Lesions in aborted bovine fetuses and placenta associated with bovine viral diarrhoea virus infection.

Abortions in dairy cattle were investigated on 55 dairy farms sited in North West England, using a multi-level diagnostic technique. After pathological examination of fetal and placental tissues collected at the time of abortion, possible causes for these abortions could be identified, supported by bacteriological and serological laboratory findings. Of 150 abortions investigated, Bovine Viral Diarrhoea (BVD) virus infection was related to 40 episodes (27% of the total), often accompanied by evidence of concurrent infections. Lesions associated with BVD abortions were found in fetal eyelid, lung, and occasionally myocardium. Lesions in the lung were most consistent, characterized by mononuclear inflammatory cell infiltration of peribronchiolar and inter-alveolar tissues. Placental lesions were non-specific. It is concluded that the lesions observed are insufficient to be the primary cause of abortion. However, the pathological changes associated with BVD infection in the placenta may allow secondary opportunist pathogens to cross the feto-maternal barrier, thereby threatening the health of the fetus and the physiological and endocrinological functions of the placenta which maintain pregnancy.