Serological evidence of H1 influenza virus infection among Japanese hogs.

Classical H1 influenza firus infection among Japanese hogs was confirmed in 1978 by serological examination. Of 820 swine sera collected from July 1977 to February 1979 in Miyagi Prefecture, northern Japan, six sera were found to contain haemagglutination inhibition (HI) antibodies to the A/FM/1/47 (H1N1) strain. Of the six sera, one showed a significant high HI antibody titre, which was classified as IgM, to the FM1 strain, but not the other H1N1 variants. These results strongly suggest that hogs may carry an old type of H1 influenza virus. The possible role of pigs as a reservoir of human pandemic influenza strains is discussed.