Avian influenza is an infectious disease of birds caused by a group of influenza A viruses. These viruses naturally circulate in wild waterfowl and shorebirds, which typically carry the viruses without showing any signs of disease. Most of these avian influenza viruses are considered low-pathogenic (LPAI) strains that cause little or no clinical signs in any species. However, LPAI strains may naturally mutate into strains that do cause severe disease in birds (and sometimes other species). These disease-causing strains are the highly pathogenic (HPAI) strains that have caused severe disease and high mortality in birds, especially domestic poultry.
New HPAI Strain in 2021-2022
In the winter and spring of 2021-2022, an outbreak of Highly Pathogenic Avian Influenza (HPAI) involving a new strain of H5N1 emerged in North America. Unlike prior strains of HPAI in North America, this particular strain is causing widespread mortality in some species of wild birds, particularly in snow geese, raptors, and vultures. This strain has also caused mortality in several mammal species, especially in skunks and foxes. For more information on HPAI in mammals, please visit the U.S. Department of Agriculture (USDA) website.
Early Colorado Cases
This strain of HPAI was first confirmed in wild geese in Northeast Colorado in March of 2022. From March through November 2022, HPAI mortalities were documented in a number of raptors, waterfowl, and vultures in numerous locations throughout the state. Most reports were of limited mortalities involving individual birds or small numbers of birds and there was one mortality in a striped skunk. All confirmed HPAI cases in Colorado (both domestic and wild) can be viewed on maps available at the Colorado Department of Agriculture website.
In late November 2022, Colorado Parks and Wildlife (CPW) began receiving increasing reports of sick and dead snow geese in Northeastern Colorado associated with large-scale HPAI mortality events. CPW personnel documented mortalities in excess of 1,000 birds on multiple waterways in Morgan and Logan Counties. Shortly thereafter, large-scale mortalities began occurring in southeast Colorado in Kiowa, Bent, Otero, and Prowers counties. Total snow geese mortality numbers are unknown, but mortality reports range from a single animal to more than 1,000 dead geese on a single reservoir. These mortality events coincide with fall migrations of birds leading to large congregations of snow geese in Colorado.
At the national level, outbreaks in wild birds and poultry continue to rise and the U.S. is approaching a record number of birds affected compared to previous bird flu outbreaks. To date, HPAI has been detected in all four North American migration flyways. It is expected that the disease will persist through spring migrations.
Coordinated Multi-Agency Effort
Concern for HPAI in wild birds, domestic poultry, humans, and the environment overlaps multiple state and federal agencies. Colorado Parks and Wildlife is coordinating with the Colorado Division of Homeland Security and Emergency Management, Colorado Department of Agriculture (CDA), United States Department of Agriculture (USDA), and Colorado Department of Public Health and Environment (CDPHE) to share available data and coordinate response plans.
Frequently Asked Questions
Additional Avian influenza Resources
Additional information on avian influenza can be found at the following: