Properties of the Hong Kong influenza virus. I. General characteristics of the Hong Kong virus.

Biological properties of the Hong Kong influenza variants are described in relation to the isolation and identification of strains, sensitivity to nonspecific inhibitors, and serological diagnosis. Hong Kong virus strains were readily isolated in both eggs and monkey-kidney tissue cultures and were identified by haemagglutination-inhibition (HI) with chicken erythrocytes. The morphology, soluble antigen, and neuraminidase of Hong Kong isolates were similar to those of earlier A2 Asian influenza strains. Hong Kong haemagglutinins were related in varying degrees to previous human A2 and animal influenza viruses.The sensitivity of Hong Kong isolates to nonspecific haemagglutination inhibitors in serum varied widely. From least to most inhibitory, the ranking of sera of 8 animal species tested was: monkey, goat, chicken, human, rabbit, ferret, guinea-pig and horse. The same sera were treated with heat, trypsin, periodate, receptor-destroying enzyme and kaolin to determine the most effective way of removing nonspecific inhibitors. The results varied with the animal species involved.The A2 Asian antigen was nearly as effective as Hong Kong antigen in detecting antibody rises by HI tests. HI tests with either antigen were more efficient than complement-fixation tests for serodiagnosis of Hong Kong influenza, but for maximum efficiency both tests were required.