#18,951
Although cattle, goats, alpaca, and sheep have only recently proved their susceptibility to HPAI H5 infection, for the past 2 decades the big livestock concern has been H5's potential to infect and adapt to swine.While detections in swine have been limited, we've seen scattered evidence that H5N1 can infect pigs, albeit often asymptomatically. A few past reports include:In May of 2023, in Netherlands: Zoonoses Experts Council (DB-Z) Risk Assessment & Warning of Swine As `Mixing Vessels' For Avian Flu, we looked at growing concerns in Europe that avian H5N1 could increase its pandemic threat by spreading (and evolving) in farmed swine.
- An Unusual Report Of H5N1 in Pigs (Indonesia 2016)
Only days later, a report out of Italy confirming an H5N1 spillover event at a `mixed species' farm (poultry & swine), and the subsequent seroconversion of the majority of the pigs tested on that farm (see Study: Seroconversion of a Swine Herd in a Free-Range Rural Multi-Species Farm against HPAI H5N1 2.3.4.4b Clade Virus).Last November, we saw two pigs infected with a new, recently emerged genotype (D1.2) in Oregon (see USDA Confirms 2nd Pig on Oregon Farm Tested Positive for H5N1).
So far, studies have shown only limited susceptibility of swine to the H5N1 virus (see EID Journal: Low Susceptibility of Pigs against Experimental Infection with HPAI Virus H5N1 Clade 2.3.4.4b), but there are legitimate concerns that over time, a more `swine-adapted' strain could emerge.Surveillance and testing of commercially raised swine around the world is quite limited, and much of what happens with in the wild typically flies under our radar. But today we have a study which finds (limited) serological evidence of HPAI H5 infection in wild pigs in western Canada.
While the reported seroprevalence (<5%) was low, it may not fully represent the situation on the ground.
- First, because this was based on 267 wild pigs opportunistically trapped and euthanized across four Alberta counties between 2021–2024, with only 120 serum samples subjected to serological analysis.
- Second, the authors explain ` . . . this method likely excludes sick or debilitated individuals, as they may be less likely to approach traps. Notably, no dead wild pigs have been found or sampled.
- Third, the authors state ` . . . only a limited number of groups were removed during the IAV outbreak period, and sampling was not evenly distributed across the entire range of wild pigs.
Serological Evidence of Highly Pathogenic Avian Influenza (H5N1) in Invasive Wild Pigs in Western Canada
Oshin Ley Garcia, Tamiru Alkie, Frank van der Meer, Yohannes Berhane, Susan E. Detmer, Ishara Muhammadu Isham … See all authors
First published: 17 November 2025
https://doi.org/10.1155/tbed/2720469
Academic Editor: Nan-hua ChenSections
Abstract
Influenza A virus (IAV) can infect a wide range of hosts, including wild and domestic pigs. Swine play an important role in influenza evolution and epidemiology due to their ability to get infected with both avian and human influenza viruses, potentially leading to reassorted virus variants. Interactions at the wild-domestic swine interface have been documented on multiple occasions, raising concern about pathogen transmission and the emergence of novel influenza strains.This study investigates the occurrence and subtypes of IAV infecting invasive wild pigs in Alberta, Canada. A total of 267 wild pigs were captured between 2021–2024. Exposure to IAV was initially detected by cELISA, with further confirmation of exposure to the H5Nx virus by hemagglutination inhibition (HI) and virus neutralization (VN) assays.
Although no IAV genetic material was detected by qPCR, the seropositive samples by cELISA (4.17%; 5/120) coincided with the 2022–2024 highly pathogenic avian influenza virus (HPAI) H5N1 epizootic in Alberta, which involved outbreaks in wild species and domestic birds.These findings, combined with the epidemiological context, suggest interspecies transmission of HPAI H5N1 clade 2.3.4.4b to wild pigs. These results highlight the potential role of wild pigs as a new host in Canada and emphasize the need for continued surveillance of IAV in wild pig populations to assess the risk of spillover events at the wildlife, livestock, and human interfaces.
(SNIP)
5. Conclusion
In summary, this study provides evidence of exposure of wild pigs to HPAI H5N1, likely originating from the concurrent epizootic in wild birds, domestic poultry, and other wildlife species, suggesting interspecies transmission of HPAI H5N1 viruses. Although serological evidence of IAV infection was observed at low prevalence in the wild pig population in Alberta, these findings raise important questions about the potential role of wild pigs in the ecology of HPAI H5N1 viruses in Canada and across North America.
In the context of recurring outbreaks of H5N1, the possibility that invasive wild pigs could act as a mixing vessel and contribute to the emergence of new reassortants highlights the need for ongoing genomic surveillance and targeted research.
While the number of wild pigs in Canada is a matter of some debate, it almost certainly reaches into the tens of thousands, and their population - and range - are growing rapidly (see Wild Pigs Invasive Species Centre).
In the United States, estimates run in 6-9 million range, mostly clustered across the Southern tier of states (see APHIS Map below).
Three months ago, in Frontiers Vet. Sci (Review): Emerging Threats of HPAI H5N1 Clade 2.3.4.4b in Swine, we looked at study commissioned by the Swine Health Information Center (SHIC), which examined how commercial and wild pigs could potentially serve as `mixing vessels' for the H5N1 virus.
The authors wrote:
The expanding host range and ongoing evolution of HPAI H5N1 clade 2.3.4.4b highlight the urgent need for comprehensive surveillance, preparedness strategies, and support for scientific investigations.
According to the USDA, as of Sept.1, there were 74.5 million hogs and pigs on U.S. farms, and according to their last published Influenza A Virus in Swine Surveillance report, during Q2 they received 925 samples:
A total of 259 samples were subtyped, including H1N1 (n=85), H1N2 (n=101), H3N2 (n=61), H3N1 (n=1), and mixed subtype (n=11).The USDA further notes:
Due to the voluntary nature of this surveillance, the information in this report cannot be used to determine regional and/or national incidence, prevalence, or other epidemiological measures, but it may help identify IAV-S trends.The common appeal across the hundreds of epidemiological studies we've looked at on this blog is that more robust surveillance, testing, and sharing of data is essential (see here, here, here, here, here, here, and here), yet, progress remains painfully slow.
Health Agencies like the WHO, PAHO, ECDC, and others issue frequent pleas and reminders to member states to share data, but local economic and political considerations often take precedence.The world continues to treat the spread of HPAI primarily as an agricultural threat, rather than a potential public health concern. A policy that may pay benefits in the short run, but could prove quite costly over time.