Sero-epizootiological study on swine influenza in a prefecture of Japan.

A total of 1799 swine sera collected in Toyama prefecture in the central part of Japan during the years 1978-82 were tested for antibody against swine influenza virus (SIV), A/New Jersey/8/76 (H1N1). A high prevalence of antibody was observed in the years after the severe epizootic of SI, 34.5% in 1979 and 51.7% in 1982. In other years, the percentages of positive sera were low and ranged from 1.7 to 12.4%. Regional variations were seen in relation to a small scale epizootic. No antibody to SIV was detected in any of the sera collected during the warm season. In the following dry and cold winter, however, a severe epizootic occurred among the swine populations.