Hidden threat: The evolving fungus that spreads through cats and humans

A study led by Dr. Anderson Messias Rodrigues (Federal University of São Paulo, Brazil), funded by the São Paulo Research Foundation (FAPESP), has uncovered new insights into the ongoing sporotrichosis epidemic in Brazil, the largest and most persistent outbreak of this fungal infection globally. The study is published in Mycology: An International Journal on Fungal Biology.

Sporotrichosis, a chronic infection affecting the skin and lymphatic system (and sometimes internal organs), is typically caused by Sporothrix fungi. Unlike most fungal infections, sporotrichosis can be transmitted zoonotically, with infected cats being a primary source of human infection through scratches, bites, or contact with secretions.

The research team analysed 104 Sporothrix isolates, focusing on the 3-carboxymuconate cyclase (CMC) gene, which encodes a major antigen called Gp60-70. They identified 79 unique variants, indicating greater genetic diversity than previously recognized. Molecular analysis revealed high polymorphism in Sporothrix brasiliensis and Sporothrix schenckii, suggesting recent population expansion or positive selection.

READ MORE: Exeter launches second round of global funding to tackle antifungal drug resistance

READ MORE: Farm gates and facial fungi: Tanu charts her journey towards commercialisation

Researchers have proposed that harmful environmental aromatic pollutants, which are common in urban areas (e.g., benzene, toluene, and polycyclic aromatic hydrocarbons), may act as selective pressures, favoring Sporothrix strains with increased CMC activity. Given that the CMC enzyme plays a role in the degradation of aromatic compounds via the β-ketoadipate pathway, this could provide an ecological advantage in polluted environments.

New molecular perspective

The study also predicted key B-cell epitopes and conserved glycosylation sites—potential targets for diagnostics, vaccines, and antifungal therapies. The presence of high-frequency derived alleles in S. brasiliensis suggests rapid adaptation, potentially leading to increased virulence. Furthermore, the CMC gene has proven to be a more effective molecular marker than traditional markers, offering improved resolution for differentiating strains and enhancing epidemiological surveillance.

Sporothrix brasiliensis, the most virulent Sporothrix species, is a key driver of the Brazilian epidemic. Compared with other species, it presents greater pathogenicity, transmission efficiency, and antifungal resistance. The outbreak, which originated in Rio de Janeiro in the late 1990s, has spread nationwide and to neighboring countries, fueled by high cat populations, socioeconomic challenges, and gaps in disease surveillance. Cat-to-cat and cat-to-human transmission are significant contributors to the rapid spread of S. brasiliensis.

“These findings offer a new molecular perspective on Sporothrix evolution and virulence,” says Dr. Rodrigues. “Understanding these fungal adaptations is crucial for developing better tools to diagnose, monitor, and control the spread of sporotrichosis among humans and cats.”

This study underscores the urgent need for enhanced fungal surveillance, particularly in areas experiencing an increase in cat-transmitted sporotrichosis. Identifying genetic markers linked to virulence could lead to new control strategies in both human and veterinary medicine, helping to address this growing public health crisis.