H5N1 adapts alarming to mammals in South America’s South Cone

In a concerning development for global public health and wildlife conservation, the highly pathogenic avian influenza virus H5N1 has shown increasing signs of adaptation to mammalian hosts in the Southern Cone of South America.

David Corredor

In a concerning development for global public health and wildlife conservation, the highly pathogenic avian influenza virus H5N1 has shown increasing signs of adaptation to mammalian hosts in the Southern Cone of South America. Recent outbreaks and scientific studies have revealed that the virus, traditionally confined to avian species, is now infecting and spreading among marine mammals, raising fears of a potential zoonotic leap to humans.

A 2023 outbreak in Argentina marked a turning point. Researchers from the University of California, Davis, and Argentina’s National Institute of Agricultural Technology (INTA) documented mass mortality among elephant seals along the Patagonian coast. Genetic analysis confirmed that the virus had not only infected these mammals but was also transmitting between them—an unprecedented event in the region.

The virus, belonging to clade 2.3.4.4b, has been evolving rapidly since its global resurgence in 2020. After devastating seabird populations in Europe and Africa, it reached the Americas in 2022. By early 2023, it had spread to Argentina, initially affecting poultry before jumping to marine mammals such as sea lions and elephant seals.

The Pan American Health Organization (PAHO) has confirmed outbreaks of H5N1 in mammals across several South American countries, including Argentina, Chile, and Peru. In Argentina’s Chubut province, a South American sea lion tested positive for the virus in 2024, highlighting its continued presence and potential for further adaptation.