Mississippi Poultry Flock Tests Positive for H7N9 in First Outbreak Since 2017

A broiler chicken breeder flock in Mississippi has tested positive for highly pathogenic avian influenza (HPAI) H7N9, according to the U.S. Department of Agriculture’s (USDA) Animal & Plant Health Inspection Service (APHIS).

APHIS previously documented H7 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 U.S. since 2017. 

This H7N9 virus is a fully North American (AM) virus of wild bird origin and is unrelated to the H5N1 virus currently circulating in the United States, said APHIS.

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. Spillovers of avian influenza from wild bird sources can occur due to breaches in biosecurity. APHIS closely monitors these subtypes because H5 and H7 LPAI viruses in poultry species such as chickens and turkeys can mutate into HPAI.

The flock of roughly 46,000 birds 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 at APHIS’ National Veterinary Services Laboratories (NVSL).

As part of existing avian influenza response plans, federal and state partners are working jointly on additional surveillance and testing in areas around the affected flock. USDA will report these findings to the World Organization for Animal Health (WOAH) as well as international trading partners.

According to the U.S. Centers for Disease Control and Prevention (CDC), the public health risk associated with these avian influenza detections in birds remains low.

Visit APHIS’ Defend the Flock Resource Center for additional materials about biosecurity, including videos, checklists and a toolkit.