Studies in swine of Asian influenza virus.

This article reports on experiments with 6- to 8-week-old pigs infected with a human isolate of Asian strain influenza virus and on the successful passage of this virus into a second group of pigs. These findings are discussed in relationship to negative results obtained by others when swine sera, collected from apparently healthy animals before and after the recent Asian influenza epidemic, were tested for the presence of complement-fixing and haemagglutination-inhibiting antibodies.Six "normal" pigs were inoculated intranasally with 1.0 ml of fluid containing approximately 3 200 000 EID(50) of Asian influenza virus. Clinical evidence of disease was not apparent, but Asian strain virus was isolated from four of the pigs and the development of haemagglutination-inhibiting antibody to A/Asia/Japan/305/57 antigen was detected in all of them. Virus isolated from the first group was inoculated intranasally into another group of six "normal" pigs. Clinical evidence of illness was also absent in this group, but Asian strain virus was isolated from five pigs. Haemagglutination-inhibiting antibody developed in all six pigs but complement-fixing antibody in none.The authors conclude that the available evidence indicates that swine did not play a significant role in the epidemiology of the Asian influenza epidemic in the USA, and that the Asian strain appears not to have established itself in swine.