A 627K variant in the PB2 protein of H9 subtype influenza virus in wild birds

Wild Bird-Origin H6N2 Influenza Virus Acquires Enhanced Pathogenicity after Single Passage in Mice

The H6 subtype of avian influenza viruses (AIVs) has emerged as one of the predominant subtypes in both wild and domestic avian species. Currently, H6 AIVs have acquired the ability to infect a wide range of mammals, though the related molecular mechanisms have yet to be fully investigated. In this study, a wild bird-origin H6N2 AIV was isolated from the East Asian-Australasian migratory flyway region located in Liaoning Province. This H6N2 virus initially expressed limited replication in mice. However, after one passage in mice, the virus acquired two mutations, PB2 E627K and HA A110V. The mutant displayed enhanced replication both in vitro and in vivo, proving lethal to mice. But the mutant retained the α-2, 3-linked sialic acid binding property and failed to transmit in guinea pigs. We explored the molecular mechanisms underlying the pathogenicity difference between the wild type and the mutant. Our findings revealed that PB2 E627K dramatically enhanced the polymerase activity of the H6N2 virus, while the HA A110V mutation decreased the pH of HA activation. This study demonstrated that the H6N2 subtype wild bird-origin AIV easily acquired the mammalian adaptation. The monitoring and evaluation of H6 wild bird-origin AIV should be strengthened.

Enhanced pathogenicity and transmissibility of H9N2 avian influenza virus in mammals by hemagglutinin mutations combined with PB2-627K

H9N2 avian influenza viruses (AIVs) circulate globally in poultry and have become the dominant AIV subtype in China in recent years. Previously, we demonstrated that the H9N2 virus (A/chicken/Eastern China/SDKD1/2015) naturally harbors a mammalian-adaptive molecular factor (627K) in the PB2 protein and is weakly pathogenic in mice. Here, we focused on new markers for virulence in mammals. A mouse-adapted H9N2 virus was serially passaged in mice by infecting their lungs. As expected, infected mice showed clinical symptoms and died at passage six. A comparison between the wild-type and mouse-adapted virus sequences identified amino acid substitutions in the hemagglutinin (HA) protein. H9N2 viruses with the T187P ​+ ​M227L double mutation exhibited an increased affinity to human-type (SAα2,6Gal) receptors and significantly enhanced viral attachment to mouse lung tissues, which contributed to enhancing viral replication and virulence in mice. Additionally, HA with the T187P ​+ ​M227L mutation enabled H9N2 viral transmission in guinea pigs via direct contact. AIV pathogenicity in mice is a polygenic trait. Our results demonstrated that these HA mutations might be combined with PB2-627K to significantly increase H9N2 virulence in mice, and this enhanced virulence was achieved in other H9N2 AIVs by generating the same combination of mutations. In summary, our study identified novel key elements in the HA protein that are required for H9N2 pathogenicity in mice and provided valuable insights into pandemic preparedness against emerging H9N2 strains.

Emergence and Evolution of Novel Canine-Avian Reassortant H3N2 Influenza A Viruses in Duck in Leizhou Peninsula, China

Avian-to-mammal transmission and mammalian adaptation of avian influenza virus (AIV) are threats to public health and of great concern. The H3 subtype of influenza virus has low pathogenicity and is widely distributed in humans, canines, equines and avians. In 2018–2019, we isolated six H3N2 subtype influenza viruses from 329 samples acquired from ducks on the Leizhou Peninsula, China, as part of an ongoing virus surveillance program. All viruses were analyzed by whole-genome sequencing with subsequent genetic comparison and phylogenetic analysis. Phylogenetic analysis demonstrated that reassortment of these viruses has occurred among different hosts and subtypes. Some of the H3 AIV isolates have similar genes as subtypes H5 and H7 of highly pathogenic avian influenza viruses (HPAIVs). Most importantly, one strain of H3N2 virus is a novel reassortant influenza virus containing HA and PB2 segments from canine H3N2 virus. The time of most recent common ancestor (tMRCA) data indicated that this reassortant H3N2 virus might have emerged in 2011–2018. The findings suggest that the viruses studied here have undergone multiple reassortment events. Our results provide a framework for understanding the molecular basis of host-range shifts of influenza viruses and we should pay more attention to canine which lived with avian together.

