ANALYSES OF RESTRICTION FRAGMENT PATTERNS (RFPS) AND PATHOGENICITY INBABY MICE OF EQUINE-HERPESVIRUS-1 AND EQUINE-HERPESVIRUS-4 (EHV-1 ANDEHV-4) STRAINS CIRCULATING IN DANISH HORSES

Twentyfive strains of equine herpesvirus 1 (EHV-1) and one strain of e quine herpesvirus 4 (ERV-4) isolated from material from various clinic al cases in Denmark, together with reference EHV-1 and EHV-4 strains, were compared by restriction fragment pattern (RFP) analysis and inocu lation of baby mice. The RFP analyses revealed that all EHV-1 strains belonged to genome type Ip. Four fetal isolates exhibited genomic char acteristics that have been suggested as specific markers of the attenu ated strain Rac H, widely used as a live vaccine. As the use of live v accines against EHV-1 and EHV-4 has never been allowed in Denmark, it is assumed that Rac H derivatives have been acquired from visiting hor ses and thus are now circulating in the horse population. Baby mice in oculation revealed that four biotypes could be distinguished on the ba sis of pathogenicity. However, no strict correlation with pathogenicit y in the natural host was seen.