Studies on relationships between human and porcine influenza. 1. Serological evidence of infection in swine in Great Britain with an influenza A virus antigenically like human Hong Kong-68 virus.

Serological evidence of infection of swine in Great Britain with an influenza A virus closely related to the human A/Hong Kong/68 (H3N2) variant was detected by a variety of serological tests. The Hong Kong/68 virus was first detected in man in Great Britain in August 1968 and was prevalent in the winters of 1968-69 and 1969-70. There was no evidence that swine had been infected with a Hong Kong/68-like virus before the appearance of the virus in man. The detection of virus-neutralizing antibody and high titres of neuraminidase-inhibiting antibody for Hong Kong/68 virus, and the production of precipitin lines corresponding to influenza A ribonucleoprotein and haemagglutinin and neuraminidase antigens of Hong Kong virus in immunodiffusion tests indicated that the swine sera contained antibody specific for the Hong Kong/68 virus. Evidence suggested that the infection of swine occurred in the early months of 1970. Clinical influenza among swine in Great Britain was not reported during the study period and there was no serological evidence of infection with "classical" swine influenzavirus strains.