In a study recently published within the journal Researchers in Alaska, United States of America (USA), reported a natural infection with the highly pathogenic avian influenza virus (HPAI) A(H5N1) in a young, wild polar bear found dead in Alaska in 2023. They emphasized the importance of continuous monitoring of wildlife health by the general public and hunters within the Arctic.
background
The HPAI virus A(H5N1) of clade 2.3.4.4b was first detected in Europe in October 2020 and has since incessantly infected various mammal species worldwide. In North America, natural avian influenza infections have been observed in several bear species, including Asian black bears, American black bears, grizzly bears, and Kodiak brown bears. Animals in captivity, including sloth bears, Asian black bears, and giant pandas, have been reported to have develop into infected with other influenza A(H1N1) viruses. As well as, antibodies against influenza subtypes H3 and H6 indicate previous natural exposures to avian influenza viruses. Particularly, Seroconversion was observed in polar bears within the Barents Sea and in brown bears in Alaska, but not in polar bears within the southern Beaufort Sea.
Interestingly, genome evaluation of influenza viruses in Alaska has revealed each non-reassorted and reassorted strains. HPAI virus genotype A3 was likely introduced into Alaska via the East Asia-Australia Flyway in November 2021. Since then, it has been detected in various wild birds, including California condors in Arizona, and mammals similar to red foxes, fisher martens, martens, raccoons, and brown bears along the Pacific Flyway.
Polar bears () are considered a threatened species under the US Endangered Species Act. Understanding their health threats is critical for species conservation and developing effective management strategies. In the current study, researchers report the case of a male polar bear who was naturally infected with the HPAI virus H5N1 and succumbed to the infection.
In regards to the study
The North Slope Borough Department of Wildlife Management (NSB DWM) in Alaska conducts research into wildlife health and maintains programs to watch community hunting of marine mammals, including polar bears. The Alaska Office of the State Veterinarian oversees wildlife surveillance for reportable infectious diseases. After HPAI H5N1 was detected in birds of prey and a red fox in April 2022, the Office of the State Veterinarian began collaborating with the NSB DWM on surveillance testing for avian influenza in birds and other wildlife.
Local residents reported finding a dead polar bear near Point Barrow, Alaska, in August 2023. An autopsy was performed. The bear was found to be a 120 cm long male cub in moderate to advanced decomposition. After macroscopic examination, tissue samples were collected and stuck in 10% buffered formalin for histopathological examination. Swab samples were also collected and stored at −50 °C. They were processed for routine histopathological examination with eosin and hematoxylin staining. The swab samples were tested for the influenza virus matrix gene using polymerase chain response (PCR). Immunohistochemistry was performed using a polyclonal antibody against influenza A virus. As well as, molecular confirmation and characterization of the virus genome were performed.
Results and discussion
Macroscopic examination revealed liver and lung congestion, ulcerative skin lesions, hematoma, brain swelling and congestion, and an empty stomach. The most important histopathological findings were granulocytic and mononuclear meningoencephalitis with microgliosis, neuronophagia, vasculitis, neuronal necrosis, and parenchymal thinning. As well as, the researchers noted focal lipid pneumonia, pulmonary edema, and multifocal ulcerative dermatitis. Swab samples were negative for the influenza virus matrix gene. Despite negative PCR tests, immunohistochemistry detected influenza A virus. antigen in neurons and microglial cells. Molecular evaluation identified HPAI virus genotype A3, a Eurasian influenza virus. The virus was first detected in Alaska in April 2022 and was essentially the most incessantly detected genotype within the region during August–December 2023. Complete genome sequences of the virus that infects polar bears have been deposited in GenBank and GISAID (short for Global Initiative on Sharing All Influenza Data).
Diploma
In summary, the invention of HPAI H5N1 in a polar bear indicates that the virus can jump to different mammal species. This highlights the necessity for vigilant surveillance of wildlife health (by each community and hunters) to detect emerging pathogens early. The successful discovery of the virus through collaboration between wildlife management departments and government veterinarians highlights the importance of integrated surveillance systems in monitoring and responding to wildlife health issues. Because polar bears and other wildlife are essential to the livelihoods and food security of indigenous communities within the Arctic, the invention of HPAI H5N1 indicates potential zoonotic risks. This requires strategies to mitigate impacts on traditional food sources and protect public health. The findings provide worthwhile data on the distribution and impact of HPAI H5N1 within the Arctic and contribute to the broader scientific understanding of influenza virus ecology and interspecies transmission dynamics.
