Submitted to: American Association of Veterinary Laboratory Diagnosticians
Publication Type: Abstract Only
Publication Acceptance Date: July 15, 2007
Publication Date: October 18, 2007
Citation: Ridpath, J.F., Neill, J.D., Peterhans, E. 2007. Improved BVDV-1b challenge model for evaluating efficacy of protection against clinical signs following acute infection [abstract]. American Association of Veterinary Laboratory Diagnosticians 50th Annual Conference. p. 63. Technical Abstract: Introduction: Efficacy of bovine viral diarrhea virus (BVDV) vaccines in preventing acute infections is evaluated based on reduction of clinical disease. While high virulence BVDV2 strains are used in U.S. vaccine efficacy studies, the BVDV1 strain, NY-1, made available by the USDA as a challenge strain, produces very little in the way of clinical disease. Further, NY-1 is also present in at least one commercial vaccine. In order to identify a BVDV1 strain that generates a more pronounced clinical presentation, clinical presentation following inoculation with three field strains were compared to clinical presentation following inoculation with NY-1. Materials and Methods: The strain NY-1 was isolated, by researchers at Cornell University, from dairy cattle residing in the United States. Strains 5013 and 2360 were isolated at the University of Bern Institute of Veterinary Virology from animals suffering from bloody diarrhea and pyrexia. Strain CA0401186a was isolated from tissues from a PI calf submitted to the National Animal Disease Center (NADC) by diagnosticians from the Tulare Laboratory of the California Animal Health and Food Safety Laboratory. All viruses were characterized as noncytopathic based on growth characteristics in MDBK cells. Based on phylogenetic analysis, strains NY-1 and CA0401186a were segregated to the BVDV1b subgenotype, strain R5013 to the BVDV1k subgenotype and R2360 to the BVDV1e subgenotype. Three-to-nine-month-old Holstein calves were tested free of BVDV virus in buffy coat (BC) samples by virus isolation, free of BVDV antibodies in serum and free of BVDV antigen in ear notch samples by immunohistochemistry. Animals were inoculated via the nasal route with 5 ml of the appropriate viral dose in cell culture medium. Inoculated animals were individually penned in a climate-controlled barn for the duration of the experiment and observed a minimum of twice daily for cough or loose stool. Basal temperatures were taken daily from day -2 to day 14 post inoculation. Blood samples for virus isolation, determination of circulating lymphocytes and platelet counts and determination of presence of serum neutralizing antibodies were collected on days -2, 3, 6, 9, 11 and 13 post inoculation. These time points correlated with the typical first observation of clinical signs (day 3), midpoint of clinical disease (days 6 and 9), and recovery (day 13) based on previous studies. Results: All virus inoculated animals inoculated developed serum titers greater than 1:4 by day 13. Virus was isolated from the buffy coat of all animals virus inoculated at least once between days 3 and 11 post inoculation. There were not significant differences between number of days virus was isolated or serum titers between inoculated groups. Neither serum antibodies nor virus were detected in any of the control animals. Infection with any of three of the BVDV1 field strains resulted in a clinical presentation that was more severe than that observed with NY-1. The decrease in lymphocytes and the development of loose stools was significantly greater following infection with R5013 compared to NY-1. The number of animals developing temperatures greater than 41.1'C (106'F) was greater following infection with either BVD 2360 or CA0401186A. Further there was a significantly greater decrease in circulating platelets following infection with CA0401186A. Conclusions: Based on these results, strain CA0401186A was selected as a potential challenge strain. The clinical presentation following inoculation with this virus was reproducible and was not dependent on dose over two logs of virus.