|Carman, S - ONTARIO MINISTRY OF AGR|
|Van Dreumel, T - ONTARIO MINISTRY OF AGR|
|Hazlett, M - ONTARIO MINISTRY OF AGR|
|Alves, D - ONTARIO MINISTRY OF AGR|
|Dubovi, E - CORNELL UNIVERSITY|
|Tremblay, R - ONTARIO MINISTRY OF AGR|
|Godkin, A - ONTARIO MINISTRY OF AGR|
|Anderson, N - ONTARIO MINISTRY OF AGR|
Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 1997
Publication Date: N/A
Interpretive Summary: Bovine viral diarrhea virus is a common viral pathogen of cattle. Usually, this virus induces inapparent to mild disease characterized by low grade fever, inappetence, decreased milk production in dairy cattle, and abortion in pregnant cattle. Between 1993 and 1995, unusually virulent strains of bovine viral diarrhea virus induced disease of epidemic proportions in the Ontario province of Canada. High fever, pneumonia, and diarrhea were observed in afflicted cattle. In some herds, death loss exceeded 10% of cattle over one year of age and 50% of cattle under one year of age. The viruses isolated from several Ontario farms were characterized and found to belong to the recently identified type 2 group of bovine viral diarrhea virus. The epidemic was caused by the emergence of unusually virulent bovine viral diarrhea viruses which spread through cattle herds that were not vaccinated for bovine viral diarrhea. Vaccinated herds were protected from severe disease. The report of this epidemic provides information on clinical signs of disease and economic loss associated with virulent bovine viral diarrhea viruses. Also, this epidemic clearly points out the need for producers to vaccinate for bovine viral diarrhea virus.
Technical Abstract: The information gathered during this outbreak of severe BVD in Ontario shows that acute BVDV can result in major economic losses to the cattle industry, with death of animals of all ages due to pneumonia, diarrhea, abortions, and death after only brief periods of illness. Alimentary lesions in animals can be as severe and similar to those described for mucosal disease. Gross lesions in acute BVD cases vary distribution and extent, and may be minimal in animals less than 6 months of age. The most consistent microscopic lesions are evident in the small intestine, including the Peyer's patches in all age groups. The outbreak was attributed to Type 2 BVDV using cross-neutralization assays and PCR typing technology. Disease attributed to Type 2 BVDV was readily diagnosed using standard reagents for BVDV Type 1. Both Type 1 and Type 2 BVDV have been present in Ontario since at least 1981, yet severe disease has only been recognized in the provincial herd since 1993. This indicates that BVDV Type 2 designation does not, in itself, imply enhanced viral virulence. During this outbreak, only cattle not properly vaccinated according to manufacturer's instructions using Type 1 BVDV vaccines succumbed to severe disease, suggesting that Type 1 vaccines can provide protection for Type 2 BVDV. However, the antigenic segregation seen between Type 1 and Type 2 BVDV in virus cross-neutralizing tests done with polyclonal antibody dictates the need for studies to determine the significance of these antigenic variations, as they pertain to the clinical expressions of BVDV infection.