Natural history of influenza in swine in Hawaii: prevalence of infection with A/Hong Kong/68 (H3N2) subtype virus and its variants, 1974-1977

From September 1974 to January 1978, about 25% of 254 swine farms, studied on four of six Hawaiian islands, had swine with antibody to A/Hong Kong/68 (H3N2) subtype of influenza virus. Of 290 swine 2 to 5 years of age in a single herd, 72% had antibody. Antibody titers were consistently higher to A/England/42/72 and A/Port Chalmers/1/73 antigens than to A/Victoria/3/75 or A/Hong Kong/1/68 antigen. Few swine had antibody to the A/Hong Kong/68 antigen. Antibodies to H3N2 and Hsw1N1 subtype of virus persisted at high titer in the same animals for more than 3 years; however, titers to the Hsw1N1 subtype were considerably higher. The occurrence of H3N2 infection in swine appeared shortly after the occurrence of the same H3N2 variant in human population. To date there is no evidence that the H3N2 subtype has become established in swine in Hawaii.