Restriction endonuclease DNA fingerprinting of respiratory,foetal and perinatal foal isolates of equine herpesvirus type 1

DNA was prepared from 43 equine herpesvirus type 1 (EHV 1) isolates, 11 of which were from horses with respiratory disease, 22 from aborted equine foetuses, and 10 from foals that died perinatally. The restriction endonuclease DNA fingerprints of 10 of the 11 respiratory isolates, known with certainty to have been recovered from horses with respiratory disease, were entirely different from all but 3 of the 32 foetal or perinatal foal isolates. The exceptional respiratory isolate, EHV 1 Army 183, had a foetal (F) strain fingerprint but this virus cannot be said with certainty to have been isolated from the respiratory tract. The 3 exceptional foetal isolates, had respiratory (R) strain fingerprints, and were recovered from single sporadic abortions. There are no exceptions to the view that only R strains have been isolated from naturally occurring respiratory disease. Also it is clear that major epizootics of abortion (abortion storms) and of perinatal foal mortality are caused by F strains. The data together with an analysis of the epidemiological patterns, particularly in Australia, strongly support the view that F and R strains be regarded as separate species, EHV 1 and 4 respectively.