Study shows fatal spread of H5N1 virus from ferrets to suckling kits
The study demonstrates that H5N1 2.3.4.4b clade infection in lactating ferrets leads to mastitis-related disease and transmission to suckling pups, resulting in 100% mortality among the pups
During 2020, the highly pathogenic avian influenza A(H5N1) virus of clade 2.3.4.4b emerged and rapidly spread across many parts of Africa, Asia, and Europe. In 2021-2022, the 2.3.4.4b clade of H5N1 first spread to North America and then to South America where it caused large-scale mortality of seabirds. Except for causing episodic mortality of pinnipeds and cetaceans in Europe and North America, the virus had not spread to marine mammals. But that changed when the virus spread along the coast of Peru and Chile in 2022-2023 infecting and killing 30,000 sea lions; the virus also spread to dolphins, otters, and other marine mammals.

In Argentina, the virus spread to and killed over 17,000 elephant seals, including almost 97% of the pups. Till the outbreak in different mammals, H5N1 viruses were considered to rarely infect mammals and not likely to spread among mammals.