Infection of pregnant sheep with the NADL strain of bovine virus diarrhoea virus and their subsequent challenge with Border disease IIB pool

Abstract

Ten South Country Cheviot ewes were injected intraperitoneally with NADL strain of bovine virus diarrhoea virus (BVD) on the 54th gestational day. At term, one produced a weak hairy lamb with generalized hypomyelinogenesis of the CNS-features characteristic of Border disease (BD) 3 produced non-hairy, normally myelinated offspring with severe intracranial malformations, one aborted and one produced an apparently normal lamb. Four ewes were killed at intermediate stages of gestation and some of the foetuses and placentae had lesions consistent with BD or the early phases of intracranial malformation. The following year the surviving 6 ewes were challenged with a pool of BD infected lamb brain; one produced a BD affected lamb, one a lamb with severe neural and skeletal malformations and one aborted. The other 3 produced normal offspring. The findings emphasize the close similarity between BVD and BD virus diseases and the variable extent of cross immunity between strains. It is suggested that the outcome of infection with these viruses is dependent upon genetic make-up and immune status of the dam and the strain of infecting virus in addition to the gestational age at infection.