Submitted to: American Association of Veterinary Laboratory Diagnosticians
Publication Type: Abstract only
Publication Acceptance Date: 7/15/2007
Publication Date: 10/18/2007
Citation: Fulton, R.W., Johnson, B.J., Hessman, B.E., Ridpath, J.F., Kapil, S., Burge, L.J., Braziel, B., Kautz, K., Reck, A. 2007. Utilization of multiple diagnostic tests to identify cattle with bovine viral diarrhea virus infections and persistence of positive tests in persistently infected cattle [abstract]. American Association of Veterinary Laboratory Diagnosticians 50th Annual Conference. p. 64. Interpretive Summary:
Technical Abstract: Bovine viral diarrhea virus (BVDV) infections have a significant impact on the cattle population and production. Persistently infected (PI) cattle represent the principal reservoir of infection. Identification and removal of PI animals are critical to the control of BVDV. There are numerous assays for BVDV including viral isolation, antigen capture ELISA (ACE), immunohistochemistry (IHC), and various polymerase chain reaction (PCR) assays. The objectives of this study included using different methods to identify PI cattle, and the duration and consistency of the positive results in PI cattle. These assays included viral isolation, ACE, IHC, and PCR using samples collected from 12 PI cattle held from day 0 to day 342 at approximately one month intervals. The PI cattle were penned together allowing commingling of the calves which were infected with BVDV1a, BVDV1b, or BVDV2a (four calves per subtype).The calves had received BVDV vaccine two to six months prior to the study. None of the viruses from the PI calves isolated were subtyped as of vaccine origin. Serums collected throughout the study were assayed for viral antibodies to these three BVDV subtypes. Cell culture assays for BVDV used two methods (1) qualitative cell culture assay (QCCA) based on positive antigen in bovine monolayer MDBK cultures; and (2) quantitative assay using viral titration (VT) in 96-well plates using staining for BVDV in MDBK cells. Viral isolation and titrations were performed on serums and nasal swab materials. The ACE test was used on serums, nasal swabs, and ear notches, and IHC was performed on notches. The reverse transcriptase (RT)-PCR was performed on serums, ear notches, and nasal swab materials. The detection limit based on dilution factors for the VT were: 10**1.6 per ml for serum and 10**2.9 per ml for nasal swabs. Nasal swab materials were obtained by placing commercial viral culturettes into 2 ml cell culture media. During the study 3 calves died with lesions of Mucosal disease. The cattle remained IHC and ACE positive in all ear notch collections from day 0 to day 342. The cattle were positive for virus in the nasal swabs by viral isolation for all collections with titers ranging from 10**3.4 to 10**7.85. There were instances the nasal swab materials were toxic to VT cultures. All the calves had virus in the serum with range of 10**1.6 to 10**5.35. One calf did not have quantifiable virus (<10**1.6) in the serum on three collections. All the PI calves were ACE positive on serums and the nasal swabs in collections throughout the study. PCR results were positive on serums, nasal swabs, and notches; however there were instances where calves were initially test negative by PCR, but positive on subsequent testing. Serotesting of the PI calves using day 0 and day 342 samples indicated that some, but not all of the PI calves seroconverted to heterologous subtypes (likely from the other PI calves). In summary, the PI cattle remained IHC and ACE positive on ear notch samples for the duration of the study (342) days without going negative at any time. The infectivity of the serum and nasal swabs indicates that the PI cattle remain as continual shedders of the virus throughout their life. The ACE and PCR tests on serums and nasal swabs may be used as screening tests, however repeated testing or confirmation with other tests are required to confirm PI status. Plus PI calves may respond to BVDV vaccinations or exposure to heterologous strains.