Isolation and characterization of influenza A viruses from avian species in Hong Kong

Surveillance of apparently healthy ducks, chickens, and geese at a poultry dressing plant in Hong Kong yielded 51 haemagglutinating viruses 25 of which were influenza A viruses. Of these, 24 were subtyped into 13 combinations based on haemagglutinin and neuraminidase surface antigens. Of the 13 different influenza A viruses isolated, 7 possessed combinations of haemagglutinin and neuraminidase subunits that have not been reported previously-i.e., Hav2N1, Hav2Nav5, Hav4N2, Hav7N2, Hav7Nav1, Hav7Nav3, and Hav7Nav6. Four of the isolates were non-avid: they were not neutralized by antisera to any of the reference subtypes of influenza A viruses, yet antisera to each isolate inhibited both that virus and a known reference strain. The large number of combinations of haemagglutinin and neuraminidase and the isolation of two different influenza A viruses from one duck suggests that recombination may be occurring in nature.