In case #1, veterinarians observed uncommon BVDV presentations such as these tongue lesions. If you ask a practitioner to describe a “typical” outbreak of bovine viral diarrhea (BVD) you might get a variety of answers. In fact, the more experience one has with BVD the less willing one might be to give a definitive answer. The clinical manifestations that are lumped under the term BVD are many and varied and include respiratory, reproductive and enteric disease. Multiple “forms” of BVD are recognized. Among these are acute uncomplicated BVD, severe acute BVD (including hemorrhagic syndrome), acute BVD-respiratory disease, acute BVD-reproductive disease, persistent infection and mucosal disease. Many practitioners have a mental check list of clinical signs that would lead them to test for BVD and, conversely, a check list of signs that they would not associate with BVD. This article will discuss cases which, at first blush, “just didn’t look like BVD.”
The collection of disease syndromes referred to as BVD is caused by infection with any one of three different species of virus: bovine viral diarrhea virus type 1 (BVDV1), bovine viral diarrhea virus type 2 (BVDV2) and a newly emerging group of viruses called HoBi-like viruses. So far the only BVD pathogens found in the United States are BVDV1 and BVDV2. All BVD pathogens may exist as one of two biotypes — cytopathic and noncytopathic. This designation has nothing to do with virulence but reflects whether or not viral infection of cultured epithelial cells results in cell death. In nature, viruses from the noncytopathic biotype predominate by a large margin and all high-virulence viruses are noncytopathic. In general, cytopathic viruses are only isolated from mucosal disease cases and are thought to arise from noncytopathic viruses via genetic recombination. There is a wide range of virulence among the noncytopathic viruses circulating in the field. However, most highly virulent viruses are rare. While it appears both biotypes may cross the placenta and infect the fetus, only viruses from the noncytopathic biotype establish persistent infection in the fetus. Because the immune system of the persistently infected fetus does not recognize viral proteins as foreign, the virus is never cleared, thus setting up a lifelong infection. While persistently infected animals (PIs) are the major vector for introducing BVD into herds and PIs tend to have more health problems than normal animals, most of the economic damage resulting from BVD is associated with acute infections.