They're circulating more widely than we'd imagined
A pathogen long associated with domestic cats has now been found quietly residing in the hearts and livers of wild mammals, birds, and reptiles along Brazilian highways, suggesting that nature harbors reservoirs of disease far broader than medicine has assumed. Researchers in Paraná, working across six years and hundreds of kilometers of roadside carcasses, detected three species of Sporothrix fungus in eleven wild animals — including birds, whose high body temperatures were thought to make them immune. The discovery does not yet tell us how sick these animals were, but it tells us something older and more unsettling: that the boundaries we draw between wild, rural, and human worlds are thinner than we imagine, and that what circulates silently in one domain may not stay there.
- A fungus capable of causing disfiguring skin lesions in humans has been found living inside the internal organs of wild animals across Brazil, upending assumptions about where this pathogen actually lives.
- The detection of Sporothrix in birds — creatures whose 42°C body temperature was believed to be a natural firewall against fungal infection — forces a fundamental revision of how scientists understand this pathogen's resilience.
- Eleven of 81 roadkill animals tested positive across highways cutting through Atlantic Forest, grasslands, and farmland, with heart and liver tissue most frequently infected, raising the possibility of widespread asymptomatic carriers in the wild.
- Transition zones where forests, farms, and cities blur are showing the highest concentrations of infected animals — precisely the spaces where wild and human lives most frequently collide.
- Researchers warn that habitat fragmentation is not just an ecological crisis but an epidemiological one, as shrinking wild spaces push potential reservoirs of disease into closer contact with domestic animals and people.
A fungus long known to spread through domestic cat scratches and cause serious skin lesions has now been found living inside wild animals across Brazil — in their hearts, livers, and other internal organs. The discovery, published in Mycopathologia, suggests that wildlife may be quietly harboring a pathogen capable of infecting humans, and raises urgent questions about how widely it is actually circulating in nature.
Researchers from the State University of Londrina spent six years collecting carcasses of animals struck by vehicles along two highways in Paraná, gathering tissue samples from 81 animals — mammals, birds, and reptiles — that had died across 680 kilometers of road cutting through Atlantic Forest, native grasslands, and farmland. The project was designed to use roadkill as sentinels for emerging diseases threatening human health.
Analysis of 178 tissue samples revealed genetic material from three Sporothrix species in 11 animals. The heart and liver were most frequently infected. The most common species, S. schenckii, appeared in seven animals; S. brasiliensis turned up in two birds; and S. globosa — the rarest in Brazil — was found in an agouti, several birds, and a false coral snake. Two animals carried two fungal species simultaneously. Among those infected was the southern tigrina, an endangered small wild cat, underscoring that the fungus is not confined to a narrow set of hosts.
Perhaps most surprising was the presence of the fungus in birds. Conventional understanding holds that birds are naturally protected from pathogenic fungi because their body temperature reaches 42°C — a heat that should kill most fungal threats. Yet pathogenic Sporothrix survived and circulated in birds regardless.
Study coordinator Anderson Messias Rodrigues noted that the team could not confirm whether the fungi were actively causing disease, but the presence of fungal DNA in anatomically intact internal organs suggested the animals were either infected or asymptomatic carriers. The geographic pattern deepened concern: infected animals clustered in transition zones where forests, farmland, and urban areas overlap — the very places where wild animals, domestic animals, and humans are most likely to meet.
For humans, sporotrichosis typically begins at a scratch or puncture wound and, if untreated, can spread along the lymphatic system in a chain of lesions. As habitat loss pushes wildlife closer to human settlements, the risk of exposure may be considerably greater than previously understood.
A fungus that has long been known to spread among domestic cats and cause serious skin lesions has now been found living inside wild animals across Brazil—in their hearts, livers, and other internal organs. The discovery, published in March in the journal Mycopathologia, suggests that wildlife may be quietly serving as reservoirs for a pathogen that can infect humans, and raises questions about how widely this fungus is actually circulating in nature.
Researchers collected carcasses of animals struck by vehicles along two highways in the Brazilian state of Paraná between 2017 and 2023. Over six years, they gathered tissue samples from 81 animals—39 mammals, 36 birds, and six reptiles—that had died along 530 kilometers of BR-376, which runs through Atlantic Forest areas, and 150 kilometers of PR-445, which borders native grasslands and farmland. The work was part of a larger effort by the Department of Preventive Veterinary Medicine at the State University of Londrina to use wild animals as sentinels for emerging diseases that might threaten human health.
