For the first time during the 2022 highly pathogenic avian influenza (HPAI) outbreak, a strain of the H5N4 serotype was found in the United States.

A backyard flock in Teton County, Montana, was confirmed to have been infected with HPAI on September 15, the United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) reported at the time.

However, a report released on October 20 by the World Organisation for Animal Health (WOAH) revealed that this case – involving approximately 2,610 birds – was of the H5N4 serotype.

Up to this point, all cases of HPAI in the United States and Canada during this outbreak have been of the H5N1 serotype.

Testing for the flock was conducted at the USDA National Veterinary Services Laboratory in Ames, Iowa, although WOAH stated that the N type had not been determined until October 17.

According to the WOAH report, this strain is of the Eurasian lineage goose/Guandong clade, and this lineage of the virus is a reassortment of the initial HPAI strain that first appeared in North America in Newfoundland and Labrador, Canada, in December 2021.

WOAH also reported that strains of the H5N4 serotype had not previously been detected in the United States even prior to 2022. The animal health organizations did not disclose whether this serotype would have consequences that differed from those of the H5N1 serotype.

Birds on the premises were depopulated and disposed of, with those procedures being completed on September 16, while cleaning and disinfection of the property was completed on September 19.


The farm operators initially reported the case to animal health authorities after they had observed lethargy, depression and increased mortalities among the birds.

Because this is a backyard flock, this case should not have an impact on international poultry trade, in accordance with WOAH standards.

To learn more about HPAI cases in commercial poultry flocks in the United States and Canada, see an interactive map on 

Read our ongoing coverage of the global avian influenza outbreak.

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