A novel reassortant clade 2.3.4.4 highly pathogenic avian influenza H5N6 virus identified in South Korea in 2018

Concurrent Infection with Clade 2.3.4.4b Highly Pathogenic Avian Influenza H5N6 and H5N1 Viruses, South Korea, 2023

Highly pathogenic avian influenza H5N6 and H5N1 viruses of clade 2.3.4.4b were simultaneously introduced into South Korea at the end of 2023. An outbreak at a broiler duck farm consisted of concurrent infection by both viruses. Sharing genetic information and international surveillance of such viruses in wild birds and poultry is critical.

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.

Pathogenicity in Chickens and Turkeys of a 2021 United States H5N1 Highly Pathogenic Avian Influenza Clade 2.3.4.4b Wild Bird Virus Compared to Two Previous H5N8 Clade 2.3.4.4 Viruses

Highly pathogenic avian influenza viruses (HPAIVs) of subtype H5 of the Gs/GD/96 lineage remain a major threat to poultry due to endemicity in wild birds. H5N1 HPAIVs from this lineage were detected in 2021 in the United States (U.S.) and since then have infected many wild and domestic birds. We evaluated the pathobiology of an early U.S. H5N1 HPAIV (clade 2.3.4.4b, 2021) and two H5N8 HPAIVs from previous outbreaks in the U.S. (clade 2.3.4.4c, 2014) and Europe (clade 2.3.4.4b, 2016) in chickens and turkeys. Differences in clinical signs, mean death times (MDTs), and virus transmissibility were found between chickens and turkeys. The mean bird infective dose (BID50) of the 2021 H5N1 virus was approximately 2.6 log10 50% embryo infective dose (EID50) in chickens and 2.2 log10 EID50 in turkeys, and the virus transmitted to contact-exposed turkeys but not chickens. The BID50 for the 2016 H5N8 virus was also slightly different in chickens and turkeys (4.2 and 4.7 log10 EID50, respectively); however, the BID50 for the 2014 H5N8 virus was higher for chickens than turkeys (3.9 and ~0.9 log10 EID50, respectively). With all viruses, turkeys took longer to die (MDTs of 2.6-8.2 days for turkeys and 1-4 days for chickens), which increased the virus shedding period and facilitated transmission to contacts.

Estimation of Avian Influenza Viruses in Water Environments of Live Poultry Markets in Changsha, China, 2014 to 2018

In routine surveillance for avian influenza viruses (AIVs) in the environments of live poultry markets (LPMs), certain samples were positive for AIVs type A while negative for subtypes (e.g., H5, H7, and H9). However, little attention has been paid to these unsubtyped AIVs samples. To reveal the dynamic distribution and molecular characteristics of AIVs, especially the unsubtyped AIVs, we reported and analyzed 1969 samples collected from the water environments of LPMs in Changsha, China, from January 2014 to November 2018. Our results revealed that 1504 (76.38%) samples were positive for AIV type A. Of these samples, the predominant hemagglutinin (HA) subtype was H9, followed by H5 and H7 (P < 0.05). The positive rate of H5 subtype in water environmental samples exhibited seasonality, which reached a peak in each winter-spring season from January 2014 to March 2017. The positive rates of AIVs (including type A, subtype H9, and mixed subtype H5/H7/H9) in non-central-city regions were higher than that in the central-city regions (P < 0.05). Notably, 161 unsubtyped AIVs samples were detected during the routine surveillance. However, subtyping with the commercial kit further identified eight different HA and seven different neuraminidase subtypes. Analyses unraveled that further subtyped AIVs H1, H6, and H11 had only one basic amino acid (R or K) at the cleavage site and residues Q²²⁶ and G²²⁸ at the receptor-binding associated sites. Overall, in addition to H5, H7, and H9 subtypes, we should also pay attention to unsubtyped AIVs samples during the routine surveillance for AIVs in the environments of LPMs.

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

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 10^4.5 EID₅₀ and 4.3 days, respectively, which indicate less virulent than those of HD1/17(H5N6) (10^3.6 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.

Multiple Gene Segments Are Associated with Enhanced Virulence of Clade 2.3.4.4 H5N8 Highly Pathogenic Avian Influenza Virus in Mallards

