Evidence for evolutionary stasis and genetic drift by genetic analysis of two equine influenza H3 viruses isolated in France

The amino acid sequences of the HA(1) portion of the haemagglutinin of two equine A(H3N8) influenza viruses isolated in France in 1993 and 1998 were a nalysed to determine their evolutionary relationship with 51 other HA(1) am ino acid sequences available in databanks, Our data show that the French st rain isolated in 1993 belongs to a group of phylogenetically related viruse s branched on the main trunk, illustrating the main lineage of evolution of the equine-2 H3 sequences before its split into two distinct lineages in t he late 1980s. By contrast, the 1998 French isolate appears to belong to th e more recent 'Eurasian' lineage. These data suggest that equine-2 strains antigenically related to old prototype viruses may cocirculate with the mor e recent 'Eurasian' and 'American' lineages, In conclusion, it may be neces sary to include both strains representative of recent equine influenza vari ants and an older prototype strain in the current equine influenza vaccines . (C) 2000 Published by Elsevier Science B.V. All rights reserved.