In vitro biological differences between the pathogenic and the apathogenic Marek's disease herpesvirus.

When three pathogenic and four apathogenic isolants of Marek's disease herpesvirus (MDHV) were compared, the pathogenic isolants differed from the apathogenic isolants in their in vitro growth and sensitivity to plaque inhibition by dextran sulfate. Plaques by the pathogenic MDHV isolants were distinctively different in their morphology from those by the apathogenic isolants, the plaque difference being most pronounced in chick embryo fibroblase (CEF) and duck embryo fibroblast (DEF) cell cultures. The pathogenic isolants formed plaques similarly in both CEF and DEF cultures, whereas the apathogenic isolants did so readily in CEF cultures, but very poorly in DEF cultures. The pathogenic isolants replicated better in DEF than in CEF cultures, whereas the apathogenic isolants replicated better in CEF than in DEF cultures. The sensitivitty to plaque inhibition by dextran sulfate was greater for the apathogenic isolants than for the pathogenic isolants of MDHV.