A retrospective serological survey of the encephalomyocarditis virus among pigs in Chiba prefecture, Japan.

One thousand two hundred and forty pigs' sera collected from 1975 to 1992 on 240 farms in Chiba prefecture were subjected to a neutralization test for the encephalomyocarditis (EMC) virus. Seven (23.3%) of 30 pigs in 1975 had neutralizing antibodies against the EMC virus. The antibody positive rates each year ranged from 16.7% (1976) to 56.3% (1981). The differences of antibody positive rates between districts were not great after 1985. These serological results suggested that the EMC virus infection had already been introduced by 1975 and that it is prevalent among pigs in Chiba prefecture.