Unique Genetic Clades and Frequent Zoonotic Transmission of Sporothrix brasiliensis with Reduced Itraconazole Susceptibility

Abstract

Sporothrix brasiliensis is driving a major zoonotic epidemic in Brazil, predominantly via cat-to-human transmission. In the late 1990s major outbreaks were reported in Rio de Janeiro (RJ) and Rio Grande do Sul (RS), the southernmost state. We characterized the antifungal susceptibility and genetic diversity of 450 S. brasiliensis isolates collected between 2009 and 2024 in RS to better understand treatment response, emergence and transmission. A bimodal distribution of the itraconazole minimum inhibitory concentration (MIC) was observed with 24% non-wild-type (NWT) isolates. Short tandem repeat genotyping revealed three main clades: One associated with RJ strains (Clade I) and two novel clades (Clades II and III). Clade II formed large transmission clusters with < 20% of isolates being NWT for itraconazole, similar to Clade I. Clade III demonstrated less clustering, higher genetic variation and NWT MICs for 89% of isolates. Finally, all NWT strains in human patients with cat-transmitted disease and available clinical data, appeared isolated prior to azole exposure. We report the emergence of genetically distinct S. brasiliensis clades in RS with different rates of reduced itraconazole susceptibility and evidence of zoonotic transmission of NWT isolates. Our findings highlight the urgent need for antifungal stewardship and surveillance in these endemic regions.