Direct sequencing of the HA gene of clinical equine H3N8 influenza virus and comparison with laboratory derived viruses.

Equine influenza viruses propagated in the laboratory in alternate hosts such as embryonated hens' eggs or mammalian cell culture have been analysed by HA sequencing and antigenically and their sequence compared to the original virus present in clinical material. In contrast to clinically derived human influenza virus which generally grows in MDCK cells without change, the data for equine influenza virus were less clear in that variants of equine virus were derived in both eggs and cells. The study indicated that the current use of eggs for equine influenza virus surveillance and vaccine production is entirely appropriate, but that care should be exercised when equine influenza vaccines are produced in eggs or on mammalian cell cultures.