Isolation of herpesvirus from equine leukocytes: comparison with equine rhinopneumonitis virus.

An agent which possessed the properties of herpesviruses was isolated from the leukocytes of 71 out of 80 (88.7%) apparently normal Iowa horses. It was ether- and heat-sensitive, DNA type, and produced type-A intranuclear inclusion bodies in cell cultures. Electron micrographs revealed a virion of typical herpesvirus structure. Leukocyte isolate virus could be differentiated from equine rhinopneumonitis virus (ERV) by serum neutralization, by growth differences in rabbit kidney cells, and by fluorescent antibody staining. Specific neutralizing antibody against this agent was found in a pooled serum sample from normal horses and in the serums of herpesvirus carrier horses. Serum from a mare inhibited growth of both ERV and leukocyte viral isolates. Normal sheep, calf, and rabbit serum did not neutralize either virus.