Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 29, 1999
Publication Date: N/A
Interpretive Summary: The term bovine viral diarrhea virus (BVDV) does not refer to a single virus but to a group of viruses. These viruses are grouped together because they have many similarities. While they may be alike in many ways, they have some important differences that we need to understand before we can do a good job of recognizing and controlling BVDV infections through vaccination. Recently, it has been shown that BVDV are actually made up of two groups of viruses. These two groups are called BVDV1 and BVDV2. Much of the research that has been done to date has been done using BVDV1 viruses, so not a lot is known about the BVDV2 viruses. In this study we have looked at BVDV2 viruses. We found that they cause diseases that range from very mild to very severe depending on which BVDV2 virus is used. Understanding that not all BVDV2 behave the same way will help veterinarians' diagnosis of BVDV infections. These studies will be of great benefit to the dairy industry worldwide.
Technical Abstract: Detection and control of bovine viral diarrhea virus (BVDV) is hampered by viral heterogeneity that results in differences in neutralizing epitopes, cytopathology and virulence. Recently it was found that there are 2 different genotypes, BVDV1 and BVDV2, among BVDV. BVDV2 isolates make up a significant proportion of the BVDV isolated in North America. BVDV2 viruses can be distinguished from BVDV1 and other pestiviruses by serology and Mab binding. Like the BVDV1 viruses, BVDV2 viruses may exist as one of 2 biotypes, cytopathic or noncytopathic, based on their activity in cultured cells. Cytopathogenic effects on cultured cells does not correlate with virulence in vivo. BVDV2 isolates may differ from BVDV1 isolates in the processing of the E2 glycoprotein. Variation among BVDV1 and BVDV2 in the 5' UTR are similar. Phylogenetic analysis and differences in virulence suggest that BVDV2 are heterogeneous. Symptoms resulting from BVDV2 infections may range from clinically inapparent to clinically severe. Recently, disease outbreaks associated with acutre uncomplicated BVDV infection have been reported in the U.S. and Canada. These outbreaks of clinically severe disease, termed hemorrhagic syndrome (HS), were all associated with viruses from the BVDV2 genotype. Not all BVDV2 isolates cause clinically severe disease. Avirulent BVDV2 isolates do exist and may predominate over virulent BVDV2 in nature. When virulent BVDV2 viruses are inoculated into calves they induce a disease characterized by fever, diarrhea, leukopenia, lymphopenia, neutropenia, thrombocytopenia, and death. Infection with avirulent BVDV2 results in a reduction of leukocytes that may be accompanied by a low grade fever. These viruses do not cause cliical disease or a cliical leukopenia.