Abstract
After the emergence of H7N9 avian influenza viruses (AIV) in early 2013 in China, active surveillance of AIVs in migratory birds was undertaken, and two H7N7 strains were subsequently recovered from the fresh droppings of migratory birds; the strains were from different hosts and sampling sites. Phylogenetic and sequence similarity network analyses indicated that several genes of the two H7N7 viruses were closely related to those in AIVs circulating in domestic poultry, although different gene segments were implicated in the two isolates. This strongly suggested that genes from viruses infecting migratory birds have been introduced into poultry-infecting strains. A Bayesian phylogenetic reconstruction of all eight segments implied that multiple reassortments have occurred in the evolution of these viruses, particularly during late 2011 and early 2014. Antigenic analysis using a hemagglutination inhibition test showed that the two H7N7 viruses were moderately cross-reactive with H7N9-specific anti-serum. The ability of the two H7N7 viruses to remain infectious under various pH and temperature conditions was evaluated, and the viruses persisted the longest at near-neutral pH and in cold temperatures. Animal infection experiments showed that the viruses were avirulent to mice and could not be recovered from any organs. Our results indicate that low pathogenic, divergent H7N7 viruses circulate within the East Asian-Australasian flyway. Virus dispersal between migratory birds and domestic poultry may increase the risk of the emergence of novel unprecedented strains.
Highlights
Introduction The circulation ofH7 subtype avian influenza viruses (AIV) in poultry has caused outbreaks in poultry and has even resulted in human infection for decades
Active surveillance for AIVs in migratory waterfowl was undertaken in the Chenhu and Honghu wetlands—two major overwintering and stopover sites in Hubei Province that are located on the East Asian-Australasian flyway (Fig. 1)
A BLAST search showed that several genes of HH179/H7N7 and CH1228/ H7N7 were highly homologous (>99%) with various virus strains isolated from domestic poultry in China, indicating that gene flow occurs between wild birds and domestic poultry
Summary
H7 subtype avian influenza viruses (AIV) in poultry has caused outbreaks in poultry and has even resulted in human infection for decades. In 2003, outbreaks of HPAI H7N7 struck poultry in several European countries, and 86 poultry workers and three of their family members were infected with this subtype in the Netherlands[4]. Among these infections, almost all infected persons developed mild to moderate conjunctivitis, and one person died from pneumonia and acute respiratory distress syndrome[4]. The virus responsible was a novel reassortant strain between wild bird-origin H7 and N9 viruses and poultry-infecting H9N2 viruses[7, 8]
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