#17,752
Hampered by highly sporadic surveillance and testing, the above map from the USDA showing H5N1 in mammals likely only represents a tiny fraction of the actual number of spillover events in the United States.
Many animals die unseen in remote swamps, forests, or deserts while others may recover, escaping detection (see Emerg. Microb. & Inf.: High Number of HPAI H5 Virus Infections & Antibodies in Wild Carnivores in the Netherlands , 2020–2022).
This week the EID Journal published a report from more than 2 dozen researchers across multiple states, which examines 67 terrestrial mammals (primarily foxes) infected with HPAI H5N1 clade 2.3.4.4b.
As we've seen often over the past couple of years (see Cell: The Neuropathogenesis of HPAI H5Nx Viruses in Mammalian Species Including Humans), neurological signs were frequently observed.
Note: We looked at this research 8 months ago before it was peer reviewed (see Preprint: Pathology Of HPAI H5N1 clade 2.3.4.4b in Wild Terrestrial Mammals in the United States in 2022).
Follow the link below to read the final version in its entirety.
Research
Highly Pathogenic Avian Influenza A(H5N1) Virus Clade 2.3.4.4b Infections in Wild Terrestrial Mammals, United States, 2022
Elizabeth J. Elsmo, Arno Wünschmann, Kimberlee B. Beckmen, Liam E. Broughton-Neiswanger, Elizabeth L. Buckles, Jayne Ellis, Scott D. Fitzgerald, Robert Gerlach, Shawna Hawkins, Hon S. Ip, Julia S. Lankton, Erin M. Lemley, Julianna B. Lenoch, Mary L. Killian, Kristina Lantz, Lindsey Long, Roger Maes, Marta Mainenti, Julie Melotti, Megan E. Moriarty, Shotaro Nakagun, Rachel M. Ruden, Valerie Shearn-Bochsler, Danielle Thompson, Mia K. Torchetti, Arnaud J. Van Wettere, Annabel G. Wise, and Ailam L. Lim
Abstract
We describe the pathology of natural infection with highly pathogenic avian influenza HPAI A(H5N1) virus of Eurasian lineage Goose/Guangdong clade 2.3.4.4b in 67 wild terrestrial mammals throughout the United States during April 1‒July 21, 2022. Affected mammals include 50 red foxes (Vulpes vulpes), 6 striped skunks (Mephitis mephitis), 4 raccoons (Procyon lotor), 2 bobcats (Lynx rufus), 2 Virginia opossums (Didelphis virginiana), 1 coyote (Canis latrans), 1 fisher (Pekania pennanti), and 1 gray fox (Urocyon cinereoargenteus).
Infected mammals showed primarily neurologic signs. Necrotizing meningoencephalitis, interstitial pneumonia, and myocardial necrosis were the most common lesions; however, species variations in lesion distribution were observed. Genotype analysis of sequences from 48 animals indicates that these cases represent spillover infections from wild birds.
Since October 2021, outbreaks of highly pathogenic avian influenza (HPAI) A(H5N1) virus belonging to A/Goose/Guangdong/1/1996 lineage H5 clade 2.3.4.4b have been reported throughout Europe (1). Transatlantic spread of HPAI H5N1 virus with genetic similarity to Eurasian lineages was detected in the United States in December 2021 and has subsequently spread throughout the continental United States in wild birds and domestic poultry (2‒6).
In addition to disease outbreaks in domestic poultry, currently circulating HPAI H5N1 virus is persisting in wild bird reservoirs, with multiple reports of spillover into and clinical infection in various mammal species in countries in Europe during 2021 (1,3,7). We report a case series on the pathology of natural infections with HPAI H5N1 virus in terrestrial wild mammals in the United States concurrent with high levels of circulating HPAI viruses in wild birds during the spring and summer of 2022.(SNIP)
Discussion
This case series highlights multiple detections of HPAI virus Eurasian lineage H5 clade 2.3.4.4b in wild terrestrial mammals in the United States. Our findings build on previous reports of natural infections with HPAI virus in red foxes from the Netherlands in 2021 (15) and add to the global list of species susceptible to H5N1 HPAI virus (16).
Red foxes are the most represented species in this report. Intrinsic factors related to exposure and infection risk could explain this finding, including opportunistic dietary preferences, likelihood of sharing environments with infected birds, abundance of immunologically naive animals present during the onset of the avian outbreak, and potentially increased susceptibility to infection in this species. Many of the red foxes were found in urban or periurban environments, and extrinsic factors, such as human interest in the highly visible animals, might have led to increased public reporting.
Raccoons, skunks, opossums, and coyotes are also generalist mesopredators frequently encountered in urban and periurban areas (17), and reasons why these species were less represented are unclear. Although serologic evidence of exposure to AIVs has been documented in many wild mammal species, few experiments have investigated the susceptibility of wild mammals to these viruses, and even fewer specifically to HPAI H5N1 virus (18). Additional studies on the susceptibility of mammal species to infection with the currently circulating strains of HPAI H5N1 virus might be warranted, especially in light of the unprecedented reassortment of the Newfoundland-like virus with North American wild bird origin influenza viruses (3).
Neurologic signs were the primary clinical observation in this report, consistent with reports of HPAI H5N1 infections in mammals in Europe (7,15) and in infected birds of prey (19,20). Although widespread lesions and viral detection from multiple tissues are consistent with systemic infections in those mammals, necrotizing and nonsuppurative meningoencephalitis and acute interstitial pneumonia were the primary microscopic lesions, followed by myocardial necrosis, hepatic necrosis, and lymphoid depletion. Those findings are also consistent with lesion distribution in previous reports of natural and experimental HPAI virus infections in mammals (7,15,21,22) and raptors (19,20,23).
(SNIP)
In summary, we demonstrate that multiple North America wild terrestrial mammal species are susceptible to natural infection with HPAI H5N1 virus of Eurasian lineage goose/Guangdong H5 clade 2.3.4.4b, probably by ingestion of infected wild birds. Neurologic signs were the primary clinical manifestation, and HPAI virus infection warrants consideration as a differential diagnosis along with more common causes of neurologic disease in wild mammals. Given the ongoing nature of the HPAI virus outbreak and the detection of genetic substitutions concerning for mammalian adaptation, surveillance for HPAI virus in wild mammals would contribute to a better understanding of the distribution and evolution of these viruses in free-ranging wildlife.
Dr. Elsmo is an assistant professor of clinical diagnostic veterinary pathology at the Wisconsin Veterinary Diagnostic Laboratory and the University of Wisconsin School of Veterinary Medicine, Madison, Wisconsin. Her primary research interest is infectious diseases, particularly those at the wildlife, domestic animal, and human interface.
