Differences in virulence between two noncytopathic bovine viral diarrhea viruses in calves.
A noncytopathic bovine viral diarrhea virus (BVDV), BVDV-890, isolated from a yearling heifer that died with extensive internal hemorrhages, was compared for virulence in calves with noncytopathic BVDV-TGAN, isolated from an apparently healthy persistently infected calf. After challenge exposure with BVDV-890, nonimmune calves (n = 7) developed fever > 40 C, diarrhea, leukopenia, lymphopenia, neutropenia, and thrombocytopenia. Most calves (n = 6) died or were euthanatized by 19 days after challenge exposure. Challenge exposure with BVDV-890 did not induce disease in 2 calves that had congenital persistent infection with BVDV or in 3 calves that had neutralizing antibody titer > 4 against BVDV-890. After challenge exposure with BVDV-TGAN, nonimmune calves (n = 7) developed fever > 40 C and, rarely, diarrhea or lymphopenia. All of those calves survived challenge exposure. The average maximal titer of BVDV-890 isolated from serum was 1,000 times that of BVDV-TGAN. In calves infected with BVDV-890, the average maximal percentages of lymphocytes and platelets associated with virus were greater than those found in calves infected with BVDV-TGAN. Additional findings of epidemiologic significance were prolonged shedding of virus and delayed production of viral-neutralizing antibody in 1 calf challenge-exposed with BVDV-890. Also, after production of neutralizing antibody, mutant virus that was refractory to neutralization was isolated from calves challenge-exposed with BVDV-TGAN.
Bolin
S R
SR
Virology Cattle Research Unit, National Animal Disease Center, USDA, Ames, IA 50010.
Ridpath
J F
JF
D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D001912:Bovine Virus Diarrhea-Mucosal Disease / Q000382:microbiology* / Q000473:pathology; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology* / Q000473:pathology; D003588:Cytopathogenic Effect, Viral; D001908:Diarrhea Viruses, Bovine Viral / Q000276:immunology / Q000302:isolation & purification / Q000472:pathogenicity*; D009500:Neutralization Tests / Q000662:veterinary; D014774:Virulence
D000914:Antibodies, Viral