Research Note: Comparative evaluation of pathogenicity in SPF chicken between different subgroups of H5N6 high pathogenicity avian influenza viruses

Since 2014, periodic outbreaks of high pathogenicity avian influenza (HPAI) caused by clade 2.3.4.4 H5 HPAI virus (HPAIV) have resulted in huge economic losses in the Korean poultry industry. During the winter season of 2016-2017, clade 2.3.4.4e H5N6 HPAIVs classified into 5 subgroups (C1-5) were introduced into South Korea. Interestingly, it was revealed that the subgroup C2 and C4 viruses were predominantly distributed throughout the country, whereas detection of the subgroup C3 viruses was confined in a specific local region. In the present study, we conducted comparative evaluation of the pathogenicity of viruses belonging to subgroups C2 and C3 (H15 and HN1 strains) in specific pathogen-free (SPF) chickens, and further compared them with previously determined pathogenicity of subgroup C4 (ES2 strain) virus. The HN1 strain showed lower viral replication in tissues, less transmissibility, and higher mean chicken lethal dose than the H15 and ES2 strains in SPF chickens. Considering that the HN1 strain has a different NS gene segment from the H15 and ES2 strains, the reassortment of the NS gene segment likely affects their infectivity and transmissibility in chickens. These findings emphasize the importance of monitoring the genetic characteristics and pathogenic features of HPAIVs to effectively control their outbreaks in the field.

Experimental Infection of Chickens with H5N8 High Pathogenicity Avian Influenza Viruses Isolated in Japan in the Winter of 2020-2021

During the winter of 2020-2021, numerous outbreaks of high pathogenicity avian influenza (HPAI) were caused by viruses of the subtype H5N8 in poultry over a wide region in Japan. The virus can be divided into five genotypes-E1, E2, E3, E5, and E7. The major genotype responsible for the outbreaks was E3, followed by E2. To investigate the cause of these outbreaks, we experimentally infected chickens with five representative strains of each genotype. We found that the 50% chicken infectious dose differed by up to 75 times among the five strains, and the titer of the E3 strains (102.75 50% egg infectious dose (EID50)) was the lowest, followed by that of the E2 strains (103.50 EID50). In viral transmission experiments, in addition to the E3 and E2 strains, the E5 strain was transmitted to naïve chickens with high efficiency (>80%), whereas the other strains had low efficiencies (<20%). We observed a clear difference in the virological characteristics among the five strains isolated in the same season. The higher infectivity of the E3 and E2 viruses in chickens may have caused the large number of HPAI outbreaks in Japan during this season.

Detection of H5N1 High Pathogenicity Avian Influenza Viruses in Four Raptors and Two Geese in Japan in the Fall of 2022

In the fall of 2022, high pathogenicity avian influenza viruses (HPAIVs) were detected from raptors and geese in Japan, a month earlier than in past years, indicating a shift in detection patterns. In this study, we conducted a phylogenetic analysis on H5N1 HPAIVs detected from six wild birds during the 2022/2023 season to determine their genetic origins. Our findings revealed that these HPAIVs belong to the G2 group within clade 2.3.4.4b, with all isolates classified into three subgroups: G2b, G2d, and G2c. The genetic background of the G2b virus (a peregrine falcon-derived strain) and G2d viruses (two raptors and two geese-derived strains) were the same as those detected in Japan in the 2021/2022 season. Since no HPAI cases were reported in Japan during the summer of 2022, it is probable that migratory birds reintroduced the G2b and G2d viruses. Conversely, the G2c virus (a raptor-derived strain) was first recognized in Japan in the fall of 2022. This strain might share a common ancestor with HPAIVs from Asia and West Siberia observed in the 2021/2022 season. The early migration of waterfowl to Japan in the fall of 2022 could have facilitated the early invasion of HPAIVs.

