Search

Pigeon paramyxovirus type 1 (PPMV‐1) is an antigenic variant of Newcastle disease virus (NDV) which is mainly associated with infections of pigeons and has the potential to result in disease in chickens. In this study, we characterised 21 PPMV‐1 isolates from diseased pigeons in China during 2007–2019. Phylogenetic analysis revealed that all isolates belonged to genotype VI. Among them, most isolates belonged to sub‐genotype VI.2.1.1.2.2, suggesting that VI.2.1.1.2.2 has become a prevalent genotype in pigeons in China. The results showed that all PPMV‐1 isolates were mesogenic in nature according to the mean death time (MDT) and intracerebral pathogenicity index (ICPI). In vitro and in vivo studies demonstrated that two genetically closely related isolates (Pi‐11 and Pi‐10) both of which belonged to sub‐genotype VI.2.1.1.2.2 had similar replication kinetics in cells derived from pigeons, while the replication titre of Pi‐11 was significantly higher than that of Pi‐10 in cells derived from chickens. Pi‐11 and Pi‐10 could contribute to morbidity and mortality in pigeons. Remarkably, although the two viruses resulted in no apparent disease symptom in chickens, Pi‐11 could cause more severe histopathological lesions and had a stronger replication ability in chickens compared to Pi‐10. Moreover, chickens infected with Pi‐11 had higher shedding efficiency than chickens infected with Pi‐10. Additionally, several mutations within important functional regions of the fusion (F) and haemagglutinin‐neuraminidase (HN) proteins might be associated with different pathogenicity of the two viruses in chickens. Collectively, these results indicated that the Pi‐11‐like virus of pigeon origin has the potential to induce severe outbreaks in chicken flocks. These findings will help us better understand the epidemiology and evolution of PPMV‐1 in China and serve as a foundation for the further investigation of the mechanism underlying the pathogenic difference of PPMV‐1 isolates in chickens. [ABSTRACT FROM AUTHOR]

In recent years in China, clade 2.3.4.4 H5N6 plus clade 2.3.2.1 H5N1 subtype highly pathogenic avian influenza (HPAI) viruses have gradually become endemic in poultry, and their co‐circulation could inevitably facilitate the gene reassortment between each other. During our routine surveillance in live poultry markets (LPMs) in eastern China in 2017–2018, a novel reassortant H5N6 strain with the HA gene derived from clade 2.3.2.1 was isolated from the cloacal swabs of apparently healthy ducks. Phylogenetic tracing analysis indicated that another two clade 2.3.2.1 H5N1 strains with divergent lineages of PB1 gene and one clade 2.3.4.4 H5N6 isolate of the dominant genotype sharing spatio‐temporal proximity were intimately involved in the generation of this rarely reported clade 2.3.2.1 H5N6 reassortant. Distinct with the other three HPAI H5 viruses showing moderate virulence in mice, the H5N1 strain of the homologous internal gene constellation against the clade 2.3.2.1 H5N6 reassortant was highly pathogenic, which might probably attribute to the H3 subtype‐derived PB1 gene. However, as compared to the clade 2.3.4.4 H5N6 ancestor, the clade 2.3.2.1 H5N6 reassortant displayed a broader tissue distribution and higher viral titres in mice, which could likely facilitate the viral maintenance and spread in nature. Therefore, our results highlight that continuous epidemiological survey of H5 subtype HPAI viruses in LPMs needs to be strengthened to prevent the potential poultry or even public health threat of the novel reassortants from endemic viruses. [ABSTRACT FROM AUTHOR]

Pre‐existing immunity against the conserved haemagglutinin (HA) stalk underlies the elicitation of cross‐group antibody induced by natural H7N9 virus infection and immunization in humans. However, whether broadly reactive antibodies can be induced by H7N9 infection and immunization in the absence of pre‐existing stalk‐specific immunity is unclear. In this study, antibody response induced by H7N9 virus infection and immunization with inactivated and viral‐vectored H7N9 vaccines in naïve chickens was analysed. The results showed that H7N9 infection and immunization with inactivated vaccine resulted in potent induction of haemagglutination‐inhibition (HI), virus neutralization (VN) and HA‐binding antibodies, whereas Newcastle disease virus (NDV)‐vectored H7N9 vaccine induced marginal HI and VN titres but high levels of HA‐binding antibody. In addition, H7N9 infection and immunization induced stalk‐specific antibodies in naïve chickens and these antibodies recognized different epitopes in the stalk. Virus infection and immunization with inactivated vaccine elicited antibodies cross‐reactive with both group 1 and group 2 HAs, while antibodies induced by NDV‐H7N9 vaccination showed a narrower cross‐reactivity within group 2. Moreover, only homologous neutralizing activity of the sera against H7N9 virus was observed, and cross‐binding antibodies did not show heterosubtypic neutralizing activity. Our results indicated that cross‐group binding but non‐neutralizing antibodies primarily targeting the stalk can be induced by natural H7N9 infection and immunization with inactivated vaccine in naïve chickens. This suggests that at least in a naïve chicken model, pre‐existing stalk‐specific immunity is not required for induction of broadly reactive antibodies. Additionally, H7N9‐based immunogens may be explored as vaccine candidates or as a prime component to induce broadly protective influenza immunity. [ABSTRACT FROM AUTHOR]

