HPAI, sometimes introduced by wild birds, can quickly spread through poultry flocks.
HPAI, sometimes introduced by wild birds, can quickly spread through poultry flocks.

Earlier this week, the USDA confirmed an outbreak of highly pathogenic avian influenza (HPAI) in a chicken breeder flock in Lincoln County, Tennessee. Now the agency’s National Veterinary Services Laboratories (NVSL) has identified the virus subtype as H7N9, although the virus is genetically distinct from the China H7N9 subtype that emerged in 2013.

This is the first known HPAI outbreak in U.S. poultry this year. Animal-health officials currently are de-populating the affected flock of 73,500 birds while also conducting an epidemiological investigation and a surveillance and testing program within a 10-mile radius of the affected farm. USDA notes the location of the infected flock is along the Mississippi flyway, a major migration corridor for wild waterfowl. Wild birds can carry and transmit the HPAI virus, and the upcoming spring migration could create an opportunity for the disease to spread.

Analysis at Tennessee’s Kord Animal Health Diagnostic Laboratory and the NVSL laboratory at Ames, Iowa confirmed the virus subtype as H7N9. Avian influenza viruses are classified by a combination of two groups of proteins: hemagglutinin and neuraminidase. There are 16 known hemagglutinin or “H” proteins and nine known neuraminidase or “N” proteins, with the proteins within each group identified by a number. Each combination of proteins within a virus is classified as a subtype, and genetically related strains within a subtype are referred to as a lineage. Thus the virus involved in the current outbreak is classified as the H7N9 subtype but a different lineage from the China H7N9 virus.

USDA encourages poultry owners and the general public to report sickness or unusual deaths among domestic or wild birds to State/Federal officials, either through their state veterinarian or through USDA’s toll-free number at 1-866-536-7593. 

Find more information about avian influenza on the USDA avian influenza page.