Newly emerged genotypes of highly pathogenic H5N8 avian influenza viruses in Kagoshima prefecture, Japan during winter 2020/21

During the 2020/21 winter season, 29 and 10 H5N8 high pathogenicity avian influenza viruses (HPAIVs) were isolated from environmental water and wild birds, respectively, in Kagoshima prefecture, Japan. Furthermore, seven subtypes of low pathogenicity avian influenza viruses (LPAIVs) were also isolated; H1N1, H2N9, H3N2, H3N6, H3N8, H4N6, and H6N6 subtypes. While the H5 hemagglutinin (HA) genes of the G1 cluster were isolated throughout the winter season, those of the G2 cluster were also detected in late winter, suggesting that H5 HPAIVs possessing H5 HA genes from the two different clusters were individually introduced into Kagoshima prefecture. Intriguingly, genetic constellations revealed that the H5N8 HPAIVs could be classified into six genotypes, including four previously reported genotypes (E1, E2, E3, and E7), and two new genotypes (tentatively named E8 and E9). The PB1 and PA gene segments of genotypes E8 and E9 shared high similarity with those of LPAIVs, whereas the remaining gene segments were close to those of genotype E1. Furthermore, LPAIVs whose PA gene segment was close to that of genotype E9 were isolated from the environmental water. Overall, we revealed that various HPAIV genotypes circulated in Kagoshima prefecture during the 2020/21 winter season. This study highlights the importance of monitoring both HPAIV and LPAIV to better understand AIV ecology in migratory waterfowl populations.

Different Infectivity and Transmissibility of H5N8 and H5N1 High Pathogenicity Avian Influenza Viruses Isolated from Chickens in Japan in the 2021/2022 Season

H5N8 and H5N1 high pathogenicity avian influenza viruses (HPAIVs) caused outbreaks in poultry farms in Japan from November 2021 to May 2022. Hemagglutinin genes of these viruses belong to clade 2.3.4.4B and can be divided phylogenetically into the following groups: 20A, 20E, and 21E. In this study, we compared the infectivity and transmissibility of HPAIVs from three groups of chickens. Representative strains from 20A, 20E, and 21E groups are A/chicken/Akita/7C/2021(H5N8)(Akita7C), A/chicken/Kagoshima/21A6T/2021(H5N1)(Kagoshima6T), and A/chicken/Iwate/21A7T/2022(H5N1)(Iwate7T), respectively. Fifty percent lethal dose of Akita7C in chickens (10^3.83 fifty percent egg infectious dose (EID50)) was up to seven times lower than those of Kagoshima6T and Iwate7T (10^4.50 and 10^4.68 EID_50, respectively). Mean death times for Akita7C- and Kagoshima6T-infected chickens (3.45 and 3.30 days, respectively) were at least a day longer than that of Iwate7T (2.20 days). Viral titers of the trachea and cloaca of Iwate7T-infected chicken were the highest detected. The transmission rate of the Akita7C strain (100%) was markedly higher than those of the two strains (<50%). These data suggest that the infectivity and transmissibility of the Akita7C strain (H5N8) in chickens are higher than those of H5N1 viruses, providing fundamental information needed for formulating effective prevention and control strategies for HPAI outbreaks.

Genetically Diverse Highly Pathogenic Avian Influenza A(H5N1/H5N8) Viruses among Wild Waterfowl and Domestic Poultry, Japan, 2021

Genetic analyses of highly pathogenic avian influenza H5 subtype viruses isolated from the Izumi Plain, Japan, revealed cocirculation of 2 genetic groups of clade 2.3.4.4b viruses among migratory waterfowl. Our findings demonstrate that both continuous surveillance and timely information sharing of avian influenza viruses are valuable for rapid risk assessment.

Emergence of clade 2.3.4.4b novel reassortant H5N1 High Pathogenicity avian influenza virus in South Korea during late 2021

High pathogenicity H5N1 avian influenza viruses pose a threat to both animal and human health worldwide. In late 2020, outbreaks of H5 high pathogenicity avian influenza viruses belonging to clade 2.3.4.4b emerged in Europe, following on from outbreaks in East Asia in earlier years. However, very recent studies show that clade 2.3.4.4b H5N1, rather than 2.3.4.4b H5N8, has become predominant in wild birds and has infected poultry in several countries. In this study, we describe isolation of a novel H5N1 virus from a captured mandarin duck in South Korea, and another H5N1 virus from a quail farm. We performed genetic analysis of these two viruses to identify their origin and to determine their relationship with the clade 2.3.4.4b H5N1 viruses currently circulating in Europe. Based on our results, it is presumed that the novel H5N1 virus isolated in Korea originated from an unknown reassortant between clade 2.3.4.4b H5N8 viruses circulating from 2020 and other Eurasian viruses, with additional reassortment of genes and point mutations that discriminate them from the recently reported H5N1 virus in Europe. This article is protected by copyright. All rights reserved.