Highly Pathogenic Avian Influenza Virus Subtype 5 in Cetaceans, Brazil

A research team identified highly pathogenic avian influenza virus subtype H5 in stranded dolphins along the coast of Brazil from November 2023 to August 2025. Samples were collected from three coastal regions: Rio Grande do Sul (approximately 485 km), Rio de Janeiro (317 km), and Ceará (573 km). Infected animals included species classified as vulnerable or endangered. The research highlights the need for continued surveillance of cetaceans susceptible to viral infections, which pose an additional threat to threatened species. Brazil is home to more than 46 cetacean species, several of which are classified as threatened or near threatened. Reported cases of influenza A virus in cetaceans remain rare and large-scale outbreaks have not been documented previously.