By R. M. Fulton, DVM, PhD, DACPV, Professor of Avian Diseases

Chicken With Fence In Background

In late 2021, a highly pathogenic avian influenza virus (HPAI) H5N1 virus was detected in domestic poultry in North America, first in an exhibition poultry flock in Newfoundland and Labrador. By mid-January, the virus was found in a backyard flock in Newfoundland and Labrador, and in hunter harvested waterfowl in North and South Carolina, Virginia, Maryland, and Florida. By February 2022, the same virus was detected in a small flock and a commercial turkey flock in Nova Scotia. Days later, the United States confirmed this same Eurasian H5N1 virus in a commercial turkey flock in southwestern Indiana. Within just 10 days, it was subsequently found in commercial broiler chickens in Kentucky, and backyard flocks in Virginia, New York, and Maine. This is a rapidly evolving situation and new detections continue to emerge as waterfowl migrate.

As backyard flocks have grown in popularity, many veterinary practices in suburban and urban areas now have clients who have poultry at home. While these clients may not seek care for their birds, veterinary professionals have an opportunity to share information about biosecurity practices and diseases of concern. As the saying goes, knowledge is power, and veterinary practitioners can help share these important messages with clients, family, friends, and their community to support early detection and response to an incursion of HPAI into their region.

Avian Influenza: Importance of Understanding the Genetics

In poultry, avian influenza viruses are referred to as either low pathogenic avian influenza (LPAI) or highly pathogenic avian influenza (HPAI), depending on the severity of disease the virus causes in domestic poultry. Avian influenza was not considered a major public health concern until 1997, when a novel HPAI strain caused significant disease in both poultry and humans in Hong Kong. The emergence of this virus raised awareness of the potential human health impact of HPAI outbreaks in poultry. It is important to note that no human cases of these avian influenza viruses have been detected in the United States.

Influenza viruses are classified by two surface proteins, the hemagglutinin protein (H) and neuraminidase protein (N). Currently, 18 H types (of which 16 can infect birds) and 11 N types are recognized, creating the possibility of 176 avian influenza viruses. Most, if not all, of these viruses will cycle among migratory waterfowl with little or no indication of causing disease in those species although infected animals may shed the virus in feces for extended periods. However, a subset of viruses with the H5 or H7 protein can cause significant disease if introduced to domestic poultry; these viruses are given the designation of HPAI. Importantly, not all H7 or H5 viruses prove to be highly pathogenic in poultry and are subsequently classified as LPAI. However, LPAI H5 and H7 viruses can switch from LPAI to HPAI and in some cases, to develop the capability to cause catastrophic poultry disease almost overnight, in a phenomenon known as antigenic shift.

Antigenic shift occurs when an animal is infected with multiple influenza viruses that subsequently reassort, creating novel strains. Historically, it was believed that swine serve as the required “mixing vessel,” as swine are susceptible to swine, human and avian influenza viruses, creating the greatest opportunity for emergence of a novel virus with capability to cause disease in multiple species. The emergence of the 1997 HPAI in Hong Kong directly demonstrated that genome reassortment is common in waterfowl which is believed to be the source of that virus. Viruses that arise from reassortment or antigenic shift are particularly concerning as they have the potential to cause pandemics, because affected populations that may have little natural immunity or existing vaccines to confer protection.

Antigenic drift, in contrast, is a slower process driven by mutations to H, and less commonly N, and is often caused by vaccination pressures. Progressive changes to the H protein can shift virus behavior, leading to enhanced disease-causing capabilities, and in some cases to transition a virus classified as LPAI to HPAI.

Avian Influenza: A Virus on the Move

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The emergence and spread of avian influenza viruses, both LPAI and HPAI, is closely linked to the movement of migratory waterfowl travel along flyways analogous to highways in the sky for birds. The flyways that cross the United States of America from north to south are the Pacific, Central, Mississippi, and Atlantic. Birds on the Pacific flyway mix with birds from the East Asia/Australia flyway in Alaska. Birds on the Atlantic flyway mix with the East Atlantic flyway which originate in eastern Europe and western Africa. Migratory birds on Central and Mississippi flyways do not mix with those on the European or Asian origin flyways directly but indirectly through exposure to birds on the Atlantic and Pacific flyways, respectively.

Michigan has seen its fair share of avian influenza, particularly near Lake Michigan in western Michigan. In 2002, LPAI H5N1 was discovered in a turkey flock during routine pre-slaughter blood testing and again in 2006, during routine testing of wild Mallard ducks. The same LPAI H5N1 was found later in a Michigan raise-for-release domesticated Mallard duck flock.

Michigan was not affected when a Eurasian H5 virus carried by migratory waterfowl combined with a North American N2 and caused a severe outbreak of HPAI in midwestern poultry in 2014-2015. It was first detected in British Columbia and subsequently spread through Washington and northern California along the Pacific flyway. During early and late spring 2015, the virus arrived in Missouri and spread to Minnesota, Iowa, and Wisconsin along the Mississippi and Central flyways. That devastating outbreak resulted in 48 million dead or depopulated poultry on 160 turkey farms, 46 egg laying chicken farms, and 21 backyard flocks. Of the affected egg laying farms, seven had over 3.5 million chickens each. Initial introduction was from infected migratory waterfowl, but later spread was due to human activity. The only detection in Michigan during that outbreak was a similar HPAI H5N1 found in a flock of Canada geese in the Detroit suburbs.

What Should Poultry Owners Do?

  • Keep birds inside the coop when waterfowl are migrating. Note that Michigan and some other states have resident Canada geese flocks that do not migrate.
  • Observe flocks for signs of illness. HPAI causes many birds to die at the same time and those remaining in the flock will appear sick. An individual bird coughing or sneezing is not a cause for worry. Sick birds will be inactive, act sleepy, and quit eating.
  • If a sudden death loss occurs in a flock (2 to 3 dead birds out of a flock of 10), multiple birds paralyzed at the same time or with twisted necks, immediately contact State/Federal officials, either through their state veterinarian or through USDA’s toll-free number at 866.536.7593. In Michigan, contact the Michigan Department of Agriculture and Rural Development at 800.292.3939 (daytime) or 517.373.0440 (after-hours).
  • Always practice good biosecurity. Basically, biosecurity means keeping disease away from your flock by keeping the outside out and the inside in.
  • Have dedicated clothing and footwear to wear only when taking care of birds. At a minimum, change shoes before entering the coop.
  • If owners hunt migratory waterfowl or golf, have someone else take care of the flock for a period of 72 hours after potential exposure to wild birds.
  • For more information on protecting flocks with biosecurity measures, visit USDA’s Defend the Flock site for tools, resources, and more.

The Michigan State University Veterinary Diagnostic Laboratory assists state and federal agencies in disease investigations by providing testing for diseases such as avian influenza. The Laboratory also performs postmortem examinations to help identify health issues in flocks. Veterinarians or owners experiencing limited losses can contact the Laboratory at 517.353.1683 for information on how to submit an animal for a post-mortem examination.


Types of influenza viruses., accessed 7 Feb 2022.

Detection of high pathogenic avian influenza (H5N1) in Newfoundland and Labrador 2021 and Nova Scotia 2022., accessed 7 Feb 2022.

2022 Highly Pathogenic Avian Influenza., accessed 9 Feb 2022.

Editor’s note:

A version of this article was published in the Spring 2022 issue of The Michigan Veterinarian, published by the Michigan Veterinary Medical Association.

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