Characterization of H5N6 highly pathogenic avian influenza viruses isolated from wild and captive birds in the winter season of 2016–2017 in Northern Japan

Abstract

On 15 November 2016, a black swan that had died in a zoo in Akita prefecture, northern Japan, was strongly suspected to have highly pathogenic avian influenza (HPAI); an HPAI virus (HPAIV) belonging to the H5N6 subtype was isolated from specimens taken from the bird. After the initial report, 230 cases of HPAI caused by H5N6 viruses from wild birds, captive birds, and domestic poultry farms were reported throughout the country during the winter season. In the present study, 66 H5N6 HPAIVs isolated from northern Japan were further characterized. Phylogenetic analysis of the hemagglutinin gene showed that the H5N6 viruses isolated in northern Japan clustered into Group C of Clade 2.3.4.4 together with other isolates collected in Japan, Korea and Taiwan during the winter season of 2016-2017. The antigenicity of the Japanese H5N6 isolate differed slightly from that of HPAIVs isolated previously in Japan and China. The virus exhibited high pathogenicity and a high replication capacity in chickens, whereas virus growth was slightly lower in ducks compared with that of an H5N8 HPAIV isolate collected in Japan in 2014. Comprehensive analyses of Japanese isolates, including those from central, western, and southern Japan, as well as rapid publication of this information are essential for facilitating greater control of HPAIVs.

Phylogenetic variations of highly pathogenic H5N6 avian influenza viruses isolated from wild birds in the Izumi plain, Japan, during the 2016–17 winter season

“…In the constructed phylogenetic trees based on the H5 HA (Supporting information Figure S1A), N6 NA (Supporting information Figure S1B), NP (Supporting information Figure S2A), and M (Supporting information Figure S2B) genes, the 33 H5N6 HPAIV isolates formed a single cluster with the other contemporary H5N6 HPAIV isolates. Consistent with previous findings (Hiono et al., ; Takemae et al., ), our results suggested no phylogenetic variations in the four gene segments of all H5N6 HPAIVs isolated globally during the 2016–2017 winter season.…”

“…Previously reported H5N6 HPAIV isolates during the 2016–2017 winter season were divided into six genotypes C1–C6, based on four and two phylogenetic variations in the PA and NS gene segments respectively (Figure c,d) (Hiono et al., ; Lee et al., ; Takemae et al., ). Phylogenetic analyses identified variations in the PB2 (Figure a) and PB1 (Figure b) gene segments and two and one additional phylogenetic variations in the PA (Figure c) and NS (Figure d) gene segments, respectively, among H5N6 HPAIV isolates during the same season.…”

“…Genome sequencing of the early Korean isolates revealed that the H5N6 HPAIVs can be classified into five genotypes (C1–C5) that harboured four (PA‐I to ‐IV) and two (NS‐I and ‐II) phylogenetic variations in the PA and NS gene segments, respectively (Lee et al., ). Subsequently, all H5N6 HPAIVs previously isolated in Japan, including two early isolates from the Izumi plain, were classified into the four known genotypes (C1, C2, C4, and C5) (Hiono et al., ; Okamatsu et al., ; Takemae et al., ), except for one isolate A/chicken/Miyazaki/2‐1T/2017(H5N6) whose PA gene segment was phylogenetically distinct from those of the remaining contemporary H5N6 HPAIV isolates. Therefore, A/chicken/Miyazaki/2‐1T/2017(H5N6) was classified under the genotype C6 (Takemae et al., ).…”

Comparative pathogenicity of H5N6 subtype highly pathogenic avian influenza viruses in chicken, Pekin duck and Muscovy duck

“…Several animal experiments have demonstrated that even among the H5 HPAIVs belonging to clade 2.3.4.4, their pathogenicity in chickens as well as the susceptibility of other avian hosts to them differ when examined in vivo (Hiono et al., ; Kanehira et al., ; Okamatsu et al., ; Pantin‐Jackwood et al., ; Song et al., ; Tanikawa et al., and Usui et al., ). The 50% chicken lethal dose (CLD 50 ) values and Mean death time (MDT) differed considerably among HPAIVs belonging to clade 2.3.4.4 that were isolated in 2014 in Japan, Korea and the US (Kanehira et al., ; Pantin‐Jackwood et al., ; Song et al., ; Tanikawa et al., ).…”

Outbreaks of highly pathogenic avian influenza in zoo birds caused by HA clade 2.3.4.4 H5N6 subtype viruses in Japan in winter 2016

“…Ten waterfowl, including three black swans (1–3), four cackling geese (1–4), two mallards ( Anas platyrhynchos ) (1 and 2) and a wigeon ( Anas penelope ) housed in two small ponds in the zoo, Kocho pond and Kodai pond, died or were euthanized after HPAIV infection between 29 November and 17 December 2016 (Table ). To confirm HPAIV infection, tracheal and cloacal swabs collected from all dead birds at both zoos were sent to the Avian Zoonosis Research Center of Tottori University and tested for virus isolation, with the exception of virus isolation tests of three black swans at Omoriyama Zoo, which were performed at a diagnostic laboratory at Hokkaido University (Hiono et al, ).…”