RECENT H3N2 SWINE INFLUENZA-VIRUS WITH HEMAGGLUTININ AND NUCLEOPROTEIN GENES SIMILAR TO 1975 HUMAN STRAINS

Of the four pandemic strains of human influenza A virus observed this century, the 1977 virus strain was very similar in all genes to a 1950 isolate. Since mammalian influenza A viruses change annually by genet ic drift, this reappearance could only be attributed at that time to c onservation of the virus in a frozen state. We report here the isolati on of swine influenza A viruses with haemagglutinin and nucleoprotein genes which are virtually identical to those of the human virus that c irculated in 1975. We have also found serological evidence that this v irus is circulating extensively in Quebec swine herds. We propose that human-like H3N2 influenza A strains may remain invariant for long per iods in swine, which may serve as a reservoir for human pandemics.