Alterations in the equine herpesvirus 1 genome after in vitro and in vivo virus passage.

The effect of in vitro and in vivo serial virus passage on the genetic stability of equine herpesvirus 1 (EHV-1) was investigated by restriction endonuclease analysis of the viral DNA. DNAs of EHV-1 isolates at different passage levels in cultured cells or in Syrian hamsters were compared by electrophoresis of the DNA cleavage fragments produced by restriction endonuclease digestion. No changes were observed in the restriction profile of the DNAs of EHV-1 strains after 100 sequential passages in cultured equine cells. However, serial passage of the virus in hamsters or in cells of non-equine origin quickly gave rise to alterations in the viral DNA. These changes occurring in the restriction endonuclease profiles of EHV-1 DNA during serial virus passage in non-equine cells or animals hosts could be explained by sequence additions or deletions to preexisting restriction fragments resulting in variation in their electrophoretic mobilities.