Border disease: effect of virus administered intracerebrally to newborn lambs

Six BVD antibody-free Dorset Horn lambs, less than 3-days-old, were infected by intracerebral inoculation of BD virus. Three of these lambs (Group I) were killed 7 days after inoculation (p.i.) and 3 (Group II) 21 days p.i. None of the lambs showed clinical signs of disease. Of the 5 lambs in which infection was established, 3 of Group I and 2 of Group II showed lesions of non-suppurative encephalitis. Although of varying severity and extent in individual animals, the lesions in all lambs appeared to be primarily of the same nature, with the cerebral white matter being the main target. BD virus was isolated from all lambs of Group I, killed 7 days p.i., but from none of Group II, killed 21 days p.i. Thus the induced BD infection appeared to be of a transient nature. The results indicate that the CNS of newborn lambs is capable of supporting BD virus replication with subsequent development of lesions. It is suggested that some of the cases of non-suppurative encephalitis of obscure aetiology occasionally encountered in young lambs in the field may be the result of infection with BD virus.