Michael Coston
Editor, Senior Moderator
Canada & U.S. Report Early Fall Uptick In H5N1 Outbreaks In Poultry
#18,871
In 2024, it wasn't until mid-October that we began seeing a significant uptick in North American poultry outbreaks due to the HPAI H5 virus. The following screenshot from the USDA (taken 10/17/24) shows only one outbreak in U.S. commercial poultry in the month of September.
By contrast, in the first 11 days of September 2025, the USDA has already confirmed 7 commercial (and 4 backyard) outbreaks.
Similarly, last year Canada went a full 6 months - (April 10th - Oct 21st) without reporting an HPAI outbreak in poultry (see screenshot below).
After a summer hiatus - this time of just under 4 months - this week Canada's CFIA this week is reporting 3 HPAI outbreaks in Alberta, nearly 6 weeks earlier than last year.
It is also notable that this summer the UK, and more recently Spain, have reported unusually high avian flu activity (see UK Defra: Heightened Avian Influenza Risk Warning Issued to Bird Keepers and Gamebird Rearers).
As we discussed at length last month in H5Nx: Reassort & Repeat, in the Northern hemisphere millions of migratory birds spend their summers in their high latitude breeding areas in Alaska, Canada, Siberia, and even the Arctic.
More than 200 bird species roost in the Alaskan Arctic Refuge (see map at top of blog), after which they migrate south each fall via four North American Flyways.
During their stay, they hatch a new generation of (flu naive) fledglings while mingling with other species, potentially sharing avian viruses picked up the previous spring (see 2016's Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1).
These factors can promote the creation and spread of new reassortants (genetic hybrids). While most are genetic failures - and unable to compete with existing strains - every once in a while a `new and improved' virus appears.
Two years ago (fall/winter 2023) we saw a new H5N1 B3.13 genotype emerge that could efficiently infect dairy cattle, while mildly infecting dozens of humans. Although not as well adapted to poultry, some spillovers were reported.
Last fall (2024), we saw 4 new genotypes emerge (D1.1, D1.2, D1.3), with D1.1 producing more severe illness in humans, while Canada experienced a multi-farm outbreak of emerging N1 genotype that was highly resistant to NAI antivirals.
Although past performance is no guarantee of future results, since HPAI H5N1 arrived in North America in 2021, more than 100 genetically distinct genotypes have emerged.
Another thing we are watching is the slow incursion of HPAI H5N5 - which has been reported in both Canada and Northern Europe (see Svalbard: HPAI H5N5 Detected In Arctic Foxes) - into the United States.
The USDA currently only lists 23 detections (in wild birds) across 4 states (primarily Massachusetts, along with Connecticut, Maine, and Michigan), but given the limits of surveillance and testing, this likely underrepresents its range and impact.
Given the surge of reports over the past few weeks, it is not too early for poultry producers, dairy farmers - and other stakeholders - to seriously consider now how they will deal with the likely return of avian flu this fall.
And any surprises that it might bring.
https://afludiary.blogspot.com/2025/09/canada-us-report-early-fall-uptick-in.html
#18,871
In 2024, it wasn't until mid-October that we began seeing a significant uptick in North American poultry outbreaks due to the HPAI H5 virus. The following screenshot from the USDA (taken 10/17/24) shows only one outbreak in U.S. commercial poultry in the month of September.
By contrast, in the first 11 days of September 2025, the USDA has already confirmed 7 commercial (and 4 backyard) outbreaks.
Similarly, last year Canada went a full 6 months - (April 10th - Oct 21st) without reporting an HPAI outbreak in poultry (see screenshot below).
After a summer hiatus - this time of just under 4 months - this week Canada's CFIA this week is reporting 3 HPAI outbreaks in Alberta, nearly 6 weeks earlier than last year.
It is also notable that this summer the UK, and more recently Spain, have reported unusually high avian flu activity (see UK Defra: Heightened Avian Influenza Risk Warning Issued to Bird Keepers and Gamebird Rearers).
As we discussed at length last month in H5Nx: Reassort & Repeat, in the Northern hemisphere millions of migratory birds spend their summers in their high latitude breeding areas in Alaska, Canada, Siberia, and even the Arctic.
More than 200 bird species roost in the Alaskan Arctic Refuge (see map at top of blog), after which they migrate south each fall via four North American Flyways.
During their stay, they hatch a new generation of (flu naive) fledglings while mingling with other species, potentially sharing avian viruses picked up the previous spring (see 2016's Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1).
These factors can promote the creation and spread of new reassortants (genetic hybrids). While most are genetic failures - and unable to compete with existing strains - every once in a while a `new and improved' virus appears.
Two years ago (fall/winter 2023) we saw a new H5N1 B3.13 genotype emerge that could efficiently infect dairy cattle, while mildly infecting dozens of humans. Although not as well adapted to poultry, some spillovers were reported.
Last fall (2024), we saw 4 new genotypes emerge (D1.1, D1.2, D1.3), with D1.1 producing more severe illness in humans, while Canada experienced a multi-farm outbreak of emerging N1 genotype that was highly resistant to NAI antivirals.
Although past performance is no guarantee of future results, since HPAI H5N1 arrived in North America in 2021, more than 100 genetically distinct genotypes have emerged.
Another thing we are watching is the slow incursion of HPAI H5N5 - which has been reported in both Canada and Northern Europe (see Svalbard: HPAI H5N5 Detected In Arctic Foxes) - into the United States.
The USDA currently only lists 23 detections (in wild birds) across 4 states (primarily Massachusetts, along with Connecticut, Maine, and Michigan), but given the limits of surveillance and testing, this likely underrepresents its range and impact.
Given the surge of reports over the past few weeks, it is not too early for poultry producers, dairy farmers - and other stakeholders - to seriously consider now how they will deal with the likely return of avian flu this fall.
And any surprises that it might bring.
https://afludiary.blogspot.com/2025/09/canada-us-report-early-fall-uptick-in.html
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