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High pathogenicity avian influenza (HPAI) viruses of clade 2.3.4.4 H5Nx have been circulating in poultry and wild birds worldwide since 2014. In South Korea, after the first clade 2.3.4.4b H5N1 HPAI viruses were isolated from wild birds in October 2021, additional HPAIV outbreaks occurred in poultry farms until April 2022. In this study, we genetically characterized clade 2.3.4.4b H5N1 HPAIV isolates in 2021–2022 and examined the pathogenicity and transmissibility of A/mandarin duck/Korea/WA585/2021 (H5N1) (WA585/21) in chickens and ducks. Clade 2.3.4.4b H5N1 HPAI viruses caused 47 outbreaks in poultry farms and were also detected in multiple wild birds. Phylogenetic analysis of HA and NA genes indicated that Korean H5N1 HPAI isolates were closely related to Eurasian viruses isolated in 2021–2022. Four distinct genotypes of H5N1 HPAI viruses were identified in poultry, and the majority were also found in wild birds. WA585/21 inoculated chickens showed virulent pathogenicity with high mortality and transmission. Meanwhile, ducks infected with the virus showed no mortality but exhibited high rates of transmission and longer viral shedding than chickens, suggesting that they may play an important role as silent carriers. In conclusion, consideration of both genetic and pathogenic traits of H5N1 HPAI viruses is required for effective viral control. [ABSTRACT FROM AUTHOR]

Since October 2020, H5N1 clade 2.3.4.4b high pathogenicity avian influenza (HPAI) viruses have spread to many countries. Although these viruses evolved from Eurasian ancestors, reassortant with other LPAI viruses has generated various genotypes. Here, we identified three H5N1 HPAI viruses belonging to clade 2.3.4.4b; these viruses were isolated from mandarin duck, common teal, and domestic breeder ducks in October 2022 during an avian influenza (AI) active surveillance program. Two of the H5N1 viruses (MD/WA496 and BD/H493) have been found sporadically in China, Russia, and Korea. It is presumed that two viruses with a similar gene constellation isolated in Russia, China, and Korea were introduced into the breeding area during the spring migration, and were introduced newly to Korea during the autumn migration. Due to international bird migration, the other virus (CT/WA537) is most similar (99.3–99.8%) to a virus detected in North Dakota, USA in April 2022. These results suggest that H5N1 viruses with at least two genotypes were introduced at the same time into Korea during the autumn of 2022, and that they originated from Eurasian breeding grounds and North America. Thus, multiple 2.3.4.4b H5N1 viruses were introduced into Korea during the autumn season of 2022. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Human infection by avian‐origin subtype H10 influenza viruses has raised concerns about the pandemic potential of these microbes. H10 subtype low pathogenic avian influenza viruses (LPAIVs) have been isolated from wild birds and poultry worldwide. Here, we isolated 36 H10 LPAIVs from wild bird habitats (a mean annual rate of 3.8% of all avian influenza virus isolations) from January 2010 to April 2019 through a nationwide active surveillance program for avian influenza viruses (AIVs). Phylogenetic analysis revealed that the haemagglutinin (HA) gene of H10 isolates formed eight distinct genetic subgroups (HA‐A–H). Unlike other Eurasian‐origin subgroups, the HA‐H subgroup belonged to the North American lineage. Gene‐constellation analysis revealed that 24 H10 LPAIVs constituted ≥18 distinct genotypes, representing high levels of genetic diversity. An intravenous pathogenicity index (IVPI) experiment showed that the pathogenicity of representative strains of the HA‐B, E and G subgroups possessing an IVPI score >1.2 was associated with replication capacity in the chicken kidney in the absence of trypsin. Intranasal inoculation experiments showed that a representative strain of the HA‐D subgroup replicated and transmitted in chickens without clinical signs. Subclinical virus shedding in chickens may contribute to its silent spread among the poultry population. Moreover, six representative viruses replicated in the lungs of mice without prior adaptation and a representative strain of the HA‐C subgroup caused 40% mortality, with severe body weight loss. These findings highlight the importance of intensive surveillance of wild bird habitats, poultry farms and the animal–human interface, along with appropriate risk assessment of isolated viruses. [ABSTRACT FROM AUTHOR]

