#18,262
One of the more remarkable `features' to the new and improved HPAI H5N1 virus that began its world tour in 2020 is that it has greatly expanded its host range; both in mammals and in wild birds.
But by February 2022, birds of prey/raptor (Accipitriformes) made up nearly 25% of the detections, and by the following summer Suliformes and Charadriiformes (shore birds) dominated.As the chart above shows, in the fall of 2021 the virus primarily impacted Anseriformes (waterfowl, such as ducks, geese, and swans) in the UK.
The wild bird species ‘order shift’ observed between November 2021 and June 2022 (Figure 2) reflects the spread of HPAIV infection from migratory water birds to native, sedentary wild bird species, including now seabird populations, which is unprecedented.
We've seen similar shifts here in the United States, and around the world, albeit with differences in timing and species. HPAI H5N1 - which previously spread primarily via asymptomatic waterfowl, and inflicted most of its damage on gallenacious birds (poultry) - was suddenly far deadlier to wild and migratory birds.
This was in sharp contrast to the first H5Nx epizootic in North America (2014-2015) where remarkably few wild birds were affected, and which vanished completely over the summer of 2015 (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl).
This shift from migratory waterfowl to other avian species has allowed the virus to persist even through the summer months in many locations, and has helped ensure its vigorous return each fall since 2021. It has also taken a serious toll on many wild bird populations.
Birds of prey (including scavengers like Vultures & Condors) have been particularly hard-hit because they can contract the virus from other birds, and from consuming small mammals that also carry the virus.
Last year - after a spate of reported deaths - we followed the efforts to protect the nearly extinct California Condor with an experimental H5N1 vaccine (First FWS 2024 Update on California Condor H5N1 Vaccination Trial).
The USDA's list of (known) H5N1 wild bird infections/deaths lists more than 600 bald eagles, more than 500 hawks, more than 400 owls, and scores of falcons affected by the virus, most of which were fatal. Given the number of birds that die unseen in the wild, and varying levels of surveillance, we can assume these numbers only represent a fraction of HPAI's impact.
I've provided the link, abstract, and a few excerpts below. Follow the link to read the report in its entirety.Today we've a preprint from researchers working at the (University of Minnesota) Raptor Center in St. Paul, MN and the Hawk Ridge Bird Observatory in Duluth, MN which finds that despite all of these reported deaths, some of these birds of prey appear (based on antibody levels) to have been infected, and have recovered.
Exposure and Survival of Wild Raptors During the 2022-2023 Highly Pathogenic Influenza A Virus Outbreak
Kelsey M. Rayment, Dana Franzen-Klein, Elizabeth Kurimo-Beechuk, and 8 more
This is a preprint; it has not been peer reviewed by a journal.
https://doi.org/10.21203/rs.3.rs-4759859/v1
This work is licensed under a CC BY 4.0 License
Abstract
The global outbreak of clade 2.3.4.4b H5N1 highly pathogenic influenza A virus (HP H5N1) has had an unprecedented impact on wild birds including raptors, but long-term population impacts have not been addressed. To determine if raptors survive infections with HP H5N1, raptors from the upper Midwest United States were serologically tested for antibodies to influenza A virus (IAV), H5 and N1.Raptors were sampled at The Raptor Center’s (University of Minnesota) wildlife rehabilitation hospital and at Hawk Ridge Bird Observatory. Samples were tested for IAV antibodies using a commercially available blocking ELISA, with positive samples tested for antibodies to H5 and N1.
Antibodies to IAV were detected in 86 individuals representing 7 species. Antibodies to H5 and N1 were detected in 60 individuals representing 6 species. Bald eagles had the highest seroprevalence with 67/97 (69.1%) seropositive for IAV and 52 of these 67 (77.6%) testing positive for antibodies to both H5 and N1.Prevalence of antibodies to IAV observed in this study was higher than reported from raptors sampled in this same region in 2012. The high prevalence of antibodies to H5 and N1 indicates a higher survival rate post-HP H5N1 infection in raptors than previously believed.
(SNIP)
Discussion
The results of this study provide evidence that raptor species in the upper Midwest, United States have been infected with and survived infection with HP H5N1. The three most represented species that tested positive for antibodies to H5 and N1 included: bald eagles (65/93, 69.9%), red-tailed hawks (Buteo jamaicensis) (7/57, 12.3%), and great horned owls (Bubo virginianus) (5/34, 14.7%).
These three species also had the highest prevalence of RT-PCR positive test results at the time of admission during active patient surveillance conducted at TRC in 2022, during the height of transmission of the virus9 .
Bald eagles had the highest H5 and N1 seropositivity compared to all other species tested. This could be due to a multitude of factors including the impact of natural history and diet on exposure risk, and differences in disease susceptibility between species9,13,21,22.
Other species that tested seropositive to IAV subtypes H5 and N1 include rough-legged hawks (Buteo lagopus), red-tailed hawks, turkey vultures (Cathartes aura), and great horned owls, all of which have been reported to feed on carrion or hunt wild waterfowl which are likely routes of exposure 22.
Some of the species that tested seropositive in this study included very few representative individuals, which precludes the ability to draw any conclusions about the regional population. For example, seroprevalence in rough-legged hawks was 25%, but only four individuals were tested and only one bird tested positive for antibodies to H5 /N1.
While the survival of some of these birds of prey is certainly welcome news, this study only provides us with data taken from a relatively small cohort sampled from a limited geographic region of the upper American Midwest, and may not represent what is going on in other places in the country, and around the world.
There are scores of genotypes of HPAI H5N1 in circulation around the world, with some being more pathogenic to certain species than others. It is possible that these survivors were lucky, in that they may have been exposed to a `milder' strain.
Hopefully, once recovered, these survivors will carry some immunity against future exposures. But the virus continues to evolve rapidly, making predictions about what happens next difficult.
Stay tuned.
