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Avian influenza

Avian influenza (AI) is caused by a virus that is common in wild bird populations, especially waterfowl and shorebirds. Avian influenza viruses are identified by two specific protein groups: Hemagglutinin or the “H” of which there are 16 and neuraminidase or “N” of which there are 9. Combinations of these 2 create a subtype of the virus (ex: H1N1, H5N2, etc). There are many different subtypes of AI and in general, most subtypes do not cause obvious signs of disease in wild birds. Waterfowl often carry avian influenza viruses naturally in their gastrointestinal tract, often without causing disease, but there have been rare strains that may also cause disease in some wild birds (including some species of waterfowl) or other animals.

Avian influenza viruses can cause disease in domestic birds with the severity of the infection depending on the subtype and gene assortment of the virus that is involved. The pathogenicity identification (low or highly pathogenic avian influenza) refers to how lethal the identified type and strain of the virus is to domestic poultry.


Typically, avian influenza viruses are shed in the feces of wild birds that carry the virus and transmission between wild birds is believed to primarily occur through the ingestion of the virus. AI viruses typically increase in wild bird populations during the late summer and early fall pre-migration staging when previously un-exposed, juvenile birds begin to concentrate in areas with older ducks, many of which are carriers. When AI viruses cause disease, those birds often shed viruses from their respiratory tracts as well.


Signs of AI in wild birds vary depending on the viral subtype, environmental stress and bird species, and are not specific to the disease associated with this virus. In wild birds, infections with AI typically do not show any clinical signs. When birds do show clinical signs, they can be respiratory (sneezing, coughing, ocular and nasal discharge, edema surrounding the eyes); neurological (abnormal position of the head, falling or tremors, circling); gastro-intestinal (diarrhea, green discoloration of feces) and just overall signs of not doing well including weakness.


The department monitors for AI in free-ranging wild birds in Wisconsin throughout the year through investigations of wild bird mortality events involving five or more birds. The DNR, in cooperation with the USGS National Wildlife Health Center and others, has enhanced surveillance efforts based on apparent species susceptibility, reported clinical signs and proximity to any reported mortality events in wild birds.

Investigating sick or dead wild bird events is an effective tool for the early detection of AI outbreaks. If you observe five or more sick or dead birds in one area, please contact the DNR Wildlife Switchboard by emailing or calling 608-267-0866. You will need to leave a message for the switchboard staff to return your call. In your message, please include the number of animals, the species (such as Canada goose), if they were sick or dead, the specific location where you saw them, including the county and your contact information.


Sometimes, avian influenza viruses can cause other species of animals to become sick. In Wisconsin, the strain of H5N1 HPAI affecting wild and domestic birds in 2022 has been linked to a few cases of the disease in wild mammals including red foxes, bobcats, fishers, skunks and otters. Mammal species that may scavenge or hunt wild birds as part of their natural diet are likely exposed to the virus from eating infected wild birds. All of these affected mammals showed neurological signs. Neurological signs in mammals can signify many different conditions, including exposure to environmental contaminants, parasitic infections and diseases such as canine distemper and rabies. People should avoid approaching any wild mammal that appears sick, injured or behaving abnormally.


For information on symptoms of avian influenza in humans and related resources please visit Human health and Avian Influenza A (H5N1) Virus [exit DNR]

The majority of AI viruses do not infect humans, however, simple precautions should be taken to reduce or minimize the risks of infection.

  • Do not handle sick or dead wild birds.
  • Wash hands thoroughly with soap and water after contact with a wild bird or contaminated surfaces (including birdbaths and feeders). Flu viruses are inactivated by common disinfectants including detergents, 10% bleach solution and alcohol.
  • Cook all meat, including wild birds and poultry thoroughly to a temperature of 165° F to kill organisms and parasites.
  • Hunters should sanitize all tools and surfaces when handling, cleaning and preparing wild birds.
  • Wear disposable gloves when cleaning bird feeders and baths.