[Antigenic drift of a strain of influenza equi virus isolated in France during the winter of 1978-1979].

A strain of Influenza Equi virus isolated during winter 1978-1979 has been compared with Influenza A/Equine/Miami/1/63 (H3N8) strain by cross reactions performed by radial haemolysis (RH) and hemagglutination inhibition (HAI) test. Specific antisera were prepared on hens and guinea-pigs. Results differed according to the species on which the sera were prepared and the two methods of titration of the antibodies. Hens sera were unable to differenciate by HAI the newly-isolated strain Influenza A/Equine/Joinville/1/78 from the Influenza A/Equine/Miami/1/63 (H3N8) strain, but an antigenic drift of Influenza A/Joinville/1/78 from the original Influenza A/Equine/Miami/1/63 virus could be demonstrated with guinea-pigs' sera either by HAI or by RH. By HAI, Influenza A/Equine/Joinville/1/78 virus seemed dominant over Influenza A/Equine/Miami/1/63 (H3N8) virus, while in opposite Influenza A/Equine/Miami/1/63 (H3N8) seemed dominant over Influenza A/Equine/Joinville/1/78 when the viruses were compared by RH. Thus, antigenic sites and correspondant antibodies involved in HAI and RH reactions appeared at least partially differents.