Amino Acid Sequences of Haemagglutinins of Influenza Viruses of the H3 Subtype Isolated from Horses

The amino acid sequence of the haemagglutinin of A/equine/Miami/63 (H₃N₈), the prototype influenza virus of the H₃ subtype from horses, is deduced from the nucleotide sequence of virus RNA and compared with the sequences of haemagglutinins of viruses of this subtype isolated from humans [X-31 (H₃N₂)] and from birds [A/duck/Ukraine/63 (H₃N₈)] and with the sequence of the haemagglutinin of A/equine/Fontainebleau/79 (H₃N₈) a virus isolated from a recent outbreak of equine influenza. The amino acid sequence differences detected are discussed with reference to the structure of the molecules, their antigenicity and antigenic drift in influenza viruses isolated from horses.