Deadly H5N1 Virus Spread: Ferrets to Suckling Kits Transmission Uncovered in New Study

During 2020, a highly pathogenic avian influenza virus, A(H5N1) of clade 2.3.4.4b, appeared and spread rapidly in Africa, Asia, and Europe. In 2021-2022, the virus reached North and South America, causing severe deaths among seabirds. It had typically caused occasional mortality in marine mammals, but this changed in 2022-2023 when it infected around 30,000 sea lions along the coasts of Peru and Chile, as well as dolphins and otters. In Argentina, over 17,000 elephant seals succumbed to the virus, with almost 97% of the pups affected.

By March 2023, the H5N1 virus was detected in cattle in Texas, and a farm worker tested positive on April 1 after exposure to infected dairy cattle. As of November 22, 2024, the U.S. reported 58 human cases and the virus spread to 616 dairy herds across 15 states, mainly in California.

The H5N1 virus primarily resides in the mammary glands of cows, with infected milk containing high levels of viral RNA. This raises concerns about breastfeeding as a potential way to transmit the virus to young animals and humans. To study this, researchers used ferrets, where lactating ferrets with H5N1 infections were able to transmit the virus to their pups, leading to high fatality rates in both.

A study published in Nature on October 28 highlighted that infected ferrets faced severe disease and 100% mortality. The virus spread effectively among directly contacted ferrets but did not transmit well through respiratory droplets. Ferrets inoculated with the virus showed a marked increase in viral RNA in their milk, suggesting active viral replication.

The study reported significant viral RNA levels in the oral cavity of the suckling kits, indicating that the virus could be transmitted through milk. While lactating ferrets showed no viral RNA in nasal secretions initially, close contact with the kits led to higher RNA levels in the mothers.

These findings show that H5N1 infections in lactating ferrets are more severe than H1N1 infections. The presence of the virus in mammary glands raises questions about public health and food safety, particularly concerning milk as a transmission vector.