Efficacy of a combination viral vaccine for protection of cattle against experimental infection with field isolates of bovine herpesvirus-1.

Abstract

OBJECTIVE: To determine whether a combination viral vaccine containing a modified-live bovine herpesvirus-1 (BHV-1) would protect calves from infection with virulent field strains of BHV-1 for weeks or months after vaccination. DESIGN: Randomized controlled trial, performed in 2 replicates. ANIMALS: 63 weaned 4- to 6-month-old crossbred beef calves seronegative for antibody against BHV-1. PROCEDURES: Calves were randomly allocated to 1 of 2 treatment groups. Control calves (n = 10/replicate) received a combination modified-live mixed viral vaccine without BHV-1, and treatment calves (20 and 23/replicate) received a combination modified-live mixed viral vaccine containing BHV-1. Each group was challenged via aerosol with 1 of 2 field strains of BHV-1, 30 days after vaccination in replicate 1 and 97 days after vaccination in replicate 2. After challenge, calves were commingled in 1 drylot pen. Clinical signs, immune responses, and nasal shedding of virus were monitored for 10 days after challenge, after which the calves were euthanatized and tracheal lesions were assessed. RESULTS: Vaccination stimulated production of BHV-1-specific IgG antibody that cross-neutralized several field and laboratory strains of BHV-1. Challenge with both field strains of BHV-1 resulted in moderate to severe respiratory tract disease in control calves. Treatment calves had significantly fewer signs of clinical disease, shed less BHV-1, had less or no weight loss after challenge, and had fewer tracheal lesions than control calves for at least 97 days after vaccination. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of the combination modified-live BHV-1 vaccine yielded significant disease-sparing effects in calves experimentally infected with virulent field strains of BHV-1.