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We report the identification of novel highly pathogenic avian influenza viruses of subtype H5N6, clade 2.3.4.4, that presumably originated from China. In addition, reassortant strains with Eurasian lineage low pathogenic avian influenza viruses were isolated in wild birds and poultry in South Korea. The emergence of these novel H5N6 viruses and their circulation among bird populations are of great concern because of the potential for virus dissemination with intercontinental wild bird migration. [ABSTRACT FROM AUTHOR]

The past two decades have seen the emergence of highly pathogenic avian influenza (HPAI) infections that are characterized as extremely contagious, with a high fatality rate in chickens, and humans; this has sparked considerable concerns for global health. Generally, the new variant of the HPAI virus crossed into various countries through wild bird migration, and persisted in the local environment through the interactions between wild and farmed birds. Nevertheless, no studies have found informative cases associated with connecting local persistence and long-range dispersal. During the 2016–2017 HPAI H5N6 epidemic in South Korea, we observed several waterfowls with avian influenza infection under telemetric monitoring. Based on the telemetry records and surveillance data, we conducted a case study to test hypotheses related to the transmission pathway between wild birds and poultry. One sedentary wildfowl naturally infected with HPAI H5N6, which overlapped with the home range of one migratory bird with H5-specific antibody-positive, showed itself to be phylogenetically close to the isolates from a chicken farm located within its habitat. Our study is the first observational study that provides scientific evidence supporting the hypothesis that the HPAI spillover into poultry farms is caused by local persistence in sedentary birds, in addition to its long-range dispersal by sympatric migratory birds. [ABSTRACT FROM AUTHOR]

The present study reports the clinical, virological and pathological findings observed in a natural outbreak of highly pathogenic avian influenza in farmed commercial ducks. The ducks developed clinical signs, including mild respiratory distress, depression, mild diarrhoea, loss of appetite and increasing mortality (up to 12%). Al necropsy, multifocal mottled necrosis was commonly found in the pancreas with splenomegaly, hepatomegaly, and swollen kidneys. Microscopically, there was necrotized pancreatitis and hepatitis, and lymphocytic meningoencephalitis and myocarditis. Influenza viral antigen was demonstrated in areas closely associated with histopathological lesion. Avian influenza virus was isolated from the caecal tonsil, faeces, and kidney of the domestic ducks. The isolated virus was identified as a highly pathogenic H5N1, with a haemagglutinin proteolytic cleavage site deduced amino acid sequence of... QRHKRKKR/GLFGAIAG ... In order to determine the pathogenicity of the isolate, eight 6-week-old specific pathogen free chickens were inoculated intravenously with the virus, and all birds died within 24 h after inoculation. This is the first report of an outbreak of highly pathogenic avian influenza with clinical signs in commercial domestic ducks in South Korea. [ABSTRACT FROM AUTHOR]

During the 2020–2021 winter season, an outbreak of clade 2.3.4.4b H5N8 high pathogenicity avian influenza (HPAI) virus occurred in South Korea. Here, we evaluated the pathogenicity and transmissibility of A/mandarin duck/Korea/H242/2020 (H5N8) (H242/20(H5N8)) first isolated from this outbreak in specific pathogen-free (SPF) chickens and commercial ducks in comparison with those of A/duck/Korea/HD1/2017(H5N6) (HD1/17(H5N6)) from a previous HPAI outbreak in 2017–2018. In chickens, the 50% chicken lethal dose and mean death time of H242/20(H5N8) group were 104.5 EID50 and 4.3 days, respectively, which indicate less virulent than those of HD1/17(H5N6) (103.6 EID50 and 2.2 days). Whereas, chickens inoculated with H242/20(H5N8) survived longer and had a higher titer of viral shedding than those inoculated with HD1/17(H5N6), which may increase the risk of viral contamination on farms. All ducks infected with either HPAI virus survived without clinical symptoms. In addition, they exhibited a longer virus shedding period and a higher transmission rate, indicating that ducks may play an important role as a silent carrier of both HPAI viruses. These results suggest that the pathogenic characteristics of HPAI viruses in chickens and ducks need to be considered to effectively control HPAI outbreaks in the field. [ABSTRACT FROM AUTHOR]

