Comparison of four horse herpesviruses.

Four equine herpesviruses (equine abortion virus, equine herpesvirus types 2 and 3, and equine cytomegalovirus) were compared. The equine abortion virus did not cross-neutralize with any of the other viruses, but the other three did show varying degrees of cross-neutralization among themselves. Equine abortion virus grew more quickly in tissue cultures than did the others, and attained higher titers of infectivity in the culture fluid; it also formed plaques in a wider range of tissue culture species, although the other three were not specific for one tissue culture system only, in that they would multiply in rabbit and cat kidney cultures. The densities of the deoxyribonucleic acids of all four viruses were in the range 1.716 to 1.717 g/ml (a guanine plus cytosine content of 57 to 58%). Taxonomic separation, as a distinct serotype, of equine abortion virus from the other herpesviruses seems to be justified. The other three are closely related to one another. They should perhaps be regarded as separate viruses and termed horse herpesviruses types 2, 3, and 4, although an alternative view would be to regard them as variants of a single virus type. The question of whether types 2, 3, and 4, or any other herpesviruses, should be placed in a phylogenetically distinct subgroup, known as cytomegaloviruses, is a moot point.