Genetic and biological characteristics of the globally circulating H5N8 avian influenza viruses and the protective efficacy offered by the poultry vaccine currently used in China

The H5N8 avian influenza viruses have been widely circulating in wild birds and are responsible for the loss of over 33 million domestic poultry in Europe, Russia, Middle East, and Asia since January 2020. To monitor the invasion and spread of the H5N8 virus in China, we performed active surveillance by analyzing 317 wild bird samples and swab samples collected from 41,172 poultry all over the country. We isolated 22 H5N8 viruses from wild birds and 14 H5N8 viruses from waterfowls. Genetic analysis indicated that the 36 viruses formed two different genotypes: one genotype viruses were widely detected from different wild birds and domestic waterfowls; the other genotype was isolated from a whopper swan. We further revealed the origin and spatiotemporal spread of these two distinct H5N8 virus genotypes in 2020 and 2021. Animal studies indicated that the H5N8 isolates are highly pathogenic to chickens, mildly pathogenic in ducks, but have distinct pathotypes in mice. Moreover, we found that vaccinated poultry in China could be completely protected against H5N8 virus challenge. Given that the H5N8 viruses are likely to continue to spread in wild birds, vaccination of poultry is highly recommended in high-risk countries to prevent H5N8 avian influenza.

Disentangling the role of poultry farms and wild birds in the spread of highly pathogenic avian influenza virus H5N8 in Europe

Recent outbreaks of highly pathogenic avian influenza H5N8 virus in Europe have caused severe damage to animal health, wildlife conservation and livestock economic sustainability. While epidemiological and phylogenetic studies have generated important clues about the virus spread in Europe, they remained opaque to the specific role of poultry farms and wild birds. Using a phylodynamic framework, we inferred the H5N8 virus transmission dynamics among poultry farms and wild birds in four severely affected countries and investigated drivers of spread between farms across borders during the 2016-17 epidemic. Based on existing genetic data, we showed that the virus was likely introduced into poultry farms during the autumn, in line with the timing of arrival of migratory wild birds. Then, transmission was mainly driven by farm-to-farm transmission in Germany, Hungary and Poland, suggesting that better understanding of how infected farms are connected in those countries would greatly help control efforts. In contrast, the epidemic was dominated by wild bird-to-farm transmission in Czech Republic, meaning that more sustainable prevention strategies should be developed to reduce virus exposure from wild birds. We inferred effective reproduction number Re estimates among poultry farms and wild birds. We expect those estimates being useful to parameterize predictive models of virus spread aiming at optimising control strategies. None of the investigated predictors related to live poultry trade, poultry census and geographic proximity were identified as supportive predictors of the viral spread between farms across borders, suggesting that other drivers should be considered in future studies.

Epidemiology, Genetic Characterization, and Pathogenesis of Avian Influenza H5N8 Viruses Circulating in Northern and Southern Parts of Egypt, 2017–2019

Highly pathogenic avian influenza (HPAI) viruses of subtype H5N8 continue to circulate, causing huge economic losses and serious impact on poultry production worldwide. Recently, HPAIV H5N8 has been spreading rapidly, and a large number of HPAI H5N8 outbreaks have been reported in Eurasia 2020–2021. In this study, we conducted an epidemiological survey of HPAI H5N8 virus at different geographical locations in Egypt from 2017 to 2019. This was followed by genetic and pathogenic studies. Our findings highlight the wide spread of HPAI H5N8 viruses in Egypt, including in 22 governorates. The genetic analyses of the hemagglutinin (HA) and neuraminidase (NA) gene segments emphasized a phylogenetic relatedness between the Egyptian HPAI H5N8 viruses and viruses of clade 2.3.4.4b recently isolated in Europe. These findings suggest that a potential back transmission of Egyptian HPAI H5N8 virus has occurred from domestic poultry in Egypt to migratory wild birds, followed by further spread to different countries. This highlights the importance of continuous epidemiological and genetic studies of AIVs at the domestic–wild bird interface.

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, HA clades 2.3.4.4A and 2.3.4.4B, caused intercontinental outbreaks in 2014-2015 and 2016-2017 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 PB2, NP, and M reassortants. No differences in morbidity and mortality were observed with reassortants that either have the polymerase complex segments or the HA and NA segments of the 2016 virus in the genetic backbone of the 2014 virus. In vitro assays showed that the NP and 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 highly pathogenic avian influenza (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 have 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 has potential implications in the ecology and epidemiology of H5Nx HPAI in wild bird populations.

Isolation of clade 2.3.4.4b A(H5N8), a highly pathogenic avian influenza virus, from a worker during an outbreak on a poultry farm, Russia, December 2020

This study presents the isolation of influenza A(H5N8) virus clade 2.3.4.4b from a poultry worker during an outbreak of highly pathogenic avian influenza A(H5N8) among chickens at a poultry farm in Astrakhan, Russia in December 2020. Nasopharyngeal swabs collected from seven poultry workers were positive for influenza A(H5N8), as confirmed by RT-PCR and sequencing. The influenza A(H5N8) virus was isolated from one of the human specimens and characterised. Sporadic human influenza A(H5)2.3.4.4. infections represent a possible concern for public health.