A strain of influenza A H9N2 virus repeatedly isolated from human population in China.

OBJECTIVE

To understand the subtype of surface proteins (hemagglutinin and neuraminidase) and antigenic character of the isolate of influenza virus, as well as to know its origin.

METHODS

The virus isolation was performed on MDCK cells. The identification and antigenic analysis of the isolate were carried out with HI and NI tests. The serum antibody in population against the isolate was detected with HI and neutralization assays. The individual investigation of the patient from whom the H9N2 virus was isolated was followed.

RESULTS

The isolate was H9N2 subtype of influenza A virus. It was G9 like strain. Its antigenicity was different from that of H9N2 viruses which were previously found in humans, chickens and pigeons. The HI and neutralization titers to H9N2 virus in convalescent serum of the patient reached 1:400 and > or =1: 640, respectively. The HI antibody titer 1:25 to H9N2 virus was also detected in the serum of patient's mother.

CONCLUSIONS

The isolate is H9N2 subtype of influenza A virus and belongs to G9 like strain. The antigenic character of the isolate was different from that of H9N2 viruses found previously in humans, chickens and pigeons. The greatest possibility was that her mother had contacted with birds, especially chickens carrying H9N2 virus, then transmitted to her or she breathed in the air borne with H9N2 virus particles directly.