Avian influenza A viruses.

The antigenic structure of eight strains of influenza A viruses of avian origin was investigated by haemagglutination inhibition, virus neutralization and strain-specific complement fixation. All strains could be distinguished from each other, but certain cross-reactions were observed allowing the establishment of four antigenic groupings, as follows: (1) classic fowl plague virus ("Dutch" strain), Turkey/England/63 ("Langham" strain) and virus N; (2) two strains isolated from ducks, one in Czechoslovakia in 1956 and one in England in 1962; (3) a third strain isolated from ducks in England in 1956; (4) the "Smith" strain (Chicken/Scotland/59) and the tern virus (Tern/South Africa/61).This article also reports the results of tests to determine the capacity of the above-mentioned viruses to infect monkey-kidney cultures and to produce plaques in chick-embryo fibroblasts. It concludes with a discussion of problems connected with the classification and nomenclature of these viruses.