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The North American migratory birds that flew south last fall are beginning to work their way north again towards their summer high-latitude roosting areas (primarily in Northern Canada and Alaska). With millions of birds on the move again, there is an increased risk of H5N1 impacting poultry farms along their route.
First the warning from the Wisconsin Department of Agriculture, Trade, and Consumer Protection, after which we'll take a slightly longer view.While the immediate concern is for commercial poultry flocks that might be affected, there may be longer term implications as well.
DATCP Reminds Poultry Owners of Increasing Threat of Avian Influenza
FOR IMMEDIATE RELEASE: March 8, 2023
Contact: Kevin Hoffman, Public Information Officer, (608) 224-5005, kevin.hoffman@wisconsin.gov
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MADISON, Wis. — The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) is reminding poultry owners of the ongoing threat of highly pathogenic avian influenza (HPAI). The spring migratory period for wild birds brings an increased risk of infection to all flocks, so DATCP recommends that poultry owners continue using the strongest biosecurity measures to protect their birds.
In Wisconsin last year, 29 domestic flocks in 18 counties were confirmed with HPAI. Nationwide, more than 58.5 million birds have died related to HPAI making it the largest animal disease outbreak in U.S. history, surpassing the 2014-15 bird flu outbreak.
The best way to protect flocks from infection is through strong biosecurity practices that do not allow for virus introduction. All poultry owners, regardless of the size of the operation, must ensure that strict biosecurity practices are in place to prevent HPAI from infecting flocks. As the spring migration of wild birds begins, DATCP encourages all poultry producers to review and update their biosecurity plans. Those who do not have a biosecurity plan should work with their flock veterinarian to develop one that clearly addresses the risks for disease introduction specific to their operations. Biosecurity guides and other resources are available from the U.S. Department of Agriculture's Defend the Flock Program.
State law requires Wisconsin poultry and other livestock owners to register where their animals are kept. DATCP uses this information to rapidly respond to animal disease outbreaks to protect animal health, the food supply, public safety, and Wisconsin's agriculture economy. Registration is free and can be completed at wiid.org or by calling the Wisconsin Livestock Identification Consortium at (888) 808-1910.
Poultry owners who recognize any abnormal increase in mortality or clinical signs of disease, including respiratory distress, drop in food or water intake, decreased egg production, and lethargy are asked to report it to DATCP at (800) 572-8981.
Please visit hpai.wi.gov for regular updates on HPAI in Wisconsin and resources for poultry owners. More information on HPAI, prevention strategies and biosecurity is available here:
U.S. Poultry and Egg Association self-assessment of enhanced biosecurity
Wisconsin Department of Natural Resources: Avian influenza and wild birds
Wisconsin Department of Health Services: Avian influenza and humans
The fall (southbound) migration is generally regarded as the riskiest, since that is when we typically first see new subtypes or new genotypes of avian flu emerge.
- In 2016, a reassortment event over the summer in either China or Siberia led to a record setting fall H5N8 epizootic (see EID Journal: Reassorted HPAI H5N8 Clade 2.3.4.4. - Germany 2016) across much of Europe.
- The following fall (2017), an H5N6 subtype unexpectedly emerged in Europe (see Netherlands Bird Flu Identified As Reassorted H5N6).
- In the fall of 2020, once again in Pre-Print: Novel Incursion of a HPAI H5N8 Virus in the Netherlands, October 2020. we saw the arrival of a reassorted H5Nx virus.
H5N1 HPAI (2020-onwards)
- These H5N1 viruses were first detected in Europe in October 2020 after reassortment of H5N8 viruses with wild bird lineage N1 viruses.- Since Autumn 2021 there has been domination of the H5N1 clade 2.3.4.4b viruses with a relatively stable genotype- These viruses have spread globally with the movement of wild migratory birds and have reassorted with local low pathogenic viruses in many places.- In Africa these viruses were first detected in early 2021.- In late 2021 they were introduced into Asia- In late 2021 introduction into the Americas.- In 2022 Extensive infection in coastal seabirds and mass die offs of numerous ecologically important species of wild bird.- In mid 2022 the virus was first detected in Central America and late 2022 in South America in wild birds and poultry with the southwards migration of wild birds.
A study, published in 2016 (see Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1), suggests that migratory waterfowl can pick up new (or mutated) HPAI viruses in the spring (likely from poultry or terrestrial birds) on their way to their summer breeding spots - where they spread and potentially evolve - and then redistribute them on their southbound journey the following fall.
Until relatively recently, HPAI viruses had a hard time persisting in wild or migratory birds, and would rarely be seen over the summer. Birds either sickened and died quickly, or were immune to infection (see 2016's PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl).
It required the periodic reintroduction of HPAI strains - primarily from infected poultry - in order for migratory birds to propagate the virus. A big reason why it took nearly 20 years for H5N1 to make it from Southeast Asia to South America.
But the virus has changed in recent years, and many avian species are now able to carry, and spread HPAI H5 over long distances. That provides H5 more opportunities to interact with other avian (and non-avian) flu viruses, to infect new hosts, and either reassort or adapt into a bigger threat.
We've seen reports of numerous H5N1 genotypes emerging, both in Europe and the Americas, meaning there is an ever-increasing amount of viral diversity out there, providing a growing supply of genetic building blocks for the creation of new subtypes, genotypes, or variants of H5Nx.
All of which suggests that what we see arrive next fall may very well depend upon what viruses migratory birds encounter on their way north this spring.
Which means that even if we get lucky enough to see a lull in avian flu over the summer, we need to be prepared for new challenges next fall.
