COUNTERMEASURES TO CONTROL AND SUPPORT ERADICATION OF BOVINE VIRAL DIARRHEA VIRUS (BVDV)
Location: Ruminant Diseases and Immunology Research Unit
Title: BVDV infection of pregnant white-tailed deer (Odocoileus virginianus)
Submitted to: European Society for Veterinary Virology
Publication Type: Abstract Only
Publication Acceptance Date: June 16, 2008
Publication Date: September 16, 2008
Citation: Ridpath, J.F., Duncan, C., Chase, C.C., Driskell, E., Palmer, M.V., Spraker, T., Neill, J.D. 2008. BVDV Infection of Pregnant White-Tailed Deer (Odocoileus virginianus) [abstract]. 7th International Pestivirus Symposium, European Society of Veterinary Virology. p. 64.
Aim: Serological, experimental and individual case studies have explored the presence and pathogenesis of the virus in wild ungulates; however there remain large gaps in knowledge regarding BVDV infection in non-bovine species. Previously we have shown that inoculation of white-tailed deer (Odocoileus virginianus) with bovine viral diarrhea viruses (BVDV) results in acute infection accompanied by pyrexia and lymphoid depletion. Two questions, important to eradication efforts, are whether persistently infected white-tailed deer can be generated following infection of pregnant does and if so can they be detected using currently available tests. The purpose of this study was to determine the outcome of BVDV infection in pregnant white-tailed deer.
Methods: The two viruses, R03-24272 (genotyped as BVDV1) and R03-20663 (genotyped as BVDV2), used in this study were isolated from two different deer carcasses submitted to South Dakota State University for diagnostic testing. Ten white-tailed deer were purchased from a commercial breeder and housed in BSL2 containment for the duration of the experiment. Does were determined to be BVDV negative by virus isolation from buffy coat. Pregnancy status was confirmed using an enzyme-linked immunosorbent assay (ELISA) test that measures the presence of pregnancy-specific protein B (PSPB) in serum. The stage of pregnancy was calculated based on date of contact with buck. Does were estimated to be between 4 to 5 weeks pregnant at the time of purchase. After purchase does were allowed to acclimate to housing for 10 days prior to viral inoculation. Thus, at inoculation, does were estimated to be between 6 and 7 weeks pregnant. Does were observed until 182 days post inoculation. As the gestation length for white-tailed deer averages between 193 – 205 days, the observation period for this experiment (182 days post inoculation) extended at least 3 weeks past the normal gestation length for this species.
Does were inoculated, by the nasal route, with 5 mls of 1.0 x 106 tissue culture infectious dose (TCID)/ml of either R03-24272 or R03-20663. The original design of the study was to inoculate seven deer with the strain RO3-020633. Clinically mild disease was observed in a preliminary study in which white tailed fawns were infected with this isolate. However, the death of two of the inoculated does within the first two weeks following inoculation, raised fears that this virus could be more virulent in adults than originally assumed. For this reason an additional 3 does were added to the study. These does were inoculated with the virus RO3-24272. Does were housed 2 to a pen in a climate-controlled barn, operated at a BSL2 containment level, for the duration of the experiment and observed a minimum of twice daily for attitude, cough, loose stool or abortion. Fetal age of aborted/dead fetuses was estimated based on crown to rump length.
Levels of BVDV neutralizing serum antibodies were determined prior to inoculation and 21 or 35 days post inoculation. Two of the does had serum antibody titers against BVDV (>512) prior to inoculation, the remaining 8 does were seronegative.
Results: Both seropositive animals gave birth to normal fawns. Of the remaining 8 seronegative animals four died (death between 8 to 79 days post inoculation), one apparently readsorbed its fetus, two aborted and one gave birth to two probable PI fawns. BVDV was isolated from fetuses, maternal tissues and PI fawns. Ear notches of PI fawns were positive by ACE. The twin PI fawns died at one day of age from trauma unrelated to the infection and tissues were collected for histological and immunohistochemical examination. The only histological abnormality was diffuse depletion of B-lymphocytes in both fawns. BVDV antigen was distributed widely throughout many tissues and cell types, most notably epithelium and vascular endothelium, consistent with that reported in cattle. In contrast to cattle, lymphocytes exhibited only very rare positive staining.
Conclusions: The clinical relevance of this study is that BVDV associated reproductive disease in white-tailed deer and cattle is similar. However, persistently infected (PI) fawns differed from PI cattle in the amount of virus associated with lymphocytes. This suggests that there may be differences in the replication and shedding of the virus between cattle and cervids. Diagnostic methods developed for cattle, including virus isolation and detection of BVDV antigen or genomic material performed adequately in white tail deer. Finally, the presence of neutralizing antibody titers in pregnant white-tailed deer appears to protect against BVDV infection in fawns.