
On November 23, 2024, two HPAI viruses were identified in samples from a farm rearing meat ducks in Merced County in California.
Increased mortality was observed at the premises, leading the state veterinary authority to quarantine the farm.
According to the recently submitted official notification to the World Organisation for Animal Health (WOAH), depopulation of all 118,945 birds was completed in early December.
As well as the now-familiar HPAI H5N1 clade 2.3.4.4b Eurasian lineage-goose/Guangdong virus, a second virus serotype was detected at the farm.
This was an H5N9 virus belonging to the same clade, and it is the first time this virus serotype has been detected in the U.S.
No particular concerns about this development are raised in the WOAH report.
In response to HPAI-related events, the USDA Animal and Plant Health Inspection Service and state animal health officials continue to conduct epidemiological investigations and enhanced surveillance.
Previous detection of H5N9 HPAI virus
An H5N9 virus has been isolated at a live bird market in China, according to a research paper published in the Journal of Virology in 2015.
In that case, the origin of the hemagglutinin (H) gene in the H5N9 virus was an H5N1 virus from a duck in Vietnam, and belonged to clade 2.3.2.1. The neuraminidase (N) gene originated in an H7N9 virus previously isolated in China, according to the researchers.
The virus isolated from the Californian farm in 2024 appears to have different origins from the one from the Chinese study, and will likely have other characteristics.
View our continuing coverage of the global avian influenza situation.
To learn more about HPAI cases in commercial poultry flocks in the United States, Mexico and Canada, see an interactive map on WATTPoultry.com.