An outbreak of highly pathogenic avian influenza has spread through chicken and turkey flocks in 46 states since it was first detected in Indiana on Feb. 8, 2022. The outbreak is also taking a heavy toll in Canada and Europe.
Better known as bird flu, avian influenza is a family of highly contagious viruses that are not typically harmful to most wild birds that transmit it, but are deadly to domesticated birds. The virus spreads quickly through poultry flocks and almost always causes severe disease or death, so when it is detected, officials quarantine the site and cull all the birds in the infected flock.
As of early November, this outbreak had led to the culling of over 50 million birds from Maine to Oregon, driving up prices for eggs and poultry – including holiday turkeys. This matches the toll from a 2014-2015 bird flu outbreak that previously was considered the most significant animal disease event in U.S. history. Yuko Sato, an associate professor of veterinary medicine who works with poultry producers, explains why so many birds are getting sick and whether the outbreak threatens human health.
Why is avian influenza so deadly for domesticated birds but not for wild birds that carry it?
Avian influenza (AI) is a contagious virus that affects all birds. There are two groups of aviain influenza viruses that cause disease in chickens: highly pathogenic AI (HPAI) and low pathogenic AI (LPAI).
HPAI viruses cause high mortality in poultry, and occasionally in some wild birds. LPAI can cause mild to moderate disease in poultry, and usually little to no clinical signs of illness in wild birds.
The primary natural hosts and reservoir of AI viruses are wild waterfowl, such as ducks and geese. This means that the virus is well adapted to them, and these birds do not typically get sick when they are infected with it.
But when domesticated poultry, such as chickens and turkeys, come in direct or indirect contact with feces of infected wild birds, they become infected and start to show symptoms, such as lethargy, coughing and sneezing and sudden death.