Objective—To determine whether a combination modified-live bovine respiratory syncytial virus (BRSV) vaccine could stimulate protective immunity in young BRSV-seropositive calves following intranasal administration and determine the duration of clinical immunity.
Design—Controlled challenge study.
Animals—84 dairy calves (3 to 11 days old).
Procedures—Responses to BRSV challenge of seronegative calves vaccinated under licensing trial conditions were compared with those of seropositive calves 2 times after vaccination. In experiment 1, young BRSV-seronegative calves were vaccinated intranasally with a minimum immunizing dose of BRSV and challenged with BRSV approximately 7 weeks later. In experiments 2 and 3, young BRSV-seropositive calves were vaccinated intranasally with a commercially available combination modified-live virus vaccine containing the commercial dose of the BRSV fraction and challenged with BRSV 9 weeks or approximately 14 weeks later, respectively.
Results—In experiments 1 and 2, BRSV-vaccinated calves had significantly higher Pao2, significantly fewer lung lesions, and significantly lower mortality rate than did unvaccinated calves subsequent to BRSV challenge. In contrast, in experiment 3, there were no differences in Pao2, lung lesions, or mortality rate between vaccinated and control calves after BRSV challenge approximately 14 weeks after vaccination. Protected calves in experiment 1 consistently had significant anamnestic mucosal and systemic antibody responses after challenge, whereas in experiments 2 and 3, antibody responses after challenge were more variable.
Conclusions and Clinical Relevance—A combination BRSV vaccine administered intranasally to young calves induced protective immunity in the presence of maternal antibodies. The duration of immune responses induced by intranasal vaccination was short (≤ 4 months). Boosting immunity iatrogenically, or by natural exposure, is probably required to obtain optimal responses to neonatal intranasal vaccination.
OBJECTIVE To evaluate efficacy and duration of immunity of the bovine herpesvirus type 1 (BHV-1) fraction of a trivalent vaccine also containing parainfluenza virus-3 and bovine respiratory syncytial virus fractions administered intranasally (IN) for protection of calves against infectious bovine rhinotracheitis (IBR).
DESIGN Controlled challenge study.
ANIMALS 120 dairy calves (3 to 8 days old) seronegative for antibody against BHV-1 (experiments 1 and 2) or seropositive for maternally derived antibody against BHV-1 (experiment 3).
PROCEDURES In 3 separate experiments, calves were vaccinated IN via 2 nostrils (experiment 1) or 1 nostril (experiments 2 and 3) with a vaccine containing or not containing a BHV-1 fraction. For seronegative calves, the test vaccine contained a minimum immunizing dose of BHV-1; for seropositive calves, it contained a commercial dose of BHV-1. Calves were challenged IN with virulent BHV-1 on day 28 or 193 (seronegative calves) or day 105 (seropositive calves) after vaccination to evaluate vaccine efficacy. Frequency and duration of clinical signs, rectal temperatures, virus shedding, and serologic responses were compared between treatment groups within experiments.
RESULTS In all experiments, BHV-1 vaccinated calves had lower frequencies or shorter durations of clinical signs of IBR than did control calves. Following viral challenge, peak rectal temperatures and degrees of virus shedding were lower and serologic responses were higher in vaccinated versus control calves.
CONCLUSIONS AND CLINICAL RELEVANCE IN vaccination against BHV-1 protected all calves against clinical IBR disease, regardless of serologic status at the time of vaccination, and suppressed virus shedding. A single dose of this IN vaccine has the potential to protect seronegative calves for at least 193 days and override maternally derived antibody to protect seropositive calves for at least 105 days.