|Cox, Elizabeth - Merck Animal Health|
Submitted to: Bovine Practitioner Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2017
Publication Date: 9/1/2017
Citation: Cox, E.A., Ridpath, J.F., Falkenberg, S.M. 2017. Clinical report: Detection and management of bovine viral diarrhea virus Type 1b in a large dairy herd. Bovine Practitioner Journal. 51(2):153-156.
Interpretive Summary: Vaccination against bovine viral diarrhea virus (BVDV) is a common practice as a preventative measure to protect against fetal exposure to BVDV and subsequently fetal infection. Fetal infection with BVDV between 40-125 days of gestation, can induce a state of viral tolerance in the fetus that leads to lifelong viral persistence and ultimately produces persistently infected (PI) calves. In most recent epidemiological studies BVDV type 1b PI calves were most prevalent. Commercially available modified-live BVDV vaccines only contain BVDV type 1a and 2a. Research has suggested that while BVDV vaccination is a method of prevention in acute infections, the level of protection needed to prevent fetal infection is much greater. Data from this field study demonstrates the lack of protection that can be observed in a field situation using currently available modified-live vaccines. Lack of observable clinical signs associated with BVDV is not a reliable measure of BVDV control and BVDV testing programs should be implemented to control BVDV infections.
Technical Abstract: Case Description: 1,081 newborn calves from a commercial dairy were tested for bovine viral diarrhea virus antigen by pooled RT-PCR as part of a screening program. Ear tissue from twenty six calves initially tested positive and 14 confirmed positive with antigen capture ELISA two weeks later (1.3%). Immunohistochemistry conducted on a third sample collected from 13 of the 14 confirmed persistent infections. When these calves were born, the dairy was using a modified live BVD vaccine and clinical BVDV infections had not been recognized. The BVD was typed in the PI calves to better understand the epidemiology of the PI’s calves detected. Clinical Findings: Ten of the calves were available for BVD typing. Both cytopathic (cpe) and non-cytopathic (non-cpe) BVD viruses were isolated. The non-cpe viruses typed as BVD type 1b with a total of 3 different strains found; an identical strain found in two calves, another identical strain found in two other calves and a third identical strain found in three other calves. Treatment and Outcome: BVDV PI calves were removed and a BVD control program was implemented that included BVDV testing and a reevaluation of the vaccination protocol. Clinical Relevance: A BVD vaccination program using a modified live vaccine did not protect this herd from the formation of BVD type 1b PI calves. These results demonstrate that control programs that rely only on observation of clinical disease and vaccination to control BVDV without testing for the presence of PI animals are not adequate to control BVD.