EVIDENCE FOR INTERSPECIES TRANSMISSION AND REASSORTMENT OF INFLUENZA-A VIRUSES IN PIGS IN SOUTHERN CHINA

The Asian/57, Hong Kong/68, and Russian/77 pandemics of this century a ppeared or reappeared in China. Interspecies transmission and genetic reassortment of influenza viruses have been implicated in the origin o f these human pandemic influenza viruses. Pigs have been suspected to be the ''mixing vessel'' where reassortment occurs. To investigate thi s possibility, 104 porcine influenza viruses collected at random from southern China from 1976 to 1982, including 32 H3N2 isolates and 72 H1 N1 isolates, were studied using dot blot hybridization, partial sequen cing, and phylogenetic analysis. There were 29 of 32 H3N2 isolates cha racteristic of viruses originally derived from humans; the other 3 iso lates were reassortants containing genes from porcine and human influe nza viruses. Phylogenetic analyses of the polymerase B1 (PB1) genes sh owed that interspecies transmission from humans to pigs has happened m ultiple times in pigs in Southern China. All 72 H1N1 isolates were of porcine origin characteristic of classical porcine H1N1 influenza viru s. Analysis of 624 genes of porcine influenza viruses from Southern Ch ina failed to detect any evidence for avian influenza virus genes. Thi s contrasts to what is currently found in Europe, where the majority o f porcine influenza virus isolates are of avian origin. (C) 1994 Acade mic Press, Inc.