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

Abstract

SUMMARYThe 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 (H3Ns)] 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.

Antigenic and genetic evolution of equine H3N8 influenza A viruses

“…This is in accordance with previous observations (Daniels et al, 1985 ;Oxburgh et al, 1993Oxburgh et al, , 1994. There are also more sequential changes in antigenic site B than any other site suggesting that antigenic site B is under greater selective pressure; such an observation is not surprising when it is considered that antigenic site B is located on the tip of the HA molecule.…”

“…The antigenicity of the HA of the human H3 influenza A virus subtype has been studied in detail, and the locations of five major antibody binding sites (A to E) have been proposed (reviewed by Wiley & Skehel, 1987). The antibody binding sites of equine H3 HA have not been completely mapped, but as it is believed that human and equine H3 influenza viruses share a common ancestry (Daniels et al, 1985), it is thought that the antigenic sites of the equine H3 HA1 may be equivalent to those proposed for human H3.…”

Recent evolution of equine influenza and the origin of canine influenza

“…Sequence data for equine virus HAs indicate the evolution of four distinct lineages. The first was associated with antigenic drift, between 1963 and 1980 (6,7,9), and following this three separate branches formed a "Eurasian" lineage, an "American" lineage, and a divided lineage containing two clades, "Florida" clade 1 and Florida clade 2 (10,11). The HAs of the canine viruses are most similar to those of Florida clade 1 equines.…”

“…Genetic comparisons indicate that the canine viruses are closely related to equine viruses that were in circulation in horses around 2000 (3,5). In studies of differences in equine viruses isolated since 1963 (6)(7)(8) and between equine and canine viruses (3,5), the sequences of genes for the hemagglutinin membrane glycoprotein (HA) have been compared. Sequence data for equine virus HAs indicate the evolution of four distinct lineages.…”

Evolution and Ecology of Influenza A Viruses

“…The HA of the prototype human H3 virus, AlAichi/2/68, is more closely related to that of avian H3 viruses than to that of equine H3 viruses (33,39,86 (30).…”