When researchers analyzed 178 tissue samples from the hearts, livers, lungs, and bladders of these animals, they found genetic material from three species of Sporothrix fungus in 11 of them. The heart and liver were the organs most frequently infected, appearing in six and five animals respectively. The most common species was S. schenckii, detected in eight samples from seven animals. S. brasiliensis, which causes most sporotrichosis cases in Brazil, turned up in only two birds. S. globosa, the rarest species in the country, was found in an agouti, several birds, and a false coral snake. In two cases, individual animals carried two fungal species at once.
The range of animals infected was striking. The fungus appeared in mammals, birds, and at least one reptile—including an endangered species, the southern tigrina, a small wild cat. This last finding was particularly significant because it suggested the fungus was not confined to a narrow set of hosts. What made the discovery even more unexpected was its presence in birds. Conventional thinking holds that birds are naturally protected from pathogenic fungi because their body temperature reaches 42 degrees Celsius, roughly 108 degrees Fahrenheit, a heat that should kill most fungal pathogens. Yet here was clear evidence that pathogenic Sporothrix species could survive and circulate in birds despite that high internal temperature.
Anderson Messias Rodrigues, a professor at the São Paulo School of Medicine of the Federal University of São Paulo and coordinator of the study, emphasized that the team could not determine whether the fungi were actively causing disease in these wild animals. The presence of fungal DNA in internal tissues—particularly in organs like the heart and liver that were anatomically intact and unexposed to environmental contamination—suggested the animals were either infected or serving as asymptomatic carriers. "It's clear that they're circulating more widely than we'd imagined, posing a potential risk to human and animal health," Rodrigues said.
The geographic pattern of the findings added another layer of concern. Transition zones where native forests, rural farmland, and urban areas overlapped showed higher concentrations of infected animals. These are precisely the places where wild animals and domestic animals—and by extension, humans—are most likely to come into contact. As human development continues to fragment and encroach on natural habitats, the boundaries between wild, rural, and urban spaces are becoming increasingly blurred. "We're witnessing the emergence of Sporothrix in new hosts," Rodrigues noted. "The study opens the door to new research by showing that the reservoirs of the fungus extend far beyond domestic animals."
For humans, sporotrichosis typically begins as a skin infection at the site of a scratch or puncture wound, often from a cat. Left untreated, the infection can spread along the lymphatic system, causing a chain of lesions that move up the arm or leg. In domestic animals, the disease causes serious tissue damage. The discovery that wild animals may be harboring and potentially transmitting these fungi suggests that the risk of human exposure may be greater than previously understood, particularly in regions where habitat loss is pushing wildlife closer to human settlements.
Citações Notáveis
They're circulating more widely than we'd imagined, posing a potential risk to human and animal health.— Anderson Messias Rodrigues, coordinator of the study
We're witnessing the emergence of Sporothrix in new hosts. Human pressure on the environment is blurring the boundaries between what's rural, urban and wild.— Anderson Messias Rodrigues
A Conversa do Hearth Outra perspectiva sobre a história
So these fungi were found in wild animals' organs—does that mean the animals were sick?
Not necessarily. The researchers found the fungal DNA, which proves it was there, but they couldn't confirm whether it was actively causing disease. The animals might have been asymptomatic carriers, or the infection might have been dormant. That's actually one of the unsettling parts—we don't know if these animals are just living with the fungus or if they're spreading it.
Why does it matter that it was in the heart and liver specifically?
Those are internal organs that weren't exposed to the environment after the animals died, so contamination from outside sources is unlikely. Finding the fungus there suggests it was genuinely circulating through the animal's body, not just on the surface. It's a sign of systemic presence.
The article mentions birds shouldn't be able to host this fungus because of their body temperature. What changed?
That's the assumption that got overturned. Birds maintain temperatures around 42 degrees Celsius, which scientists thought would kill pathogenic fungi. But this study found the fungus thriving in birds anyway. It means the fungus is more adaptable than we gave it credit for.
What's the connection between habitat loss and this discovery?
The researchers found more infected animals in transition zones—places where forest, farmland, and towns blur together. As humans develop land and push into wild areas, animals that normally wouldn't encounter each other are now sharing space. That's how a fungus that spreads among domestic cats ends up in wild mammals, birds, and reptiles.
Can humans catch this from wild animals?
That's the open question now. We know humans can get sporotrichosis from cats. We now know wild animals carry the fungus. The risk exists, especially in areas where people and wildlife overlap. But the study doesn't tell us how often that transmission actually happens.
What happens next?
More research. The team couldn't do certain tests on these samples that might have shown whether the infections were active. Future studies will likely dig deeper into how the fungus moves between species, whether wild animals are truly reservoirs, and what the actual risk to humans is in different regions.