Highly pathogenic avian influenza (HPAI) viruses from the H5Nx Goose/Guangdong/96 lineage continue to cause outbreaks in domestic and wild bird populations. Two distinct genetic groups of H5N8 HPAI viruses, hemagglutinin (HA) clades 2.3.4.4A and 2.3.4.4B, caused intercontinental outbreaks in 2014 to 2015 and 2016 to 2017, respectively. Experimental infections using viruses from these outbreaks demonstrated a marked difference in virulence in mallards, with the H5N8 virus from 2014 causing mild clinical disease and the 2016 H5N8 virus causing high mortality. To assess which gene segments are associated with enhanced virulence of H5N8 HPAI viruses in mallards, we generated reassortant viruses with 2014 and 2016 viruses. For single-segment reassortants in the genetic backbone of the 2016 virus, pathogenesis experiments in mallards revealed that morbidity and mortality were reduced for all eight single-segment reassortants compared to the parental 2016 virus, with significant reductions in mortality observed with the polymerase basic protein 2 (PB2), nucleoprotein (NP), and matrix (M) reassortants. No differences in morbidity and mortality were observed with reassortants that either have the polymerase complex segments or the HA and neuraminidase (NA) segments of the 2016 virus in the genetic backbone of the 2014 virus. In vitro assays showed that the NP and polymerase acidic (PA) segments of the 2014 virus lowered polymerase activity when combined with the polymerase complex segments of the 2016 virus. Furthermore, the M segment of the 2016 H5N8 virus was linked to filamentous virion morphology. Phylogenetic analyses demonstrated that gene segments related to the more virulent 2016 H5N8 virus have persisted in the contemporary H5Nx HPAI gene pool until 2020. IMPORTANCE Outbreaks of H5Nx HPAI viruses from the goose/Guangdong/96 lineage continue to occur in many countries and have resulted in substantial impact on wild birds and poultry. Epidemiological evidence has shown that wild waterfowl play a major role in the spread of these viruses. While HPAI virus infection in gallinaceous species causes high mortality, a wide range of disease outcomes has been observed in waterfowl species. In this study, we examined which gene segments contribute to severe disease in mallards infected with H5N8 HPAI viruses. No virus gene was solely responsible for attenuating the high virulence of a 2016 H5N8 virus, but the PB2, NP, and M segments significantly reduced mortality. The findings herein advance our knowledge on the pathobiology of avian influenza viruses in waterfowl and have potential implications on the ecology and epidemiology of H5Nx HPAI in wild bird populations.

Highly Pathogenic Avian Influenza Clade 2.3.4.4b Subtype H5N8 Virus Isolated from Mandarin Duck in South Korea, 2020

In October 2020, a highly pathogenic avian influenza (HPAI) subtype H5N8 virus was identified from a fecal sample of a wild mandarin duck (Aix galericulata) in South Korea. We sequenced all eight genome segments of the virus, designated as A/Mandarin duck/Korea/K20-551-4/2020(H5N8), and conducted genetic characterization and comparative phylogenetic analysis to track its origin. Genome sequencing and phylogenetic analysis show that the hemagglutinin gene belongs to H5 clade 2.3.4.4 subgroup B. All genes share high levels of nucleotide identity with H5N8 HPAI viruses identified from Europe during early 2020. Enhanced active surveillance in wild and domestic birds is needed to monitor the introduction and spread of HPAI via wild birds and to inform the design of improved prevention and control strategies.

Avian influenza overview August - November2019

Between 16 August and 15 November 2019, one low pathogenic avian influenza (LPAI) A(H5) outbreak in poultry in France was reported in Europe. Genetic characterisation reveals that the virusclusterswith Eurasian LPAI viruses. No highly pathogenic avian influenza (HPAI) outbreaks in birds were notified in Europe in the relevant period for this report. HPAI A(H5N6) viruswas identified in chickens in Nigeria, this isthe first report of HPAI A(H5N6) from the African continent.FewerHPAI outbreaks in Asia and Africa were reported during the time period for this report compared with the previous reporting period. Apart from the long‐term epidemic of HPAI A(H5N2)in Taiwan, only six HPAI outbreakswere reported in domestic birds from Nepal, South Africa and Taiwan. Furthermore, no HPAI detections fromwild birds were reported worldwide in the relevant time period forthis report.Even if the risk of incursion of HPAI from wild birds into poultryestablishments in Europe is currently assessed as low, it is important to maintain passive surveillance activities. The focus should be on wild bird species that are in the revised list of target species in order to detect any incursion of HPAI virus early and initiate a warning.Despite the decrease in the number of avian influenza outbreaks over recent months, it is important to maintain a high alert level andhigh standard of biosecurity onpoultry establishments.In Europe, no human infections due toHPAI viruses detected in wild bird or poultry outbreaks, have been reported. The risk of zoonotic transmission to the general public in Europe is considered to be very low.

Sub-Saharan Africa and Eurasia Ancestry of Reassortant Highly Pathogenic Avian Influenza A(H5N8) Virus, Europe, December 2019

We report detection of a highly pathogenic avian influenza A(H5N8) clade 2.3.4.4b virus in Europe. This virus was generated by reassortment between H5N8 subtype virus from sub-Saharan Africa and low pathogenicity avian influenza viruses from Eurasia.

Highly pathogenic H5N6 avian influenza virus subtype clade 2.3.4.4 indigenous in South Korea

The outbreaks of the highly pathogenic avian influenza (HPAI) in 2016–2017 and 2017–2018, caused by novel reassortant clade 2.3.4.4 H5N6 viruses, resulted in the loss of one billion birds in South Korea. Here, we characterized the H5N6 viruses isolated from wild birds in South Korea from December 2017 to August 2019 by next-generation sequencing. The results indicated that clade 2.3.4.4 H5N6 viruses isolated in 2017 and 2019 shared almost identical nucleotide sequences with the HPAI H5N6 viruses from 2016 in South Korea. This repeated detection of evolutionarily identical H5N6 viruses in same region for more than three years may suggest indigenization of the HPAI H5N6 virus in South Korea. Phylogenetic analysis demonstrated that the clade 2.3.4.4 H5N6 viruses isolated in 2017 and 2019 were evolutionarily distinct from those isolated in 2018. Molecular analysis revealed that the H5N6 viruses isolated in 2017 and 2019 had features associated with an increased risk of human infection (e.g. a deletion at position 133 of HA and glutamic acid residue at position 92 of NS1). Overall, these genomic features of HPAI H5N6 viruses highlight the need for continuous monitoring of avian influenza viruses in wild migratory birds as well as in domestic birds.