BVD and bovine viral abortions

[Symposium: Clinical Aspects of Bovine Viral Diseases]

Abstract

At our present state of knowledge, virus diseases contribute only a small percentage to the whole enigma of bovine abortion. Research and increased capabilities of diagnostic laboratories are gradually providing information on the role of viruses as abortifacients. Diagnostic laboratories emphasize the role of infectious diseases in abortion when in fact the problem may be multifaceted. Isolation of a virus from an aborted fetus does not necessarily incriminate the virus as the primary etiological agent. The infection in the fetus may be too mild by itself to cause abortion. However, certain viruses such as the BVD virus may enhance the replication of other coexisting viruses.
There appears to be a substantial barrier in the fetus to viruses from the external environment. In addition to Maternal immunity, which protects the fetus from natural infection, immunoglobulins start forming in the fetus at 90- 120 days of age. Prior to this time non-specific inhibitors may have a protective effect. Also, complement is formed within the first third of fetal life and its concentration increases steadily during the prenatal period. An early protective effect is provided by evidence that placental attachment (approx. 35 days) must occur before viruses can be transferred to the fetus.