Equine Herpesviruses: Antigenic Relationships and Deoxyribonucleic Acid Densities

Equineherpesviruses witha deoxyribonucleic aciddensity of1.716to1.717 g/cm3 were compared withone another bytheplaque-reduction testandbythe rateofdevelopment ofcytopathic effect as indicated byplaque sizeinrabbit kidneycultures. Ofthe19isolates studied, the9 whichhadalready been tentatively labeled equine abortion viruses were serologically similar toone another; eachofthemgrew more quickly thandidany oftheother 10isolates although themean plaque sizes formed aseries ofgradations with no clear hiatus whichwouldpermit theunequivocal delineation oftheabortion viruses fromthe slowly growing strains. The10slowly growing isolates showed antigenic heterogeneity even thoughcomplement was present;theneutralizing capacity ofan antiserum against theheterologous strains was,inmostinstances, markedly less thanagainst thehomologous strains, therangeofthe50%endpoints being much greater thanthatobserved among theequine abortion viruses, or among isolates ofherpes simplex type1.There was no crossneutralization between theequine abortion viruses andany ofthe10slowly growing isolates. An extrabandof deoxyribonucleic acid, at1.723 to1.725g/cm3, was present intwooftheslowly growingstrains whenoriginally grown inrabbit cells, butwas no longer present after passageincatcells. Thisbandoccupied thesame position asone reported in thehamster-passaged strain ofequine abortion virus, andhada density similar tothatoftheequine genital herpesvirus. Although thetaxonomic demarcation of theequine abortion viruses andtheslowly growing herpesviruses fromone another isstill open toquestion, theycan beconveniently labeled equine herpesviruses 1and2,respectively; thegenital virus wouldbetermedequine herpesvirus 3.