Epidemiological data of an influenza A/H5N1 outbreak in elephant seals in Argentina indicates mammal-to-mammal transmission

H5N1 high pathogenicity avian influenza virus has killed thousands of marine mammals in South America since 2022. Here we report epidemiological data and full genome characterization of clade 2.3.4.4b H5N1 HPAI viruses associated with a massive outbreak in southern elephant seals (Mirounga leonina) at Península Valdés, Argentina, in October 2023. We also report on H5N1 viruses in concurrently dead terns. Our genomic analysis shows that viruses from pinnipeds and terns in Argentina form a distinct clade with marine mammal viruses from Peru, Chile, Brazil and Uruguay. Additionally, these marine mammal clade viruses share an identical set of mammalian adaptation mutations which were also present in tern viruses. Our combined ecological and phylogenetic data support mammal-to-mammal transmission and occasional mammal-to-bird spillover and suggest multinational transmission of H5N1 viruses in mammals. We reflect that H5N1 viruses becoming more evolutionary flexible and adapting to mammals in new ways could have global consequences for wildlife, humans, and/or livestock.

Instituto de Virología

Fil: Uhart, Marcela M. University of California Davis. School of Veterinary Medicine. Karen C. Drayer Wildlife Health Center; Estados Unidos

Fil: Uhart, Marcela M. Southern RightWhale Health Monitoring Program; Argentina

Fil: Vanstreels, Ralph E. T. University of California Davis. School of Veterinary Medicine. Karen C. Drayer Wildlife Health Center; Estados Unidos

Fil: Nelson, Martha I. National Institutes of Health. National Library of Medicine. National Center for Biotechnology Information; Estados Unidos

Fil: Olivera, Valeria Soledad. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Virología e Innovaciones Tecnológicas; Argentina

Fil: Olivera, Valeria Soledad. Consejo Nacional de Investigaciones Científcas y Técnicas; Argentina

Fil: Campagna, Julieta. Wildlife Conservation Society. Argentina Program; Argentina

Fil: Zavattieri, Victoria. Wildlife Conservation Society. Argentina Program; Argentina

Fil: Lemey, Philippe. Laboratory for Clinical and Epidemiological Virology. Rega Institute. Department of Microbiology, Immunology and Transplantation; Bélgica

Fil: Campagna, Claudio. Wildlife Conservation Society. Argentina Program; Argentina

Fil: Falabella, Valeria. Wildlife Conservation Society. Argentina Program; Argentina

Fil: Rimondi, Agustina. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Virología e Innovaciones Tecnológicas; Argentina

Fil: Rimondi, Agustina. Consejo Nacional de Investigaciones Científcas y Técnicas; Argentina

Fil: Rimondi, Agustina. Robert Koch Institute-Alexander von Humboldt fellowship; Alemania