title: Human H7N9 avian influenza virus infection: a review and pandemic risk assessment.
abstract: China is undergoing a recent outbreak of a novel H7N9 avian influenza virus (nH7N9) infection that has thus far involved 132 human patients, including 37 deaths. The nH7N9 virus is a reassortant virus originating from the H7N3, H7N9 and H9N2 avian influenza viruses. nH7N9 isolated from humans contains features related to adaptation to humans, including a Q226L mutation in the hemagglutinin cleavage site and E627K and D701N mutations in the PB2 protein. Live poultry markets provide an environment for the emergence, spread and maintenance of nH7N9 as well as for the selection of mutants that facilitate nH7N9 binding to and replication in the human upper respiratory tract. Innate immune suppression conferred by the internal genes of H9N2 may contribute to the virulence of nH7N9. The quail may serve as the intermediate host during the adaptation of avian influenza viruses from domestic waterfowl to gallinaceous poultry, such as chickens and related terrestrial-based species, due to the selection of viral mutants with a short neuraminidase stalk. Infections in chickens, common quails, red-legged partridges and turkeys may select for mutants with human receptor specificity. Infection in Ratitae species may lead to the selection of PB2-E627K and PB2-D701N mutants and the conversion of nH7N9 to a highly pathogenic avian influenza virus.
authors.affiliation: Department of Intensive Care, Queen Elizabeth Hospital , Hong Kong, China.
authors.forename: Kang
authors.initials: K
authors.lastname: Yiu Lai
authors.affiliation: Department of Intensive Care, Queen Elizabeth Hospital , Hong Kong, China.
authors.forename: George
authors.initials: G
authors.lastname: Wing Yiu Ng
authors.affiliation: Department of Pathology, Queen Elizabeth Hospital , Hong Kong, China.
authors.forename: Kit
authors.initials: K
authors.lastname: Fai Wong
authors.affiliation: Department of Medicine, Queen Mary Hospital , Hong Kong, China.
authors.forename: Ivan
authors.initials: I
authors.lastname: Fan Ngai Hung
authors.affiliation: Department of Intensive Care, Queen Elizabeth Hospital , Hong Kong, China.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Kam Fai Hong
authors.affiliation: Department of Medicine, Queen Elizabeth Hospital , Hong Kong, China.
authors.forename: Fanny
authors.initials: F
authors.lastname: Fan Cheng
authors.affiliation: Department of Pathology, Queen Elizabeth Hospital , Hong Kong, China.
authors.forename: John
authors.initials: J
authors.lastname: Kwok Cheung Chan
keywords: H7N9; H9N2; PB2 protein; poultry markets; quail