Twentyfive strains of equine herpesvirus 1 (EHV-1) and one strain of equine herpesvirus 4 (ERV-4) isolated from material from various clinical cases in Denmark, together with reference EHV-1 and EHV-4 strains, were compared by restriction fragment pattern (RFP) analysis and inoculation of baby mice. The RFP analyses revealed that all EHV-1 strains belonged to genome type Ip. Four fetal isolates exhibited genomic characteristics that have been suggested as specific markers of the attenuated strain Rac H, widely used as a live vaccine. As the use of live vaccines against EHV-1 and EHV-4 has never been allowed in Denmark, it is assumed that Rac H derivatives have been acquired from visiting horses and thus are now circulating in the horse population. Baby mice inoculation revealed that four biotypes could be distinguished on the basis of pathogenicity. However, no strict correlation with pathogenicity in the natural host was seen.
- Equine herpesvirus
- Restriction fragment pattern analysis