Further Studies of the Antigenic Properties of H3N2 Strains of Influenza A Isolated from Swine in South East Asia

Abstract
H3N2 strains of influenza A isolated from swine in Hong Kong were compared with human strains of H3N2 influenza A variants in reciprocal HI [hemagglutination inhibition] tests using ferret sera. One isolate from swine was indistinguishable from A/Hong Kong/68, 1 set of viruses isolated in 1976 and 1977 was most related to A/Hong Kong/68 but was not identical to it, 2 isolates from 1976 were bridging strains that cross-reacted equally with the contemporary variants A/Victoria/3/75 and A/Texas/1/77, similarly to a small number of recent human isolates, and 2 isolates from 1977 were similar to A/Victoria/3/75. These general relationships were supported by neuraminidase inhibition tests. The findings confirm and extend previous results indicating that swine may be a reservoir of old and novel variants of influenza A H3N2 strains related to those that infect Man.