A case report: evidence for type 2 bovine viral diarrhea virus (BVDV)-associated disease in beef herds vaccinated with a modified-live type 1 BVDV vaccine.

Abstract

Fetal infections with bovine viral diarrhea virus (BVDV) may result in infertility, abortions, stillbirths, developmental anomalies, and weak calves.1 Infection of the fetus from 58 to 120 days of gestation may create persistently infected (PI) calves that shed the virus continuously and perpetuate the herd infection.10,11 In beef herds, calf losses and PI calves have a significant impact on herd productivity.14 Vaccination with modified live virus (MLV) BVDV vaccines is commonly practiced in Wyoming beef herds to prevent reproductive losses due to BVDV infection. However, the majority of BVDV isolates obtained at the Wyoming State Veterinary Laboratory (WSVL) are from vaccinated herds. For example, in 1996 BVDV was isolated from 30 herds for which vaccination histories were available. Twenty-four herds had a history of BVDV vaccination and 6 were not vaccinated for BVDV. BVDV-associated diseases in beef herds vaccinated with inactivated BVDV vaccines have been reported.8,9 Here, we describe the isolation of type 2 BVDV-associated reproductive losses in beef herds where the cows were vaccinated with a type 1a MLV-BVDV vaccinea and the use of serology to detect BVDV infection retrospectively. In the fall of 1995, 28 cow–calf herds located in Weston County, Wyoming, had unusually high infertility rates followed by abortions, stillbirths, and weak calves in the spring of 1996. In 9 herds, the dams were vaccinated with the type 1a MLV-BVDV vaccine.a Gross findings in aborted fetuses and neonatal calves included hemorrhage in the subcutaneous tissues of lower extremities, muscle, and myocardium and on the serosal surfaces of multiple organs, serosanguinous fluid in thorax and abdominal cavities, and lens opacities. Fourteen animal tissue samples from 13 ranches were submitted. These animals included 5 fetuses, 6 neonatal calves, 2 calves 1 and 5 months of age, and a yearling steer. Two of the fetuses were autolyzed, and the remaining tissues were collected 15 minutes to 18 hours postmortem. Virus isolations (VI) were performed using 10% tissue homogenates in Bovarnick’s solution (0.218 M sucrose, 3 mM KH2PO4, 7.2 mM K2HPO4, 5.4 mM L-glutamic acid, 500 mg/liter streptomycin, 0.001% phenol red, pH 7.2) clarified by centrifugation and used to inoculate primary bovine embryonic testicle (BeT) cells previously tested and found negative for adventitial BVDV infection. Inoculated BeT cells were passed twice and stained for BVDV using monoclonal antibody 20.10.6b and fluorescein isothiocyanate-conjugated goat anti-mouse antibodyc as previously described.18 Blood samples from calves were collected from the jugular