A deadly fungus that can infect cats and people is spreading

It’s just a matter of time before it reaches the U.S., a CDC expert warns A fungus that first started infecting cats in Brazil is spreading through South America. Cats, like these two brawling in the street in Brazil, can spread the disease by scratching and biting or by grooming. Priscylla Barros/iStock/Getty Images Plus Listen to this article This is a human-written story voiced by AI. Got feedback? Take our survey . (See our AI policy here .) WASHINGTON — Microbiologists are used to looking at gross pictures and hearing scary statistics. So when a moderator of a session on emerging fungal infections at the ASM Microbe meeting uttered the words “somewhat terrifying,” it caught my attention. He was referring to a sexually transmitted skin infection that is becoming increasingly drug resistant. But what came next was even more horrifying to me. Medical mycologist Shawn Lockhart stepped to the podium and began describing a fungal disease that attacks cats, causing oozing skin ulcers and worse, and spreads to humans. It isn’t yet in the United States … that officials know of. But the disease, caused by Sporothrix brasiliensis, has sickened and killed thousands of cats and infected more than 11,000 people and at least 200 dogs in South America since its emergence in Brazil in the 1990s. Sign up for our newsletter We summarize the week s scientific breakthroughs every Thursday. “What we have right now is this ginormous ongoing outbreak of Sporothrix brasiliensis in Brazil,” Lockhart, a senior adviser at the U.S. Centers for Disease Control and Prevention, said June 7. 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 told me after the session. “We’re waiting.” He worries about the fungus spreading in big cities such as Istanbul and Bangkok where “cats are just everywhere,” and in rural areas in the United States where large populations of farm cats roam freely. “All it takes is one traveler [from South America] bringing their cat with them, and it can emerge anywhere,” Lockhart said during the presentation. “This is something we are very, very worried about.” Infected cats develop skin ulcers and nodules and swollen lymph glands. If the infection isn’t treated with antifungal drugs, it can become a respiratory disease 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, it causes painful skin ulcers. If untreated, the disease can also be severe and may kill those who have weakened immune systems. Risk of contagion is complicated because symptoms don’t always show up right away. Two members of a family who moved from Brazil to the United Kingdom developed the disease three years after the move, health authorities reported in 2022. One of the family’s two cats turns out to have been infected with Sporothrix brasiliensis. A vet who treated the cat was also infected. The fungi’s unusual properties may help it conquer new territory. The cat-infecting fungus is a relative of Sporothrix schenckii fungi that cause skin infections , called sporotrichosis or rose growers’ disease. Like many other soil-dwelling fungi, Sporothrix fungi are dimorphic, meaning they have two forms. “It is a mold in the cold and a yeast in the beast,” Lockhart said. That means it grows as long, stringy filaments known as hyphae in soil but then changes to single-celled yeast when its spores infect people or animals. 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 S. brasiliensis can spread in its yeast form, Lockhart said. “That doesn t happen with any of the other dimorphic fungi.” In soil, Sporothrix brasiliensis grows as long threads called hyphae (right) but in the body the fungus transforms into single-celled yeast (left) like these taken from a wound from an infected cat. Shown are yeast (oblong shapes with white outlines) in and among feline immune cells (larger cells). Usually spores from fungi are inhaled or enter through breaks in the skin, but the yeast form of S. brasiliensis is also contagious. A. Barros et al/Brazilian Journal of Veterinary Research, 2025A. Barros et al/Brazilian Journal of Veterinary Research, 2025 Cat behavior may be why felines seem more susceptible to catching S. brasiliensis, Lockhart said. “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. Those are their two most frequent activities, both of which allow the transfer of Sporothrix brasiliensis from one to another.” Cat scratches and bites may inject the yeast directly into other cats, people, dogs and other animals. “I m convinced that hal

A deadly fungus that can infect cats and people is spreading

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