Continued circulation of reassortant H1N2 influenza viruses in pigs in Japan.

In 1991 and 1992, H1N2 influenza A viruses were isolated from the lungs of pigs with overt signs of respiratory disease at farms in the Chiba and Kanagawa prefectures of Japan. To determine the genetic origin of these isolates, we phylogenetically analyzed partial nucleotide sequences of their genes. The results indicate that influenza viruses possessing the N2 of human influenza virus and seven other gene segments of classical H1N1 swine influenza virus, which were first isolated in 1980, have become established in Japanese pigs.