The profile of bovine viral diarrhea virus (BVDV) infection was studies in a high production dairy herd selected based on a history of reproductive failures and regular vaccination against BVDV. Virus identification was performed by RT-PCR and serological profile was determined by virus-neutralization (VN). Initially, 100% (n=692) of the animals in the herd were monitored for identification of an active infection by RT-PCR in sera. Four months later, all positive animals (n=29) were retested by RT-PCR, along with newly born animals (n=72), or those that had reproductive failures (n=36) in the interval. The RT-PCR assay identified 27 transiently infected animals and three persistently infected (PI). Serology performed only in positive animals in the first RT-PCR and in cows with reproductive failures between the first and second RT-PCR analysis, showed large variation VN antibody titers and seroconversion in most animals. Increases in VN titers were demonstrated, with variation between 3 and 8 log2, indicating virus circulation within the herd. Virus circulation in the vaccinated herd evaluated in this study was likely responsible for reproductive failures observed in cows with low VN titers and for fetal infections. These results demonstrate that control of BVDV infection by regular vaccination in dairy cattle herds with PI animals represents a great challenge for the prophylaxis of this infection.
Diagnosis; bovine viral diarrhea virus; BVDV; persistent infection; RT-PCR; virus-neutralization; vaccine
