Pathogenicity for the Sheep Foetus of Bovine Virus Diarrhoea-Mucosal Disease Virus of Bovine Origin

SUMMARY Thirty pregnant, BVD antibody-free Dorset Horn ewes were divided into three equal groups and infected experimentally with a mixture of 10 strains of BVD virus isolated from cattle in Britain. Ewes of groups I and II were inoculated intramuscularly at day 25 to 40 of gestation with a high and low dose of virus respectively. Ewes of group III received inoculum partially inactivated by heat. Ten additional pregnant ewes served as uninoculated controls. None of the inoculated ewes showed any evidence of malaise, but all had seroconverted within 42 days. Of the 30 infected ewes 13 aborted and 12 were found ‘empty’ when killed 133 or 170 days after the presumed dates of conception. Four ewes produced five full-term lambs of which only two were bom alive, and both showed clinical signs characteristic of Border disease (‘hairy shakers’). One ewe was carrying two foetuses, one mummified and one alive when killed at 131 days of gestation. There was no significant difference in terms of foetal morbidity between the three infected groups. AH foetuses and lambs from infected dams showed moderate to severe growth retardation; in two foetuses and five lambs there were lesions of hypomyelinogenesis congenita; and one lamb showed cerebellar hypoplasia. It is concluded that some British strains of BVD (a) are highly pathogenic for the sheep foetus, (b) interfere with normal development of the foetus leading to growth retardation and (c) are capable of producing Border disease (hypomyelinogenesis congenita) and cerebellar hypoplasia. Possible practical implications of the findings are discussed.