Emerging human cases of sporotrichosis associated with feline outbreaks of Sporothrix brasiliensis in the Argentine Triple Frontier Region.

Sporotrichosis, caused by Sporothrix brasiliensis, is an emerging zoonotic mycosis that poses increasing risks in Latin America, particularly in underserved urban areas, with intensified human-animal-environmental interactions. Recently, Puerto Iguazú, Misiones, Argentina, a biodiversity hotspot in the Triple Frontier (Argentina, Brazil, and Paraguay), reported outbreaks suggestive of sustained feline sporotrichosis transmission. This prospective, observational study used passive surveillance, set in a One Health framework, to characterize the epidemiological features of feline sporotrichosis and associated zoonotic transmission to humans in Puerto Iguazú over a 21 month period, between August 2023 and April 2025. Domestic cats [cat(s); Felis catus], with suspected or confirmed sporotrichosis, and humans, with compatible cutaneous lesions and known contact with sick cats, were included. Laboratory confirmation involved culture, microscopy, and sequencing (ITS and CAL genes), with temporal and spatial analyses also performed. A combined total of 35 (44.9 %) of 78 cats from 57 households were classified as confirmed or probable sporotrichosis, with S. brasiliensis isolated from 26 (74.3 %) of these cases. Three asymptomatic cats tested positive for sporotrichosis via nasal swabs. Four human cases were identified, all with prior exposure to infected cats. Phylogenetic analysis confirmed all isolates clustered within the S. brasiliensis clade. A seven-month gap separated the first feline and human cases, with temporal analyses showing a progressive increase in feline cases, often preceding human infections in the same household. Spatial mapping identified a primary cluster in the northwestern urban core near the Iguazú River. This study documents the largest zoonotic sporotrichosis outbreak reported in Argentina to date and underscores the urgent need for integrated One Health surveillance, early detection, and inclusion of asymptomatic animals in control strategies.