The recent human infection with avian influenza virus revealed that H9N2 influenza virus is the gene donor for H7N9 and H10N8 viruses infecting humans. The crucial role of H9N2 viruses at the animal-human interface might be due to the wide host range, adaptation in both poultry and mammalian, and extensive gene reassortment. As the most prevalent subtype of influenza viruses in chickens in China, H9N2 also causes a great economic loss for the poultry industry, even under the long-term vaccination programs. The history, epidemiology, biological characteristics, and molecular determinants of H9N2 influenza virus are reviewed in this paper. The contribution of H9N2 genes, especially RNP genes, to the infection of humans needs to be investigated in the future.
Animals ; Chickens ; virology ; China ; epidemiology ; Humans ; Influenza A Virus, H7N9 Subtype ; genetics ; Influenza A Virus, H9N2 Subtype ; genetics ; immunology ; physiology ; Influenza in Birds ; epidemiology ; transmission ; virology ; Influenza, Human ; epidemiology ; transmission ; virology ; Vaccination ; Viral Proteins ; classification ; metabolism

Animals ; Asian Continental Ancestry Group ; Chickens ; China ; epidemiology ; Cytokines ; metabolism ; Genetic Variation ; Genotype ; Humans ; Influenza A Virus, H7N9 Subtype ; classification ; genetics ; pathogenicity ; Influenza A Virus, H9N2 Subtype ; genetics ; Influenza in Birds ; transmission ; virology ; Influenza, Human ; ethnology ; transmission ; virology ; Mice, Inbred BALB C ; Molecular Sequence Data ; Orthomyxoviridae Infections ; metabolism ; mortality ; virology ; Phylogeny ; Seasons ; Survival Rate ; Virulence ; genetics

The primary determinant of influenza virus infectivity is the type of linkage between sialic acid and oligosaccharides on the host cells. Hemagglutinin of avian influenza viruses preferentially binds to sialic acids linked to galactose by an alpha-2,3 linkage whereas hemagglutinin of human influenza viruses binds to sialic acids with an alpha-2,6 linkage. The distribution patterns of influenza receptors in the avian respiratory tracts are of particular interest because these are important for initial viral attachment, replication, and transmission to other species. In this study, we examined the distribution patterns of influenza receptors in the respiratory tract of chickens, ducks, pheasants, and quails because these species have been known to act as intermediate hosts in interspecies transmission. Lectin histochemistry was performed to detect receptor-bearing cells. Cell-specific distribution of the receptors was determined and expression densities were compared. We observed species-, site-, and cell-specific variations in receptor expression. In general, receptor expression was the highest in quails and lowest in ducks. Pheasants and quails had abundant expression of both types of receptors throughout the respiratory tract. These results indicate that pheasants and quails may play important roles as intermediate hosts for the generation of influenza viruses with pandemic potential.
Animals ; Cell Membrane/metabolism/virology ; Hemagglutinin Glycoproteins, Influenza Virus/metabolism ; Host-Pathogen Interactions ; Influenza A virus/*metabolism ; Influenza in Birds/metabolism/transmission ; Lectins/metabolism ; Poultry/metabolism/*virology ; Poultry Diseases/metabolism ; Receptors, Cell Surface/analysis/chemistry/metabolism ; Receptors, Virus/*analysis/metabolism ; Respiratory System/*chemistry ; Sialic Acids/metabolism ; Species Specificity ; Specific Pathogen-Free Organisms