Detection of Highly Pathogenic Avian Influenza Virus H5N1 Clade 2.3.4.4b in Great Skuas: A Species of Conservation Concern in Great Britain

Abstract

The UK and Europe have seen successive outbreaks of highly pathogenic avian influenza across the 2020/21 and 2021/22 autumn/winter seasons. Understanding both the epidemiology and transmission of these viruses in different species is critical to aid mitigating measures where outbreaks cause extensive mortalities in both land- and waterfowl. Infection of different species can result in mild or asymptomatic outcomes, or acute infections that result in high morbidity and mortality levels. Definition of disease outcome in different species is of great importance to understanding the role different species play in the maintenance and transmission of these pathogens. Further, the infection of species that have conservation value is also important to recognise and characterise to understand the impact on what might be limited wild populations. Highly pathogenic avian influenza virus H5N1 clade 2.3.4.4b has been detected in great skuas (Stercorarius skua) across different colonies on islands off the shore of Scotland, Great Britain during summer 2021. A large number of great skuas were observed as developing severe clinical disease and dying during the epizootic and mortalities were estimated to be high where monitored. Of eight skuas submitted for post-mortem examination, seven were confirmed as being infected with this virus using a range of diagnostic assays. Here we overview the outbreak event that occurred in this species, listed as species of conservation concern in Great Britain and outline the importance of this finding with respect to virus transmission and maintenance.

Keywords: H5N1; conserved species; highly pathogenic avian influenza; outbreak; transmission.

Figure 1

Geographical distribution of great skua carcasses and timeline of detection. The distribution of observed deaths is shown on the map for each island. Cases are coloured according to time of observation as denoted in the key. The size of circle is proportional to the number of cases with larger circles denoting a greater number of observed mortalities as per the key. Positive cases are also noted or each island.

Figure 2

Microscopic findings of great skua infected with HPAIV H5N8. (a) Severe pancreatic necrosis with abundant virus antigens; (b) Mild non-suppurative meningoencephalitis with confluent viral immunopositive immunolabelling; (c) Rare myocardial necrosis associated with scattered virus antigens; (d) Moderate adrenal necrosis with confluent virus antigen labelling; (e) Rare multifocal hepatic necrosis with scattered viral immunolabelling; (f) A focus of glandular necrosis of the proventriculus and scattered immunolabelling within the submucosa. Region of interest within IHC images outlined by dotted line box corresponds to H&E insets. Immunohistochemical images were taken at 100× magnification. Histological images were taken at 400× magnification for a to e but 200× for the proventriculus.