Evaluation of the Onset of Protective Immunity from Administration of a Modified-live, Non-adjuvanted Vaccine prior to Intranasal Challenge with Bovine Herpesvirus-1
Study objectives were to determine if subcutaneous administration of a modified-live, non-adjuvanted vaccine containing bovine herpesvirus-1 (BHV-1) at five, three, or two days pre-challenge, would reduce clinical signs, rectal temperatures, and viral shedding, and enhance serological response to BHV-1. Colostrumdeprived, neonatal calves (n = 48) were randomly assigned to six treatment groups, each containing eight calves. Treatment groups were based on administration of vaccine (VAC) or saline controls (CON) and day of administration (day -5, -3 or -2) relative to intranasal BHV-1 challenge (day 0). Following challenge, calves were monitored for clinical signs, rectal temperature, seroconversion, and quantity of BHV-1 recovered by virus isolation from nasal swabs. Data for the evaluation period (days 4-14) were analyzed using multivariable statistics. Day -5 and -3 VAC groups had fewer (P < 0.05) days of clinical illness compared to CON. Rectal temperatures were lower (P < 0.05) during days 4-8 for each of the VAC groups as compared to combined CON groups. CON calves shed BHV-1 for more days than calves vaccinated on day -5 (P < 0.01), day -3 (P = 0.06), or day -2 (P = 0.06). Mean concentrations of nasal BHV-1 also differed (P < 0.05) between combined CON groups and each of the VAC groups during at least one study day. Calves in the VAC groups (median = 10 days) seroconverted to BHV-1 (P < 0.01) sooner than CON calves (median = 14 days). This study demonstrated that the use of a non-adjuvanted MLV vaccine in neonatal calves can reduce the effects of BHV-1 challenge soon after vaccination.