Study: H5N1 primarily spread by wild birds and waterfowl

H5N1, the virus that causes avian influenza, is now circulating consistently in wild birds and waterfowl in North America, according to a study published late last year in the journal Nature.

Virologists at the University of Pennsylvania studied samples of the virus' genome to trace how H5N1 evolved and spread across the continent in the early 2020s. They determined that most outbreaks of avian influenza in domestic birds were driven by exposure to infected wild birds, especially waterfowl. Backyard poultry showed signs of infection on average nine days earlier than commercial flocks, but do not appear to be the source of larger outbreaks in commercial poultry, according to the study.