ATTN Catsby: A fungus that spreads from cats to humans has been detected, raising concerns among scientists
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Researchers have confirmed the arrival of Sporothrix brasiliensis in Uruguay, marking a new stage in the spread of a fungal infection increasingly linked to cats across South America. The organism causes Sporotrichosis, a skin infection that can affect both humans and animals.
The discovery followed investigations into infections among people, pets, and local animals along Uruguay’s southeastern coast. What initially appeared to be a single isolated case has now become evidence that the fungus may be spreading locally.
Cats and the emerging fungal threat
Health authorities began investigating after reports of unusual skin infections appeared in the departments of Maldonado and Rocha. A notice from Uruguay’s Institute of Hygiene documented infections in cats, other pets, and humans.
Research led by Elisa Cabeza from Universidad de la República connected those cases to Sporothrix brasiliensis.
Cabeza’s team later found infected cats in multiple locations without any link to the originally suspected kitten, suggesting the fungus was already circulating in local animal populations.
This shifted the situation from a single household problem to a broader public health concern.
Why cats spread the fungus so efficiently
Cats are particularly effective at transmitting this fungal species. Open sores on infected animals often contain large numbers of fungal cells, especially around the nose, mouth, face, and paws.
When a cat scratches or bites someone, the fungus can enter directly through broken skin. Even contact with fluid from infected wounds can transmit the organism.
Studies have shown that infected cats can transfer large quantities of yeast-like fungal cells during scratches, bites, and contact with wound secretions.
Because many stray cats roam widely, fight with other animals, and move between neighborhoods, they can spread the infection before authorities detect an outbreak.
A fungus that changes with temperature
One feature that helps the organism survive is its ability to change form depending on temperature.
Outside a host, Sporothrix brasiliensis grows as thin branching filaments. But when exposed to body heat inside mammals, it transforms into a compact yeast-like form.
Scientists call this process dimorphism, a temperature-driven switch between two growth forms.
The smaller yeast cells can settle into damaged skin more easily and multiply within living tissue. This adaptability helps the fungus persist both in the environment and inside animal hosts.
Symptoms of sporotrichosis in people
In humans, sporotrichosis typically begins with a small red bump at the site of a scratch or injury.
Over time, the bump may break open into a sore. Additional nodules can then appear in a line along nearby lymphatic channels under the skin.
Most infections remain limited to the skin and lymph system. However, in rare cases the fungus can spread to joints, lungs, or the lining of the brain.
Young children, older adults, and people with weakened immune systems are more likely to experience severe illness.
How the disease appears in cats
Cats infected with Sporothrix brasiliensis often develop stubborn wounds that do not heal easily.
Common signs include:
- crusted sores and hair loss
- open wounds on the face or head
- swollen or draining lesions
- inflamed or infected eyes
Because these wounds contain large amounts of fungus, infected cats are considered the main drivers of transmission.
Confirming the infection
Doctors confirm sporotrichosis by examining material taken from a skin lesion under a microscope or by growing the fungus in laboratory culture.
The infection is treatable with antifungal medication, though treatment can last several weeks or months.
Misdiagnosis is common because the sores resemble bacterial infections. Patients may initially receive antibiotics, which are ineffective against fungal diseases.
A regional outbreak already underway
Across South America, Sporothrix brasiliensis has caused thousands of infections linked to cats.
According to the World Health Organization, more than 11,000 human cases have been reported in the region over the past decade. Brazil has experienced the largest outbreaks, with cases spreading into neighboring countries.
Reports from Argentina in 2024 linked two human infections to contact with sick cats, highlighting how easily the disease can cross borders.
Uruguay’s changing pattern of infection
Historically, sporotrichosis in Uruguay was associated mainly with environmental exposure rather than animals.
A long-term review identified 157 cases over nearly four decades. Most were linked to armadillo scratches during hunting.
The recent emergence of cat-linked infections therefore represents a new and more difficult pathway for the disease to spread.
Challenges for public health
Controlling outbreaks becomes much harder when stray cats are involved. Many infected animals are never diagnosed or treated, allowing them to continue spreading the fungus.
Some studies have even detected the fungus in droplets expelled when infected cats sneeze, raising additional concerns about transmission.
Health officials say effective control requires cooperation between veterinarians, doctors, and local communities.
Without coordinated action, untreated animals can keep the infection circulating long after human cases appear.
What the discovery means
The detection of Sporothrix brasiliensis in Uruguay shows that a fungus once largely associated with Brazilian outbreaks is gaining new footholds across southern South America.
Experts say rapid diagnosis, treatment for both people and pets, and better management of stray cat populations will determine whether the spread can be contained.
The findings were published in the journal Medical Mycology Case Reports.
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