H5N1 2.3.4.4b Clade Infection in Lactating Ferrets Leads to 100% Mortality

• The highly pathogenic avian influenza A (H5N1) virus of clade 2.3.4.4b has rapidly spread across Africa, Asia, and Europe.

• The virus first spread to North America and South America in 2021-2022, causing large-scale mortality of seabirds.

• The virus spread along the coast of Peru and Chile in 2022-2023, infecting and killing 30,000 sea lions, 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.

• The virus was first reported in cattle in Texas by the end of March 2021.

• As of November 22, 2024, 58 H5N1 cases in people have been reported in the U.S., and the virus has spread to 616 dairy herds across 15 States, with 402 herds in California alone.

• The study found that lactating ferrets with mammary gland infection with the H5N1 influenza virus (2.3.4.4b clade) are capable of spreading and causing disease in suckling ferret pups.

• Intramammary H5N1 virus infection resulted in 100% mortality of kits four days post-inoculation and six days post-inoculation in the case of the lactating ferrets.

• The presence of virus in the mammary gland suggests active viral replication within the gland.