Severe Acute Bovine Viral Diarrhea in Ontario, 1993–1995

Abstract

Abstract. In 1993, noncytopathic bovine viral diarrhea virus (BVDV) strains with enhanced virulence caused unprecedented outbreaks of severe acute bovine viral diarrhea (BVD) in dairy, beef, and veal herds in Ontario (Canada). Fever, pneumonia, diarrhea, and sudden death occurred in all age groups of cattle. Abortions often occurred in pregnant animals. Gross lesions in the alimentary tract were similar to those associated with mucosal disease, especially in animals Ͼ6 months of age. Cattle of all age groups had microscopic lesions in the alimentary tract similar to those seen with mucosal disease. The epidemic peaked in the summer of 1993, with 15% of all bovine accessions from diseased cattle presented to the diagnostic laboratory being associated with BVDV. The virus strains involved in the outbreak were analyzed using monoclonal and polyclonal antibodies and the polymerase chain reaction. The virus isolates from these outbreaks of severe disease were determined to be type 2 BVDV. Type 2 BVDV has been present in Ontario at least since 1981 without causing widespread outbreaks of severe acute BVD, which suggests that type 2 designation in itself does not imply enhanced virulence. Cattle properly vaccinated with type 1 BVDV vaccines appear to be protected from clinical disease.

Clinical response and immunomodulation following experimental challenge of calves with type 2 noncytopathogenic bovine viral diarrhea virus

“…All calves tested BVDV-negative and BVDV-specific-antibody-negative [7] prior to inclusion in the study. The calves also tested negative for antibodies specific to bovine leukemia virus (BoviLeucotest, Diagnostics Biovet, St-Hyacinthe, Québec, Canada) and bovine immunodeficiency-like virus [2].…”

“…This virus was isolated during the BVDV outbreak in Ontario in the summer of 1993 from an aborted fetus from a herd that experienced acute gastrointestinal and respiratory disease, and death of calves and cows [7]. This virus has been propagated and titrated in cultures of bovine embryonic spleen cells as previously described [7].…”

“…Blood samples were collected from each calf on day 0 (just before virus exposure), and at days 3 to 12 postexposure (PE) for complete and differential white blood cell and platelet count determination upon standard procedures [14], BVDV isolation from buffy coat white blood cells on bovine embryonic spleen cells [7], and isolation of peripheral blood mononuclear cells (PBMCs) in RPMI 1640 medium by using Ficoll-diatrizoate gradient centrifugation [4] for cell immunophenotyping and phagocytosis analyses. A microtiter virus neutralizing assay [7] was performed to determine the presence of serum BVDV-specific neutralizing antibodies at day 12 PE, using known positive and negative control sera, 100 TCID 50 of a type 2 cp BVDV isolate (NVSL125c) as the challenge dose and MDBK cells.…”

“…More recently, severe acute outbreaks of BVDV-associated disease in young and adult cattle have been documented in Northeastern United States [21] and in the provinces of Québec [13,22] and Ontario [7] in Canada. In general, the disease was characterized by thrombocytopenia, leukopenia, fever, hemorrhages, diarrhea and death, and was attributed to ncp BVDV isolates.…”

“…In general, the disease was characterized by thrombocytopenia, leukopenia, fever, hemorrhages, diarrhea and death, and was attributed to ncp BVDV isolates. These isolates, on the basis of sequence comparison in the 5' untranslated region of the viral genome and antigenic analysis with panels of monoclonal antibodies, were determined to be BVDVs type 2 isolates [7,22,26], as opposed to the BVDV type 1 isolates.…”