Avian influenza virus (AIV) is classified as high or low pathogenicity AIV (HPAIV/LPAIV) based on intravenous pathogenicity in chickens and/or the presence or absence of multiple basic residues at the heamagglutinin (HA) cleavage site (CS). Since 2014, Europe has experienced waves of incursions of H5Nx HPAIV. Between November 2020 and March 2021, these included HPAIV H5N8, with sporadic of H5N1 and H5N5 (all clade 2.3.4.4b), detected in more than 300 "found dead" wild birds submitted through a passive surveillance programme in the United Kingdom. Currently, H5Nx HPAIV detection relies on identification of AIV RNA and H5 subtyping using real-time reverse transcription PCR (rRT-PCR) assays. The pathotype is subsequently determined by Sanger sequencing of the HA CS. Here, we report the validation and application of a rapid, more cost-effective HP H5-detection rRT-PCR assay. The HP H5 rRT-PCR assay specifically, sensitively and reproducibly detected RNA from contemporary clade 2.3.4.4b H5 HPAIVs with comparable sensitivity to the diagnostic H5-specific rRT-PCR; LPAIV H5 RNA and non-AIV RNA were not detected. On material from "found-dead" wild birds, and for statutory disease diagnosis on poultry, the HP H5 rRT-PCR results provided 100% discrimination when compared to conventional CS sequencing, significantly reducing time-to-pathotype determination and cost, enhancing the diagnostic workflow.

Genetic sequences of a highly pathogenic avian influenza (H5N8) virus in England have high homology to those detected in mainland Europe and Asia during 2014. Genetic characterization suggests this virus is an avian-adapted virus without specific affinity for zoonoses. Spatio-temporal detections of H5N8 imply a role for wild birds in virus spread.

Widespread H5N8 highly pathogenic avian influenza virus (HPAIV; clade 2.3.4.4b) infections occurred in wild birds and poultry across Europe during winter 2016–17. Four different doses of H5N8 HPAIV (A/wigeon/Wales/052833/2016 [wg-Wal-16]) were used to infect 23 Pekin ducks divided into four separate pens, with three contact turkeys introduced for cohousing per pen at 1 day postinfection (dpi). All doses resulted in successful duck infection, with four sporadic mortalities recorded among the 23 (17%) infected ducks, which appeared unrelated to the dose. The ducks transmitted wg-Wal-16 efficiently to the contact turkeys; all 12 (100%) turkeys died. Systemic viral dissemination was detected in multiple organs in two duck mortalities, with limited viral dissemination in another duck, which died after resolution of shedding. Systemic viral tropism was observed in two of the turkeys. The study demonstrated the utility of Pekin ducks as surrogates of infected waterfowl to model the wild bird/gallinaceous poultry interface for introduction of H5N8 HPAIV into terrestrial poultry, where contact turkeys served as a susceptible host. Detection of H5N8-specific antibody up to 58 dpi assured the value of serologic surveillance in farmed ducks by hemagglutination inhibition and anti-nucleoprotein ELISAs.

Highly-pathogenic avian influenza virus (HPAIV) H5N6 (clade 2.3.4.4b) incurred into Europe in late 2017 and was predominantly detected in wild birds, with very few terrestrial poultry cases. Pekin ducks directly-infected with a UK virus (H5N6-2017) were donors of infection to investigate contact transmission to three recipient species: Ducks, chickens and turkeys. H5N6-2017 transmission to ducks was 100% efficient, but transmission to in-contact galliforme species was infrequent and unpredictable, thereby reflecting the European 2017-2018 H5N6 epidemiology. Although only two of 28 (7%) infected ducks died, the six turkeys and one chicken which became infected all died and displayed systemic H5N6-2017 dissemination, while pathogenesis in ducks was generally milder. Analysis of H5N6-2017 progeny in the contacts revealed no emergent polymorphisms in an infected duck, but the galliforme species included changes in the polymerase (PB2 A199T, PA D347A), matrix (M1 T218A) and neuraminidase genes (T88I). H5N6-2017 environmental contamination was associated with duck shedding.

The China-origin H7N9 low pathogenicity avian influenza virus (LPAIV) emerged as a zoonotic threat in 2013 where it continues to circulate in live poultry markets. Absence of overt clinical signs in poultry is a typical LPAIV infection outcome, and has contributed to its insidious maintenance in China. This study is the first description of H7N9 LPAIV (A/Anhui/1/13) infection in turkeys, with efficient transmission to two additional rounds of introduced contact turkeys which all became infected during cohousing. Surprisingly, mortality was observed in six of eight (75%) second-round contact turkeys which is unusual for LPAIV infection, with unexpected systemic dissemination to many organs beyond the respiratory and enteric tracts, but interestingly no accompanying mutation to highly pathogenic AIV. The intravenous pathogenicity index score for a turkey-derived isolate (0.39) affirmed the LPAIV phenotype. However, the amino acid change L235Q in the haemagglutinin gene occurred in directly-infected turkeys and transmitted to the contacts, including those that died and the two which resolved infection to survive to the end of the study. This polymorphism was indicative of a reversion from mammalian to avian adaptation for the H7N9 virus. This study underlined a new risk to poultry in the event of H7N9 spread beyond China.