Further isolation of a recombinant virus (H1N2, formerly Hsw1N2) from a pig in Japan in 1980.

In September 1980, an outbreak of febrile respiratory disease was observed in a herd of sows (1-2 years of age) in Ehime Prefecture, Japan. Most of the swine showed clinical signs of disease such as depression, anorexia, fever, nasal discharge, and cough. A hemagglutinating agent was isolated from a nasal swab from one of the diseased pigs. By cross-hemagglutination-inhibition and neuraminidase-inhibition tests with antisera to influenza viruses of swine origin, the isolate was identified as an influenza A virus of the H1N2 (former designation, Hsw1N2) subtype, and designated A/swine/Ehime/1/80 (H1N2). Significant antibody rises against the surface antigens of the isolate were found in convalescent swine sera. The distribution of antibody against H1N2 virus in swine sera in Ehime Prefecture was examined. Seven (8%) of 93 sera collected after the outbreak (in 1981) showed antibodies to only H1 and N2 antigens but none of the sera before the outbreak contained such antibodies, indicating that H1N2 virus had been restricted prevalent among swine but was not wide-spread until 1981.