#18,064
One of the problems with trying to draw conclusions about the threat posed by HPAI H5 clade 2.3.4.4b is that there are multiple subtypes (H5N1, H5N5, H5N6, etc.) - and scores of genotypes - circulating concurrently around the globe.
The H5 virus infecting cattle in America is related to - but is genetically distinct from - the H5 viruses infecting sea lions in Chile, farmed mink in Spain, raccoons in Nova Scotia, or cats in Poland.
Complicating matters, these viruses continue to evolve slowly via antigenic drift, and generate new genotypes through antigenic shift (reassortment). HPAI H5 is a continually moving target, meaning past performance does not guarantee future results.
Most of this viral evolution occurs outside of our view, either in remote regions of the world, or in hosts that are difficult to sample. Even in more accessible regions, many countries are either ill-equipped - or unwilling - to conduct extensive testing.
Fortunately, the vast majority of these evolutionary changes will do little to enhance the virus, and many will actually prove a detriment. Most of these viral GOF experiments will fail to thrive, and wither away into obscurity.
None of this is to diminish the importance of studies that can only look at a small slice of HPAI H5 conducted over a brief moment in time, but it is important we realize their limitations.
A seroprevalence study of cattle in the United States six short months ago would have likely reassured us that cattle were not susceptible to H5N1. Things change.
With that in mind we have the following study, published this week in the CDC's EID journal that finds low - but significant - number of hunting dogs with antibodies to H5N1 tested over a 2 month period in 2023.
The authors make it abundantly clear, that this study applies to `subclade 2.3.4.4b H5N1 HPIAV strains that circulated in North America during 2022–2023'.
Due to its length, I've only posted some excerpts (reformatted for better readability). Follow the link to read it in its entirety. I'll have a brief postscript after the break.
Antibodies to Influenza A(H5N1) Virus in Hunting Dogs Retrieving Wild Fowl, Washington, USA
Justin D. Brown, Adam Black, Katherine H. Haman, Diego G. Diel, Vickie E. Ramirez, Rachel S. Ziejka, Hannah T. Fenelon, Peter M. Rabinowitz, Lila Stevens, Rebecca Poulson, and David E. Stallknecht
Abstract
We detected antibodies to H5 and N1 subtype influenza A viruses in 4/194 (2%) dogs from Washington, USA, that hunted or engaged in hunt tests and training with wild birds. Historical data provided by dog owners showed seropositive dogs had high levels of exposure to waterfowl.
(SNIP)
Despite the prolonged global epizootic of HPIAV H5N1, reported infections in dogs have been rare.
- During an HPIAV H5N1 outbreak in Thailand, a fatal canine infection in 2004 associated with a dog eating a duck carcass was reported (1).
- A follow-up serosurvey of outwardly healthy stray dogs in Thailand detected HPIAV H5N1 antibodies in 25.4% (160/629) of sampled dogs (2).
- During April 2023, another fatal HPIAV H5N1 infection was identified in Ontario, Canada, in a dog that developed severe respiratory and systemic signs shortly after chewing on a dead wild goose (3).
- In experiments, beagles were susceptible to HPIAV H5N1 infections, during which some infected dogs excreted high concentrations of virus through the respiratory tract and experienced severe disease (4).
- In contrast, previous studies in beagles reported susceptibility to HPIAV H5N1 infection that manifested with moderate to no clinical signs (5,6).
Existing field and experimental data collectively suggest dogs are susceptible to HPIAV H5N1 infection but clinical outcomes vary. However, infection appears to be restricted to dogs with high virus exposure. To investigate this further, we tested for antibodies to influenza A(H5N1) virus in bird hunting dogs, a category of dogs at high risk for contact with HPIAV H5N1–infected wild birds, and compared serologic results to reported hunting or training activities.
Dog owners completed a questionnaire providing details about their dogs’ retrieving activities, canine influenza virus (CIV) vaccination status, and clinical history. Methods used in this research were approved by the Institutional Animal Care and Use Committee at Penn State University (#202302394).
