like a bacterium — in fact, like a bacterial superbug. It’s a cross-species shift as inexplicable as if a grass-munching cow hopped a fence and began bloodily chomping on the sheep in the pasture next door.

The accepted narrative of new diseases is that they always take us by surprise: Science recognizes it after it has begun to move, with the second patient or the tenth or the hundredth, and works its way back to find Patient Zero. But C. auris was flagged as troublesome from its first discovery, though its identifiers didn’t understand at the time what it might be able to do.

The accepted narrative of new diseases is that they always take us by surprise

The story begins in 2009, when a 70-year-old woman already in a hospital in Tokyo developed a stubborn, oozing ear infection. The infection didn’t respond when doctors administered antibiotics, which made them think the problem might be a fungus instead. A swab of her ear yielded a yeast that appeared to be a new species. Microbiologists Kazuo Satoh and Koichi Makimura named it for the Latin word for “ear.”

That story also would have ended in 2009—new species, new nomenclature, another entry in a textbook—except for an unnerving fact. Fungal infections have never been a high priority in medical research, and as a result, there are very few drugs approved for treating them—only three classes of several drugs each, compared to a dozen classes and hundreds of antibiotics for bacteria. This novel yeast was already showing some resistance to the first-choice antifungals that would have been used against it, a family of compounds called azoles that can be given by mouth.

The back-up choice, a drug called amphotericin, is IV-only, and also so toxic—its severe fever-and-chills reactions have been dubbed “shake and bake”—that doctors try to avoid it whenever possible. That left only one set of drugs available, a new IV-only class called echinocandins. C. auris entered medical awareness accompanied by the knowledge that, if it blew up into a problem, it would be difficult to treat.