A fungus called Sporothrix brasiliensis has been spreading through South America for three decades, sickening and killing thousands of cats and infecting more than 11,000 people. At the ASM Microbe meeting in Washington on June 7, CDC senior adviser Shawn Lockhart delivered a stark warning: it is not a matter of if, but when, it reaches the United States.
“It’s just a matter of time,” Lockhart told Science News after his presentation. “We’re waiting.”
S. brasiliensis is a dimorphic fungus, “a mold in the cold and a yeast in the beast,” as mycologists describe it. Unlike most disease-causing fungi, which grow as molds in the environment and only convert to yeast inside a host, S. brasiliensis can spread in its yeast form between animals and from animals to people.
The fungus emerged in Brazil in the 1990s and has since spread to Paraguay, Chile, Argentina, and most recently Uruguay. It is now considered a hyperendemic threat across large parts of South America. The World Health Organization reports that in some affected areas, sporotrichosis incidence reaches between 25 and 100 cases per 100,000 people.
How it spreads
The primary mode of transmission is through cat scratches and bites. Infected cats develop oozing skin ulcers and nodules, lesions teeming with yeast. When a cat scratches or bites, it injects the fungus directly into the wound.
But that is not the only route. Researchers have found that cats can sneeze out infectious yeast, and the fungus has been isolated from nasal cavities and respiratory droplets. It can survive for up to 10 weeks on stainless steel surfaces such as veterinary exam tables, far longer than Candida albicans (48 hours) or Candida auris (about one month). It is easily killed with bleach and ethanol, but its environmental persistence makes infection control in veterinary settings challenging.
Half of human cases may come from people who try to medicate their infected cats and get scratched or bitten in the process.
Why the CDC is worried
Only a single infected traveller bringing their cat into the country could establish the fungus in the United States. The incubation period can be long, two family members who moved from Brazil to the United Kingdom developed the disease three years after relocating. Their cat was infected, and a veterinarian who treated the cat also became infected.
There is no commercially available test for S. brasiliensis specifically, and cats entering the United States only need a veterinary certificate stating they appear healthy, easy to miss in an animal carrying a latent infection.
“It is a constantly evolving and spreading outbreak,” Lockhart said. “All it takes is one traveler from South America bringing their cat with them, and it can emerge anywhere.”
The disease
In cats, the infection begins as skin ulcers and swollen lymph nodes. Without treatment, it becomes respiratory, spreads systemically, and is 100% fatal. Even with antifungal treatment, itraconazole or terbinafine, the fatality rate remains high.
In humans, the disease typically causes painful skin ulcers at the site of inoculation. In immunocompromised individuals, people living with HIV, transplant recipients, and others, the infection can become invasive, causing arthritis, respiratory disease, and meningitis. A 2025 study in the CDC’s Emerging Infectious Diseases documented treatment failure even without initial drug resistance, especially in cats with severe disease.
Lockhart urged veterinarians in the United States to notify local public health labs or the CDC immediately if they encounter sporotrichosis cases. “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.”
Source: Science News, “A deadly fungus that can infect cats and people is spreading” by Tina Hesman Saey (June 19, 2026). https://www.sciencenews.org/article/deadly-fungus-cats-people-spreading