Genetic and Molecular Characterization of H9N2 Avian Influenza Viruses Isolated from Live Poultry Markets in Hubei Province, Central China, 2013-2017

H9N2 subtype avian influenza virus (AIV) is an influenza A virus that is widely spread throughout Asia, where it jeopardizes the poultry industry and provides genetic material for emerging human pathogens. To better understand the epidemicity and genetics of H9 subtype AIVs, we conducted active surveillance in live poultry markets (LPMs) in Hubei Province from 2013 to 2017. A total of 4798 samples were collected from apparent healthy poultry and environment. Real-time RT-PCR revealed that the positivity rate of influenza A was 26.6% (1275/4798), of which the H9 subtype accounted for 50.3% (641/1275) of the positive samples. Of the 132 H9N2 viral strains isolated, 48 representative strains were subjected to evolutionary analysis and genotyping. Phylogenetic analysis revealed that all H9N2 viral genes had 91.1%-100% nucleotide homology, clustered with genotype 57, and had high homology with human H9N2 viruses isolated from 2013 to 2017 in China. Using a nucleotide divergence cutoff of 95%, we identified ten distinct H9N2 genotypes that continued to change over time. Molecular analysis demonstrated that six H9N2 isolates had additional potential glycosylation sites at position 218 in the hemagglutinin protein, and all isolates had I155T and Q226L mutations. Moreover, 44 strains had A558V mutations in the PB2 protein and four had E627V mutations, along with H9N2 human infection strains A/Beijing/1/2016 and A/Beijing/1/2017. These results emphasize that the H9N2 influenza virus in Hubei continues to mutate and undergo mammalian adaptation changes, indicating the necessity of strengthening the surveillance of the AIV H9N2 subtype in LPMs.

Avian influenza overview May - August 2018

Between 16 May and 15 August 2018, three highly pathogenic avian influenza (HPAI) A(H5N8) outbreaks in poultry establishments and three HPAI A(H5N6) outbreaks in wild birds were reported in Europe. Three low pathogenic avian influenza (LPAI) outbreaks were reported in three Member States. Few HPAI and LPAI bird cases have been detected in this period of the year, in accordance with the seasonal expected pattern of LPAI and HPAI. There is no evidence to date that HPAI A(H5N8) and A(H5N6) viruses circulating in Europe have caused any human infections. The risk of zoonotic transmission to the general public in Europe is considered to be very low. Several HPAI outbreaks in poultry were reported during this period from Russia. The presence of the A(H5N2) and A(H5N8) viruses in parts of Russia connected with fall migration routes of wild birds is of concern for possible introduction and spread with wild birds migrating to the EU. Although few AI outbreaks were observed in Africa, Asia and the Middle East during the reporting period, the probability of AI virus introductions from non‐EU countries via wild birds particularly via the north‐eastern route from Russia is increasing, as the fall migration of wild birds will start in the coming weeks. Further, the lower temperatures in autumn and winter may facilitate the environmental survival of avian influenza viruses potentially introduced to Europe.

A 627K variant in the PB2 protein of H9 subtype influenza virus in wild birds

BACKGROUND

Wild birds are gaining increasing attention as gene-mixing reservoirs for influenza viruses. To investigate the molecular properties of the viruses isolated and epidemiological analysis of H9N2 subtype AIV in wild birds, we studied samples obtained over two years (2014-2015) from wetlands in Anhui province, China.

METHODS

A total of 4534 samples were collected from migratory waterfowl in Anhui in 2014-2015, and 8 strains of H9 subtype AIV were isolated.

RESULTS

Phylogenetic analysis showed different degrees of gene segment reassortment in H9 viruses between the Eurasian lineage and the North American lineage. Most importantly, two viruses harbored the E627K mutation in the polymerase PB2 (PB2) protein. This is the first report of the mutation of this virus from low pathogenicity to high pathogenicity in wild birds.

CONCLUSIONS

The continued surveillance of wild birds, especially migratory birds, is important to provide early warning and control of AIV outbreaks. Our results highlight the high genetic diversity of AIV along the Eurasian-Australian migration flyway and the need for more extensive AIV surveillance in eastern China.