The Mississippi Board of Animal Health (MBAH) has been notified by the U.S. Department of Agriculture’s National Veterinary Services Laboratory that poultry from a commercial broiler breeder chicken flock in Noxubee County tested positive for H7N9 highly pathogenic avian influenza (HPAI).
The USDA Animal and Plant Health Inspection Service (APHIS) has previously documented H7N9 low pathogenicity avian influenza (LPAI) in U.S. wild bird surveillance this year and in previous years, but this is the first HPAI H7 case in commercial poultry in the United States since 2017.
This H7N9 virus is a fully North American (AM) virus of wild bird-origin and is unrelated to the Eurasian H5N1 clade 2.3.4.4b virus currently circulating in the United States. Some AM H7 LPAI viruses detected as part of APHIS’ wild bird surveillance are closely related to this HPAI virus, indicating a recent spillover of wild bird-origin LPAI virus. The flock was experiencing high mortality, and samples tested at the Mississippi Veterinary Research & Diagnostic Laboratory, a member of the National Animal Health Laboratory Network, were presumptive positive for HPAI then confirmed as H7N9 at the APHIS National Veterinary Services Laboratories (NVSL). The state veterinarian quarantined the premises, and the MBAH coordinated a joint incident response with federal animal health officials in Mississippi. The birds on the property were depopulated to prevent the spread of the disease. Birds did not enter the food system.
The MBAH is actively working with federal partners and the poultry industry to increase monitoring of flocks statewide. This finding is the third case of highly pathogenic avian influenza (HPAI) in commercial poultry in Mississippi since the spring of 2023. Since November 2024, HPAI has been detected in migratory waterfowl in multiple areas of Mississippi.