Deadly cat fungus inches toward U.S. after outbreaks

A drug-resistant fungal outbreak linked to Sporothrix brasiliensis—already sickening and killing thousands of cats and infecting more than 11,000 people in South America—has spread beyond Brazil to multiple neighboring countries. At a major microbiology meetin

In a conference hall in Washington. the kind of atmosphere where emerging threats are supposed to stay abstract. a remark landed like a hard knock: “somewhat terrifying.” The comment wasn’t about a new virus or a familiar bacterium. It was about a fungus—one that attacks cats. spreads to people. and is building resistance to drugs as it moves.

Medical mycologist Shawn Lockhart, a senior adviser at the U.S. Centers for Disease Control and Prevention. described Sporothrix brasiliensis as an outbreak already running out of control in Brazil and spilling across borders. It’s not yet in the United States. officials know of. he said—but the numbers behind his warning are grim. Since emerging in Brazil in the 1990s. the disease has sickened and killed thousands of cats and infected more than 11. 000 people. It has also infected at least 200 dogs.

Lockhart told the session on June 7 that what microbiologists are watching is “this ginormous ongoing outbreak of Sporothrix brasiliensis in Brazil.” He said the fungus has spread beyond Brazil to cats, dogs, and people in Paraguay, Chile, Argentina, and most recently Uruguay.

“It’s just a matter of time” until the fungus reaches the United States, Lockhart said after the session. “We’re waiting.”

The fear is not only that Sporothrix brasiliensis could arrive. It’s that it could take hold quickly—because of where cats live and how they behave.

Lockhart pointed to big cities such as Istanbul and Bangkok. where “cats are just everywhere.” He also described rural areas in the United States. where large populations of farm cats roam freely. In his account. the simplest pathway is travel: “All it takes is one traveler [from South America] bringing their cat with them. and it can emerge anywhere.”.

“ This is something we are very, very worried about,” he said during the presentation.

For cats, the infection can be brutal. Lockhart said Sporothrix brasiliensis causes oozing skin ulcers. Infected cats develop skin ulcers and nodules and swollen lymph glands. If the infection isn’t treated with antifungal drugs. the disease can become a respiratory illness and spread throughout the body.

“Without treatment, it’s 100 percent fatal, and even with treatment, it has a pretty high fatality rate,” Lockhart said.

In people, the fungus causes painful skin ulcers. Untreated disease can become severe and may kill people whose immune systems are weakened.

Adding to the danger is timing. Symptoms don’t always appear right away, which can hide new cases until the infection is already moving through a household or clinic.

The situation can stay quiet long enough for it to surprise public health systems. Health authorities reported in 2022 that two members of a family who moved from Brazil to the United Kingdom developed the disease three years after the move. One of the family’s two cats turned out to have been infected with Sporothrix brasiliensis. and the vet who treated the cat was also infected.

Even when symptoms are present, spotting the fungus is not straightforward. Lockhart said there’s no commercially available test for Sporothrix brasiliensis. and that cats coming into the United States just need a certificate from a vet saying they appear healthy. That creates a situation where the disease can be missed at the point of entry.

Lockhart also warned about a contradiction that would feel familiar to anyone who works in infectious disease: the fungus spreads in ways that don’t match the simplest model of infection.

Sporothrix brasiliensis is a relative of Sporothrix schenckii fungi that cause skin infections called sporotrichosis, or rose growers’ disease. Like other soil-dwelling Sporothrix fungi, it is dimorphic—meaning it has two forms. Lockhart described how it behaves: “It is a mold in the cold and a yeast in the beast.” In soil. the fungus grows as long. stringy filaments called hyphae. When spores infect people or animals, it changes to a single-celled yeast.

Most fungal infections happen when people inhale spores or, in the case of rose growers’ disease, when spores enter skin through scratches and puncture wounds from rose thorns. But Lockhart said Sporothrix brasiliensis can spread in its yeast form.

“That doesn’t happen with any of the other dimorphic fungi,” he said.

What makes cats central in this story is not just biology—it’s behavior.

Lockhart said cats are susceptible because of how they interact: “Those of you who have cats. you know they do two things: They’re loving all over each other. grooming each other. licking. or they’re fighting. biting and scratching.” He said both activities can transfer Sporothrix brasiliensis from one cat to another.

Cat scratches and bites can inject the yeast directly into other cats, people, dogs, and other animals. He added a startling detail that he believes is underrecognized in human cases: “I’m convinced that half of the human cases that come from cats are people who are trying to stuff pills down their cat’s throats to treat the sporotrichosis. ” getting scratched and bitten in the process. Grooming can also spread the fungus around a cat’s body or to other cats, he said.

There is another way cats may spread it, through air and surfaces. Researchers reported in Medical Mycology in 2022 that infected cats can sneeze out infectious yeast. Lockhart said. “When the cat’s sneezing. it’s going on the surface. it’s going on the lab coats. it’s going into the air. it’s going everywhere.”.

And even after an infected cat leaves a room, the fungus may not. Lockhart said laboratory testing suggests the fungi can live on surfaces for a long time—up to 10 weeks on stainless steel discs designed to mimic veterinary examination tables. In the same comparison, he said Candida albicans lasted 48 hours, while Candida auris died after about a month.

That persistence matters because it changes what “clean enough” means in veterinary settings. Lockhart said the fungus could infect other patients if veterinarians miss a spot while cleaning.

The good news, he said, is that the fungus is easy to kill with bleach and ethanol.

But good disinfectants won’t compensate for missed detection at the front end. Because there is no widely available test and healthy-looking cats can enter on a vet certificate, the first warning may depend on people who notice unusual cases early.

Lockhart urged pet health professionals to notify local public health labs or the CDC if they start seeing cases of sporotrichosis.

“There is an opportunity for it to spread quite easily,” he said. “We need veterinarians working with infection prevention and public health to make sure that this doesn’t get here and happen in the U.S.”

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