Human influenza A viruses in pigs: isolation of a H3N2 strain antigenically related to A/England/42/72 and evidence for continuous circulation of human viruses in the pig population.

An influenza virus strain isolated in Northern Italy in 1977 was identified as belonging to the H3N2 subtype (A/swine/Italy/1850/77). A close antigenic relationship to the human strain A/England/42/72 was demonstrated. Serologic surveys of 548 pig sera from 53 farms in two provinces in Northern Italy demonstrated the existence of antibodies to the swine/Italy/1850/77 strain and to A/Hong Kong/1/68, A/Victoria/3/75 and H 1 N 1 (Hsw 1 N 1) strains in the pig population.