Aetiologic study on an influenza-like epidemic in horses in China

About thirty thousands horses were affected and hundreds of them died in an epidemic caused by equine 2 influenza virus (H3N8) in China. The estimated morbidity and mortality accounted for 81% and 2%, respectively. The viral protein and RNA electrophoresis patterns revealed that the new isolates were antigenically different from the prototype strain influenza A/eq/Miami/1/63(H3N8). Therefore, the representative strain of the equine 2 subtype of influenza A virus recommended for producing reference reagents, vaccines, and for serological diagnosis must have been altered by antigenic drift.