Human‐infecting influenza A (H9N2) virus: A forgotten potential pandemic strain?

Abstract

Continuously emergence of human infection with avian influenza A virus poses persistent threat to human health, as illustrated in H5N1, H7N9 and recent surge of H9N2 infections. Long-term prevalence of H9N2 avian influenza A virus in China and adjacent regions favours the interspecies transmissions from avian to human.Establishment of multiple genotypes of H9N2 variants in this region contributes to the emergence of novel H7N9 and H10N8 viruses which caused human fatalities.Recent increasing human infection with H9N2 virus in China highlights the necessity to closely monitor the interspecies transmission events. Available human H9N2 sequences revealed that Y280/G9 lineage was responsible for the most of human cases. Presence of adaptive mutations beyond the human-like receptor binding was indicative of the capacity of readily infecting new hosts without prior adaptation. Moreover, enlarged host range of H9N2 virus in this region substantially increased the transmission among mammals. Meanwhile, serological surveys implied human was more susceptible to H9N2 infection, compared with panzootic H5 and H7 subtype avian influenza virus. Thus, control at the source will be the ultimate and effective option for H9N2 pandemic preparedness. This review comprehensively summarized recent updates on H9N2 human infections, aiming to shed light on the prevention strategies against this strain with pandemic potential. K E Y W O R D SH9N2, influenza, pandemic

PA-X is an avian virulence factor in H9N2 avian influenza virus

“…H9N2 viruses cause massive economic damage due to their impact on poultry production systems, causing moderate morbidity and mortality, especially in the context of viral or bacterial coinfection. Additionally, H9N2 viruses pose a direct zoonotic threat to humans and are considered viruses with pandemic potential [18, 19]. As well as being zoonotic threats in their own right, H9N2 viruses have contributed polymerase genes to multiple zoonotic avian influenza viruses, including epidemic H7N9 [20].…”

Variation and Molecular Basis for Enhancement of Receptor Binding of H9N2 Avian Influenza Viruses in China Isolates

“…During 2005-2011, four human infection cases were reported. Notably, human infection cases of H9N2 viruses have been increasing to 28 during 2012-2019 (Song and Qin, 2020). Besides, it seems that H9N2 viruses currently circulating in poultry can easily transmit between species and infect different mammals.…”

The Causal Relationship between Eating Animals and Viral Epidemics

“…These viruses occur naturally among wild aquatic birds worldwide and can infect domestic poultry as well as wild birds and other animal species including humans. Avian flu viruses do not normally infect humans, but sporadic human infections caused by these viruses have been reported [Song and Qin, 2020]. AIV is also known as H5N1, and this virus has killed billions of poultry in Asia, North Africa, the Middle East, and the Americas.…”

“…These viruses aggressively infect domestic birds, wild ducks and geese, and other aquatic and migratory birds, spreading the disease around the world, evolving through ongoing mutation and natural selection. These viruses continue to evolve and adapt to multiple reservoir hosts, including humans, and they pose major threats globally to the poultry industry as well as to people [Song and Qin, 2020]. Like swine influenza virus, discussed in the next section, the continuous recombination of viral RNA, going on in our huge domestic flocks and herds, explains why we need to keep making new vaccines each year, and why international cooperation in monitoring the emergence of new strains is so important.…”