In vitro characterisation of high and low virulence isolates of equine herpesvirus-1 and -4.

Basic in vitro characteristics of high and low virulence isolates of equine herpesviruses-1 and -4 were investigated with particular reference made to the Ab4 and V592 isolates of EHV-1 as both have distinct endotheliotropism and clinical outcomes in pony challenge studies. Additionally, some EHV-4 isolates that showed variations in clinical outcome were included in some experiments. The aim of the study was to identify an in vitro characteristic that would differentiate strains of known virulence. Such a system could then be applied to vaccine and virulence studies as an effective screening tool. Viral growth kinetics in a variety of cell culture systems, plaque size, ability to replicate in fetal endothelium in organ culture, and sensitivity to acyclovir were compared. No reliable marker system that differentiated between higher and lower virulence isolates of EHV-1 and EHV-4 was identified.