The emergence and spread of highly pathogenic avian influenza A (H5N1) in dairy cattle in the United States has been identified by scientists at the United States Department of Agriculture’s National Animal Disease Center, in collaboration with multiple academic, state, and federal partners.
Genetic analysis confirmed that a reassortment event in wild birds preceded a single transmission to cattle. Asymptomatic or presymptomatic cattle then facilitated the spread of the virus across the country. Viral genome sequencing revealed low-frequency mutations linked to transmission efficiency and mammalian adaptation, raising concerns about potential zoonotic spillover.
Highly pathogenic avian influenza viruses pose a significant threat to animal health, the agricultural economy, and potentially human health. The viruses related to the goose/Guangdong 2.3.4.4 hemagglutinin H5NX clade have spread to nearly 100 countries, leading to a recognized panzootic.
After the introduction of clade 2.3.4.4b H5N1 in late 2021, widespread outbreaks occurred in North America, causing extensive mortality among wild birds, poultry, and mammals. Cross-species transmission events raised concerns about the virus’s adaptation potential, highlighting the need for monitoring and understanding the risks for human infection and transmission.
In a recent study published in Science, researchers conducted a genomic and epidemiological investigation to determine the source, spread, and implications of the highly pathogenic avian influenza outbreak in dairy cattle. Samples were collected from dairy and poultry farms across multiple states, and whole-genome sequencing was performed on viral samples to trace the source and spread of the infection.
The study revealed that a wild bird-to-cattle spillover event in late 2023 led to the spread of the virus across multiple states. The virus persisted in cattle and was transmitted to poultry, raccoons, cats, and various wild bird species. Monitoring of cattle and other agricultural animals is crucial to assess the risk of zoonotic transmission and potential pandemic threats.
The findings underscore the importance of early detection, monitoring, and a National Milk Testing Strategy to prevent the spread of highly pathogenic avian influenza in dairy cattle and mitigate the risk of transmission to humans and other animal hosts. Further research and surveillance are needed to understand and address the evolving threat posed by these viruses.
