Massive outbreak of Influenza A H5N1 in elephant seals at Península Valdés, Argentina: increased evidence for mammal-to-mammal transmission

A massive outbreak of high pathogenicity avian influenza (HPAI) H5N1 in southern elephant seals at Península Valdés, Argentina, has provided unprecedented evidence for mammal-to-mammal transmission. The outbreak, which resulted in the death of approximately 17,000 individuals—disproportionately affecting seal pups—and disrupted social and breeding structures, was linked to frequent interactions with sea lions and scavenging by seagulls. Genomic characterization revealed that viruses from pinnipeds and terns in Argentina form a distinct clade with marine mammal viruses from Peru, Chile, and Brazil, sharing an identical set of mammalian adaptation mutations also found in the terns. This multinational transmission of H5N1 viruses in mammals is the first observed globally, suggesting increased evolutionary flexibility and potential global implications for wildlife, humans, and livestock.

Uhart, M., Vanstreels, R. E. T., Nelson, M. I., Olivera, V., Campagna, J., Zavattieri, V., Lemey, P., Campagna, C., Falabella, V., & Rimondi, A. (2024). Massive outbreak of Influenza A H5N1 in elephant seals at Península Valdés, Argentina: increased evidence for mammal-to-mammal transmission. https://doi.org/10.1101/2024.05.31.596774