First Outbreak of an H5N8 Highly Pathogenic Avian Influenza Virus on a Chicken Farm in Japan in 2020

Abstract

On 5 November 2020, a confirmed outbreak due to an H5N8 highly pathogenic avian influenza virus (HPAIV) occurred at an egg-hen farm in Kagawa prefecture (western Japan). This virus, A/chicken/Kagawa/11C/2020 (Kagawa11C2020), was the first HPAI poultry isolate in Japan in 2020 and had multiple basic amino acids—a motif conferring high pathogenicity to chickens—at the hemagglutinin cleavage site. Mortality of chickens was 100% through intravenous inoculation tests performed according to World Organization for Animal Health criteria. Phylogenetic analysis showed that the hemagglutinin of Kagawa11C2020 belongs to clade 2.3.4.4B of the H5 Goose/Guangdong lineage and clusters with H5N8 HPAIVs isolated from wild bird feces collected in Hokkaido (Japan) and Korea in October 2020. These H5N8 HPAIVs are closely related to H5N8 HPAIVs isolated in European countries during the winter of 2019–2020. Intranasal inoculation of chickens with 106 fifty-percent egg infectious doses of Kagawa11C2020 revealed that the 50% chicken lethal dose was 104.63 and the mean time to death was 134.4 h. All infected chickens demonstrated viral shedding beginning on 2 dpi—before clinical signs were observed. These results suggest that affected chickens could transmit Kagawa11C2020 to surrounding chickens in the absence of clinical signs for several days before they died.

Pathogenicity of H5N8 High Pathogenicity Avian Influenza Virus in Chickens and Ducks from South Korea in 2020–2021

“…The genetic similarity between HPAI viruses may correlate with similar pathogenicity in chickens. The pathogenicity of H5N8/2020 isolated in Japan and reported in a recent study, which has a cLD 50 of 10 4.63 EID 50 and MDT of 5.6 days, is similar to our findings concerning H242/20(H5N8) in SPF chickens [ 24 ].…”

“…H242/20(H5N8) in this study is genetically similar to these European viruses detected in 2019–2020 [ 15 ]. In addition, H242/20(H5N8) shows genetic similarity with H5N8 HPAI viruses isolated in Japan during a recent outbreak in 2020–2021 [ 24 , 25 , 26 ]. The genetic similarity between HPAI viruses may correlate with similar pathogenicity in chickens.…”

Susceptibility of Common Family Anatidae Bird Species to Clade 2.3.4.4e H5N6 High Pathogenicity Avian Influenza Virus: An Experimental Infection Study

“…These results indicate that wild duck are involved in transboundary dissemination of HPAIV. In island countries such as Japan, increases and decreases in the seroprevalence in migratory ducks is probably correlated with the occurence of HPAI every few years [34]. The challenge virus was recovered from two cELISA-positive juvenile mallards, suggesting that heterologous antibody is less likely to inhibit propagation of HPAIV in Anatidae.…”

Dynamics of invasion and dissemination of H5N6 highly pathogenic avian influenza viruses in 2016–2017 winter in Japan

“…While these reports have collated important information from each specific HPAI situation, a comprehensive study including geographical and time course validations is required to maximize the understanding of the 2016-2017 experience, to better respond to expected future cases. HPAI occurred in Japan in 2017-2018 [23,37] and 2020-2021 [12,15,30] by clade 2.3.4.4b H5N6 and H5N8 viruses, respectively, and is likely to continue. In the present study, 58 HPAIVs isolated at Tottori University add to the phylogenetic analyses together with other reported strains to understand overall HPAI circumstances in 2016-17 in Japan.…”