First Molecularly Confirmed Outbreak of Bovine Pythiosis Caused by <em>Pythium insidiosum</em> in the Amazon Biome

Pythiosis is a neglected infectious disease caused by the aquatic oomycete Pythium insidi-osum and remains underrecognized in cattle, particularly in tropical regions. Here, we re-port the first molecularly confirmed outbreak of bovine pythiosis in the Amazon biome, affecting more than 400 animals raised under extensive production systems and areas with prolonged exposure to standing water. Clinically affected cattle presented ulcerative and exudative cutaneous lesions, predominantly involving the distal limbs. Given the di-agnostic challenges associated with pythiosis, etiological confirmation was achieved through quantitative PCR (qPCR) targeting the internal transcribed spacer (ITS) region of P. insidiosum, providing rapid and specific molecular detection during the outbreak inves-tigation. Therapeutic interventions were implemented as part of routine field management and included intramuscular triamcinolone combined with topical copper sulfate, which was associated with clinical improvement in a substantial proportion of affected animals, although treatment efficacy was not formally evaluated. The outbreak occurred in flood-prone pastures during the rainy season, highlighting the role of aquatic environ-ments in pathogen transmission. These findings expand current knowledge on bovine pythiosis in tropical ecosystems and emphasize the importance of molecular diagnostics, outbreak surveillance, and a One Health approach for the recognition and management of water-associated pathogens in livestock.