Influenza viral infection of swine in the United States 1988–1989

Summary Swine are an animal reservoir for influenza viruses capable of causing disease in humans. A serological survey in 1988–1989 demonstrates that subtype H1 influenza viruses continue to circulate at high frequency among swine in the north-central U.S.A. (average 51% incidence). Subtype H3 viruses antigenically similar to current human H3 viruses are circulating at low frequency (average 1.1%), particularly in the southeast U.S.A.