Emergence and development of H7N9 influenza viruses in China

• Published in: Current opinion in virology Vol. 16; pp. 106 - 113
• Main Authors: Zhu, Huachen, Lam, Tommy Tsan-Yuk, Smith, David Keith, Guan, Yi
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.02.2016
• Subjects: Animals; Chickens; China - epidemiology; Communicable Diseases, Emerging; Ducks; Evolution, Molecular; Genotype; Humans; Influenza A Virus, H7N9 Subtype - classification; Influenza A Virus, H7N9 Subtype - genetics; Influenza A Virus, H7N9 Subtype - isolation & purification; Influenza in Birds - epidemiology; Influenza in Birds - transmission; Influenza in Birds - virology; Influenza, Human - epidemiology; Influenza, Human - transmission; Influenza, Human - virology; Phylogeny; Reassortant Viruses; Risk Factors
• ISSN: 1879-6257; 1879-6265; 1879-6265
• DOI: 10.1016/j.coviro.2016.01.020

•H7N9 virus was generated through sequential reassortments in ducks and chickens.•This virus originated from eastern China and has spread to over 20 provinces.•Regionally distinct lineages have been established with different genotypes.•Viruses present at live poultry markets fueled the recurrence of human infections.•Chickens served as the source of human infections in each outbreak wave. The occurrence of human infections with avian H7N9 viruses since 2013 demonstrates the continuing pandemic threat posed by the current influenza ecosystem in China. Influenza surveillance and phylogenetic analyses showed that these viruses were generated by multiple interspecies transmissions and reassortments among the viruses resident in domestic ducks and the H9N2 viruses enzootic in chickens. A large population of domestic ducks hosting diverse influenza viruses provided the precondition for these events to occur, while acquiring internal genes from enzootic H9N2 influenza viruses in chickens promoted the spread of these viruses. Human infections effectively act as sentinels, reflecting the intensity of the activity of these viruses in poultry.