Cat-Linked Fungus Spreads in South America: Sporothrix brasiliensis Alert in Uruguay

A Fungal Infection Spreading from Cats to People: What to Know

A fungus, Sporothrix brasiliensis, is gaining a foothold in South America, with recent confirmation of cases in Uruguay linked to infections in cats, pets and people. This marks a shift in how this fungal infection is spreading, moving beyond traditional sources like soil and plants to a more direct link with feline populations. While the infection is treatable, understanding the transmission routes and recognizing early symptoms is crucial, especially for those with weakened immune systems or who frequently interact with cats.

How Cats Amplify the Spread

Sporothrix brasiliensis causes sporotrichosis, a skin infection that enters the body through breaks in the skin. What makes this particular fungus concerning is how efficiently cats transmit it. Open sores on infected cats, particularly around the nose, face, mouth, and paws, contain large numbers of fungal cells. Scratches, bites, or even contact with fluid from these wounds can easily introduce the fungus into human tissue. A recent review highlights that cats can transfer substantial amounts of the fungus through these interactions.

From Gardener’s Disease to Urban Zoonosis

Historically, sporotrichosis was often referred to as “gardener’s disease,” contracted through contact with soil, plants, or decaying organic matter. However, since the 1990s, researchers in Brazil identified Sporothrix brasiliensis, and the cat—particularly stray cats—became the primary source of infection. This shift is significant due to the fact that it means the fungus is now circulating more readily in urban environments. Before this recent alert in Uruguay, the country primarily saw cases linked to armadillo scratches during hunting, with a Udelar review documenting 157 cases over 38 years primarily from this source.

Recognizing the Symptoms in People and Pets

In people, sporotrichosis typically begins as a compact, red bump that can open and form an ulcer. More bumps may appear along lymphatic channels as the fungus spreads. In cats, symptoms often include persistent wounds, crusts, and hair loss, especially on the face and head. Red, draining eyes can also be a sign. It’s important to note that these symptoms can sometimes be mistaken for bacterial infections, leading to ineffective antibiotic treatment.

How Doctors Confirm the Infection

Diagnosis involves examining samples from sores under a microscope or culturing the fungus in a lab. Elisa Cabeza, from Universidad de la República (Udelar), emphasizes that early diagnosis is key, as the infection is curable with antifungal medications, though treatment can last for weeks or months. Managing the infection in cats, however, presents a greater challenge.

Who is Most Vulnerable?

While anyone can contract sporotrichosis, certain groups are at higher risk of severe illness. Young children, older adults, and individuals with compromised immune systems are particularly vulnerable. Rarely, the infection can spread beyond the skin to affect joints, lungs, or even the brain’s lining, making prompt diagnosis and treatment even more critical. Udelar investigators have specifically noted that children under two and older adults may experience more severe outcomes.

A Body-Heat Driven Transformation

The fungus exhibits a unique characteristic called dimorphism. Outside the body, it grows as branching threads, but when it enters a warm-blooded host, it transforms into a compact yeast form. This smaller form more easily penetrates damaged skin and multiplies within tissues, contributing to its ability to establish an infection. This adaptability helps the fungus survive both indoors and outdoors.

The Spread Beyond Uruguay

The situation isn’t limited to Uruguay. A 2024 report in Argentina linked two human cases to contact with sick cats, and the World Health Organization (WHO) reports more than 11,000 human cases in South America over the past decade. The movement of cats, both legal and informal, across borders is a significant factor in the fungus’s spread, as a single infected animal can introduce the fungus to new areas.

Challenges in Control and What Comes Next

Controlling the spread is complicated by the prevalence of stray cats, many of whom proceed undiagnosed and untreated. Research has even detected the fungus in droplets expelled when infected cats sneeze, expanding the potential routes of transmission beyond scratches and bites. Effective control requires a coordinated approach involving animal care, medical care, and community reporting.

The detection of Sporothrix brasiliensis in Uruguay signals a broader expansion of this fungal threat across southern South America. Rapid diagnosis, treatment for both people and pets, and improved management of stray cat populations will be essential to contain the outbreak and prevent further spread. Public health teams are now focused on strengthening surveillance, improving diagnostic capabilities, and educating the public about the risks and prevention measures.