Concurrent Avian Influenza Subtypes Detected in UK Wildlife: A Novel Outbreak
Avian influenza, a highly contagious viral disease, continues to pose a significant threat to both wild bird populations and poultry industries globally. Since late 2020, Great Britain (GB) has experienced recurring outbreaks of highly pathogenic avian influenza (HPAI) viruses, primarily of the H5N1 subtype. While H5N1 has been dominant, limited detections of H5N5 have also been observed. These viruses have triggered widespread mortality events affecting a diverse range of avian species, and increasingly, various mammalian populations, including both land-based and marine animals.
Recent investigations into a mortality event along the Norfolk coastline in eastern England revealed a notably concerning development: the simultaneous presence of two distinct HPAI subtypes within the same location and avian population. Pathological analysis of deceased birds uncovered H5N1 HPAIV in five Great Black-backed Gulls ( Larus marinus) and one Northern Fulmar (Fulmarus glacialis). Strikingly, the same event also yielded positive results for H5N5 HPAIV in a larger group – seventeen Great black-backed Gulls, one Herring Gull (Larus argentatus), one Atlantic Puffin (Fratercula arctica), and another Northern Fulmar.
The outbreak’s impact extended beyond avian species. Researchers also detected H5N5 in seventeen Gray Seal carcasses (Halichoerus grypus) found in close proximity to the bird mortality site. This marks the first documented instance of a mass detection of H5N5 HPAIV in mammals within Great Britain, raising concerns about potential cross-species transmission and the evolving dynamics of the virus.
Genetic analysis revealed key differences between the detected viruses. The H5N1 HPAIV isolated from the infected bird belonged to genotype DI.2,aligning with other recent H5N1 detections in GB wild birds and poultry. However, all H5N5 HPAIVs – those found in both birds and seals – were genotype I, characterized by a 22-amino acid deletion in the neuraminidase (NA) stalk and a 627K polymorphism in the PB2 protein. These genetic markers suggest a distinct evolutionary pathway for the H5N5 viruses circulating in this outbreak.The co-occurrence of H5N1 and H5N5 at the same location is unprecedented in GB, challenging previous understandings of the spatial distribution of these subtypes. While temporal overlaps in outbreaks have been noted, they have typically occurred in separate geographic areas. The current findings suggest a more complex interplay between the viruses, possibly facilitated by factors such as migratory bird movements, environmental conditions, or interactions between avian and marine mammal populations.Further research is crucial to elucidate the mechanisms driving this co-infection and to assess the potential for future outbreaks involving multiple subtypes. As of mid-2024, global HPAI outbreaks have led to the culling of over 50 million poultry birds worldwide, highlighting the ongoing economic and ecological consequences of this disease.