EFFECT OF INFLUENZA A EQUINE/H3N8 VIRUS ISOLATE VARIATION ON THE MEASUREMENT OF EQUINE ANTIBODY-RESPONSES/

This study has tested the effect of using homologous or heterologous e quine influenza A virus isolates to evaluate serum antibody levels to influenza A virus in vaccinated and naturally-infected horses. In addi tion, the potential effect of antigenic selection of virus variants in egg versus tissue culture propagation systems was studied. Serum anti body levels in samples from horses recently infected with a local infl uenza A virus isolate (A/equine 2/Saskatoon/1/90) or recently vaccinat ed with a prototype isolate (A/equine 2/Miami/1/63) were assessed by h emagglutination inhibition and by single radial hemolysis using cell o r egg-propagated A/equine 2/Saskatoon/1/90, A/equine 2/Miami/1/63 or A /equine 2/Fontainebleau/1/79. There were no significant differences in hemagglutination inhibition or single radial hemolysis antibody level s obtained with homologous or heterologous isolates or between viruses propagated in either eggs or cell culture. However there was a trend to higher titers in the hemagglutination inhibition assay when cell-pr opagated virus was used. These results suggest that antigenic variatio n in equine influenza A virus isolates and host-cell selection of anti genic variants during virus propagation may not be of sufficient magni tude to influence serological evaluation of antibody responses by hema gglutination inhibition or single radial hemolysis.