Diaplacental infections with ruminant pestiviruses.

Pestiviruses are capable of causing diaplacental infections. Maternal viremias are important for localizing virus in the ruminant placentome. Placental lesions occur with cytopathic BVDV and noncytopathic BDV. The ruminant fetus is very susceptible to pestivirus infections once the virus crosses the placenta because the fetus is 1) agammaglobulinemic, 2) immunologically immature, and 3) it has many immature organ systems with undifferentiated cells. Cytopathic BVDV (NADL) in calves and noncytopathic BDV (BD-31) in lambs cause a variety of clinical syndromes including early embryonic death, abortion, stillbirth, malformed fetuses, and/or low birth weight with viral persistence and immunological tolerance. The cytopathic BVDV (NADL) reviewed herein caused pulmonary, placental and dermal lesions when infection occurred at 80-90 days gestation. In contrast, infection at 140-150 days resulted in retinal dysplasia and cerebellar hypoplasia. The lesions were attributed to direct viral cytopathology. Noncytopathic BDV (BD-31) in lambs caused weak lambs, with hairy fleece and tonic-clonic tremors. The lambs were of low birth weight, persistently viremic and immunologically tolerant. The lambs are hypothyroid and had severe hypomyelination. It is hypothesized that the central lesion leading to many of the neural, skeletal and dermal lesions was the endocrine dysfunction leading to hypothyroidism.