Bird flu decimated tern colony in northwest Washington
Study findings provide new details on a Caspian tern die-off near Port Townsend in 2023 and how the virus killed seals in the region, infecting their brains.
By: Bill Lucia - November 18, 2024 4:00 am
More than half a colony of Caspian terns on a small island near Port Townsend died last year amid an outbreak of bird flu, underscoring the harsh effects the disease can have on wildlife.
Researchers say they directly counted 1,101 dead adult terns and 520 dead chicks and that at least 53-56% of the adult birds in a colony on Rat Island, in northern Puget Sound, were wiped out. After factoring in Caspian tern deaths in other parts of the region, the researchers estimated about 10-14% of the birds in the Pacific flyway were lost last year to bird flu.
The researchers also studied harbor seals that died from the virus on or around Rat Island during the same timeframe and found that the disease had attacked the animals differently than it did birds, causing severe inflammation in their brains.
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https://washingtonstatestandard.com...ecimated-tern-colony-in-northwest-washington/
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ORIGINAL RESEARCH article
Front. Vet. Sci., 31 October 2024
Sec. Zoological Medicine
Volume 11 - 2024 |
https://doi.org/10.3389/fvets.2024.1483922
This article is part of the Research Topic
Insights in Zoological Medicine: 2023
View all 9 articles
A comprehensive epidemiological approach documenting an outbreak of H5N1 highly pathogenic avian influenza virus clade 2.3.4.4b among gulls, terns, and harbor seals in the Northeastern Pacific
Katherine H. Haman
Katherine H. Haman1*Scott F. PearsonScott F. Pearson1Justin BrownJustin Brown2Lauren A. FrisbieLauren A. Frisbie3Sara PenhallegonSara Penhallegon4Azeza M. FalghoushAzeza M. Falghoush5Rebecca M. WolkingRebecca M. Wolking5Brandi K. TorrevillasBrandi K. Torrevillas5Kyle R. Taylor,Kyle R. Taylor5,6Kevin R. Snekvik,Kevin R. Snekvik5,6Sarah A. TanedoSarah A. Tanedo1Ilai N. KerenIlai N. Keren1Elizabeth A. AshleyElizabeth A. Ashley7Casey T. ClarkCasey T. Clark1Dyanna M. LambournDyanna M. Lambourn1Chrissy D. Eckstrand,Chrissy D. Eckstrand5,6Steven E. Edmonds,Steven E. Edmonds5,6Emma R. Rovani-Rhoades,Emma R. Rovani-Rhoades5,6Hanna OlteanHanna Oltean3Kristin WilkinsonKristin Wilkinson8Deborah FauquierDeborah Fauquier9Allison BlackAllison Black3Thomas B. Waltzek,Thomas B. Waltzek5,6
1Wildlife Program, Science Division, Washington Department of Fish and Wildlife, Olympia, WA, United States
2Department of Veterinary and Biomedical Sciences, Pennsylvania State University, University Park, PA, United States
3Washington State Department of Health, Shoreline, WA, United States
4Center Valley Animal Rescue, Quilcene, WA, United States
5Washington Animal Disease Diagnostic Laboratory, Pullman, WA, United States
6Department of Veterinary Microbiology and Pathology, Washington State University College of Veterinary Medicine, Pullman, WA, United States
7EpiCenter for Disease Dynamics, One Health Institute, School of Veterinary Medicine, University of California Davis, Davis, CA, United States
8West Coast Regional Office, National Marine Fisheries Service, Seattle, WA, United States
9Office of Protected Resources, National Marine Fisheries Service, Silver Spring, MD, United States
Highly pathogenic avian influenza viruses (HPAIV) H5N1 clade 2.3.4.4b continue to have unprecedented global impacts on wild birds and mammals, with especially significant mortality observed in colonial surface-nesting seabirds and in some marine mammal species. In July of 2023 H5N1 HPAIV 2.3.4.4b was detected in Caspian terns nesting on Rat Island, Washington USA. An estimated 1,800–1,900 adult terns populated the breeding colony, based on aerial photographs taken at the start of the outbreak. On a near-weekly basis throughout July and August, we counted and removed carcasses, euthanized moribund birds, and collected swab and tissue samples for diagnostic testing and next-generation sequencing. We directly counted 1,101 dead Caspian tern adults and 520 dead chicks, indicating a minimum 56% loss of the adult colony population and potential impacts to reproductive success. Combining the observed mortality on Rat Island with HPAI-related Caspian tern deaths recorded elsewhere in Washington and Oregon, we estimate that 10–14% of the Pacific Flyway population was lost in the summer of 2023. Comparatively few adult Glaucous-winged gulls (hybrids) nesting on Rat Island died (~3% of the local population), although gull chick mortality was high. Sixteen harbor seals in the immediate or nearby area stranded during the outbreak, and H5N1 HPAIV was detected in brain and/or lung tissue of five seals. These cases are the first known detections of HPAIV in a marine mammal on the Pacific coast of North America. Phylogenetic analyses support the occurrence of at least three independent avian-mammalian virus spillover events (tern or gull to harbor seal). Whole genome sequencing indicated that H5N1 HPAIV may have been introduced to Washington from Caspian terns in Oregon. Ongoing monitoring and surveillance for H5N1 HPAIV in the marine environment is necessary to understand the epidemiology of this virus, assess conservation impacts to susceptible species, and provide support for data-driven management and response actions.
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5 Conclusion
The global impact of H5N1 HPAIV clade 2.3.4.4b on wild birds and mammals is considerable based on raw mortality counts. However, few studies have accurately assessed the actual mortality and pattern of mortality across an entire outbreak or combined disease surveillance data with population monitoring (prior to the outbreak) to assess local colony and population impacts. Our investigation of the Rat Island outbreak employed comprehensive and multifaceted approaches that are uncommon in published studies of HPAI in free-ranging wildlife. In addition to the mortality event investigation, we also conducted population monitoring of Caspian terns at the onset of the outbreak, which allowed us to estimate total mortality. Using raw carcass counts collected nearly weekly during the outbreak, we were able to calculate population impacts of this outbreak on the terns. This was combined with diagnostic and genomic data confirming H5N1 HPAIV clade 2.3.4.4b infections in several hosts, including the first documentation of HPAI in a marine mammal in the Northeast Pacific. We document clear host susceptibility differences between breeding adult Caspian terns and gulls nesting at the same colony and in close proximity, with significant population level impacts for Caspian terns in the Pacific Flyway, yet very little impact to adult gulls. Finally, we found consistent patterns of the timing of H5N1 detection, the pattern of virus mutation, and the pattern of bird movement.
As comprehensive as our data are, we still lack a full understanding of these species’ immunological response(s) to IAV infections, especially H5N1 HPAIV, and how this affects susceptibility and disease outcomes in face of acute HPAI outbreaks and ongoing circulation of IAVs in the environment. This information gap and our findings highlight the importance of combining population monitoring, traditional and molecular epidemiological tools, and serologic surveillance for investigating wildlife morbidity and mortality events to better understand their impacts. We recommend expanding our wildlife health approach beyond mortality surveillance efforts (i.e., counting the dead) to also focus on population-level impacts and how environmental, behavioral, and immunological differences influence host susceptibility to disease, especially as H5N1 HPAI continues to devastate wildlife around the globe.
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https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2024.1483922/full