During October 2020–January 2021, we isolated a total of 67 highly pathogenic avian influenza (HPAI) H5N8 viruses from wild birds and outbreaks in poultry in South Korea. We sequenced the isolates and performed phylogenetic analysis of complete genome sequences to determine the origin, evolution, and spread patterns of these viruses. Phylogenetic analysis of the hemagglutinin (HA) gene showed that all the isolates belong to H5 clade 2.3.4.4 subgroup B (2.3.4.4b) and form two distinct genetic clusters, G1 and G2. The cluster G1 was closely related to the 2.3.4.4b H5N8 HPAI viruses detected in Europe in early 2020, while the cluster G2 had a close genetic relationship with the 2.3.4.4b H5N8 viruses that circulated in Europe in late 2020. A total of seven distinct genotypes were identified, including five novel reassortants carrying internal genes of low pathogenic avian influenza viruses. Our Bayesian discrete trait phylodynamic analysis between host types suggests that the viruses initially disseminated from migratory waterfowl to domestic duck farms in South Korea. Subsequently, domestic duck farms most likely contributed to the transmission of HPAI viruses to chicken and minor poultry farms, highlighting the need for enhanced, high levels of biosecurity measures at domestic duck farms to effectively prevent the introduction and spread of HPAI. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

H5Nx clade 2.3.4.4 highly pathogenic avian influenza viruses (HPAIVs) have been disseminated to wide geographic regions since 2014. In 2016, five distinct genotypes (C-1 to C-5) of clade 2.3.4.4c H5N6 HPAIVs were detected in South Korea. In this study, we evaluated the pathogenicity, susceptibility to infection, and transmissibility of the two strains representing the C-1 and C-4 genotypes of the H5N6 viruses, which have different PA and NS gene, in domestic ducks. Although the susceptibility to infection of domestic ducks to the two strains was similar, the C-4 genotype virus induced higher mortality in ducks than C-1 genotype virus. A higher titer of viral shedding were detected in ducks challenged with the C-4 genotype virus compared with the C-1 genotype virus. These results indicated that the reassortment of HPAIVs with prevailing low pathogenic avian influenza viruses could effect on the pathogenicity in ducks. • The two genotypes of H5N6 HPAI viruses showed different pathogenicity in ducks. • The C-4 genotype virus induced higher mortality in ducks than C-1 genotype virus. • The reassortment of HPAIVs could effect on the pathogenicity in ducks. [ABSTRACT FROM AUTHOR]

Abstract: We analyzed the evolution of H9 influenza viruses isolated from Korean chicken farms from 2002 to 2004. Korean H9 viruses formed two antigenically distinct groups: those isolated from 1996 to mid-2003, and those isolated from late 2003 through 2004. Most of the 2004 isolates showed greater cross-reactivity with the second group than with the first group. Phylogenetic analysis of the 12 viruses studied revealed three genotypes of H9N2 viruses and showed that reassortment had occurred. One isolate, Ck/Kor/164/04, belonged to the H9N8 subtype. Its HA and PB1 genes were similar to those of the H9N2 viruses, but its other genes were closely related to H3N8 viruses. This report is the first (to our knowledge) of H9N8 infection in this host. The pathogenicity of the early isolates altered due to antigenic drift and reassortment, leading to H9 avian influenza viruses in Korea that potentially can expand their host range to mammalians. [Copyright &y& Elsevier]