During March–June 2023 in Washington, USA, we collected blood samples from 194 dogs identified by owners as having engaged in bird hunting or bird hunt tests and training over the previous 12 months (Figure). Waterfowl hunting season in Washington extends from mid-October through February; consequently, we collected samples 1–4 months after season closure. We collected blood from the jugular vein, immediately centrifuged it, and stored it at 4ºC in the field, then stored serum at –20°C until testing was performed.
(SNIP)
We used conservative positive threshold titers: H5 HI, >1:32; H5 VN, >1:20; and N1 ELLA, >1:80. We considered samples H5 seropositive if positive for H5 using HI assay or VN and N1 seropositive if positive for N1 using ELLA. We also tested all bELISA-positive serum samples for antibodies to H3N2 and H3N8 CIV by HI assay (positive threshold ≥1:8) (9). We calculated seroprevalence using R (10).
Most dogs retrieved waterfowl (86%), and many (69%) retrieved both waterfowl and upland game birds (Appendix Tables 1, 2). Dogs most commonly contacted dabbling ducks (81% of dogs), which are notable reservoirs for HPIAV H5N1. Dogs also frequently contacted birds from other categories considered high risk for HPIAV H5N1, including geese (32% of dogs) and diving ducks (23% of dogs) (Appendix Table 3). Most dogs had retrieved or trained multiple times during the previous 12 months; 38% were reported to have been in the field during ≥15 hunts and 78% reported to have trained with live or dead birds ≥15 times (Appendix Table 2). Reportedly 11% of dogs retrieved dead or clinically ill waterfowl that showed no evidence of having been shot or hunted.
(SNIP)
Over the previous 12 months, all 4 H5- and N1-seropositive dogs reportedly had hunted waterfowl extensively in areas affected by H5N1 HPIAV outbreaks in wild waterfowl. Three H5- and N1-seropositive dogs reportedly had retrieved waterfowl that were either dead or had neurologic symptoms but that showed no evidence of having been shot or hunted.
Two H5- and N1-seropositive dogs were from households that owned multiple hunting dogs included in this study; 1 seropositive dog was 1 of 2 dogs included in the study and the other was 1 of 3. None of the other tested dogs from those multidog households were seropositive for IAV.
Conclusions
We detected antibodies to H5 and N1 only in hunting dogs with high levels of bird hunting and waterfowl retrieval. Although that finding suggests transmission of HPIAV H5N1 from waterfowl to dogs can occur, low seroprevalence, lack of reported disease in seropositive dogs, and lack of evidence for dog-to-dog transmission among dogs sharing households collectively indicate that the subclade 2.3.4.4b H5N1 HPIAV strains that circulated in North America during 2022–2023 were poorly adapted to dogs.
Those results suggest that effective risk communication with hunting dog owners could be an inexpensive and effective strategy to reduce the potential for spillover to dogs, and monitoring hunting dogs for IAV could be a useful addition to existing surveillance efforts.
Dr. Brown is an assistant teaching professor in the Department of Veterinary and Biomedical Sciences in the College of Agricultural Sciences at Pennsylvania State University. His research focuses on defining the impacts of infectious diseases on wildlife populations.
Last month, in Microorganisms: Case Report On Symptomatic H5N1 Infection In A Dog - Poland, 2023, we looked at a much different case report, with the authors writing:
The case described in our report confirms that on rare occasions the A/H5N1 virus can also induce a natural severe respiratory disease in dogs. While in some of them the infection remains asymptomatic, capable of shedding the virus [35], others exhibit mild symptoms such as transient fever [34], or even fatal disease [20].
The authors also note:
In Poland, as in most European countries, dogs presenting with respiratory symptoms are not routinely tested for influenza.
Different country, different time, different genotype . . . different outcome.
While this is likely an outlier, the more I write about novel flu viruses, the less inclined I am to make blanket assumptions about what a given strain can - or can't - do.