Persistence of Q strain of H2N2 influenza virus in avian species: antigenic, biological and genetic analysis of avian and human H2N2 viruses.

The characteristics of an avian influenza virus were compared in detail with those of human Asian (H2N2) influenza viruses. Antigenic analysis by different antisera against H2N2 viruses and monoclonal antibodies to both the hemagglutinin and neuraminidase antigens showed that an avian isolate, A/duck/München/9/79 contained hemagglutinin and neuraminidase subunits closely related to those of the early human H2N2 viruses which had been prevalent in 1957. However, this avian virus gave low HI titers with absorbed and non-absorbed antisera to different human H2N2 viruses isolated in 1957. Like human Q phase variant, such as A/RI/5-/57 (H2N2), hemagglutination of the above avian strain was not inhibited by the purified non-specific gamma-inhibitor from guinea pig serum. Growth behavior at restrictive temperature (42 degrees C) clearly differentiate the avian H2N2 virus from human influenza viruses, showing that the former virus grew well in MDCK cells at 42 degrees C but not the latters. Genomic analysis of these viruses revealed that the oligonucleotide map of H2N2 virus isolated from a duck was quite different from those of human H2N2 viruses from 1957 to 1967. The oligonucleotide mapping also indicated that different H2N2 influenza virus variants had co-circulated in humans in 1957.