Genotype S H9N2 avian influenza virus, which has been predominant in China since 2010, contributed its entire internal gene cassette to the genesis of novel reassortant influenza viruses, including H5Nx, H7N9 and H10N8 viruses that pose great threat to poultry and humans. A key feature of the genotype S H9N2 virus is the substitution of G1‐like M and PB2 genes for the earlier F/98‐like M and PB2 of genotype H virus. However, how this gene substitution has influenced viral adaptability of emerging influenza viruses in mammals remains unclear. We report here that reassortant H5Nx and H7N9 viruses with the genotype S internal gene cassette displayed enhanced replication and virulence over those with genotype H internal gene cassette in cell cultures as well as in the mouse models. We showed that the G1‐like PB2 gene was associated with increased polymerase activity and improved nuclear accumulation compared with the F/98‐like counterpart, while the G1‐like M gene facilitated effective translocation of RNP to cytoplasm. Our findings suggest that the genotype S H9N2 internal gene cassette, which possesses G1‐like M and PB2 genes, is superior to that of genotype H, in optimizing viral fitness, and thus have implications for assessing the potential risk of these gene introductions to generate emerging influenza viruses. [ABSTRACT FROM AUTHOR]

As one of the important control strategies for highly pathogenic avian influenza (HPAI) in China, vaccination has been implemented compulsively in poultry flocks since 2004. However, the emergence and dominance of the circulating antigenic variants require the update of vaccines periodically. In order to investigate the key molecular sites responsible for the antigenic drift, a total of 13 amino acid positions divergent between clade 2.3.4 H5 viruses and their descendent subclade 2.3.4.4 variants in or around the recognized antigenic epitopes A–E were initially identified through inspecting a comprehensive HA sequence alignment of the H5 subtype HPAI viruses. Subsequently, a panel of single‐site or multi‐site HA mutants was constructed by reverse genetics with two H5N1 viruses of S (clade 2.3.4) and QD1 (subclade 2.3.4.4) as the HA backbone to study their antigenic variations, respectively. The hemagglutination–inhibition assay revealed an evident impact of mutations at sites 88, 156, 205, 208, 239 and 289 to the HA antigenicity and highlighted that the amino acid substitutions located in the antigenic region B, especially the combined mutations at sites 205 and 208, were the major antigenic determinant which was also consistent with results from flow cytometry and antigenic mapping. Our findings provided more insights into the molecular mechanism of antigenic drift of the H5 subtype HPAI virus, which would be helpful for the selection of vaccine candidates and accordingly for the prevention and control of this devastating viral agent. [ABSTRACT FROM AUTHOR]

Before 2013, zoonotic influenza infections were dominated by H5N1 viruses in China. However, the emergence of the H7N9 viruses in early 2013 changed this dominance greatly, and more than 1,600 laboratory‐confirmed human cases of H7N9 infections have been reported since then. To understand the underlying mechanism of the emergence of the fifth epidemic wave that shows an unexpected sharp increase, we systematically investigated the biological characteristics of the highly pathogenic (HP) and low‐pathogenic (LP) H7N9 AIVs during this period. We first systematically analysed the haemagglutination assay gene of all the isolates available from the website and found that the HP and LP viruses differed a little in the well‐established receptor binding sites and in other potentially important sites. Phylogenetic analysis showed that both the HP and LP viruses belong to the branch of the Yangtze River Delta, whereas they diverged to different small branches. To further compare the biological variations in the HP and LP viruses, we selected six HP and six LP strains for in‐depth analysis, including receptor binding characteristics, thermal stability, viral replication and virulence in mice. The three major findings of this study were as follows: (a) Other potential site/sites may affect the receptor binding property of the H7N9 viruses; (b) the HP viruses displayed a higher thermostability than did the LP viruses, quite consistent with the epidemiological data during the summer period; and (c) one‐third of the HP viruses were moderately pathogenic in mice, whereas all the LP viruses were nonpathogenic in this animal model. However, the LP viruses replicated more efficiently in the mouse lung and can spread to the extrarespiratory organs (spleen, kidney and brain). Taken together, our results suggest that both the HP and LP H7N9 viruses can pose a potential threat to public health, highlighting the importance of the continual surveillance of the H7N9 AIVs. [ABSTRACT FROM AUTHOR]