bInfection of cattle with Neospora caninum may result in abortion or the birth of a congenitally infected calf. Vaccination with live N. caninum protects against experimental infection of cattle and mice, and the naturally attenuated Nc-Nowra strain of N. caninum is of particular interest as a potential vaccine candidate. Vaccination of heifers prior to breeding with live Nc-Nowra tachyzoites by either the subcutaneous or the intravenous route reduced the rate of abortion and the presence of the parasite in calves as determined by PCR and serology after infection of cows with a virulent isolate. Protected fractions were 55.6% to 85.2% depending on the route of vaccination and growth conditions of the vaccine strain, with cryopreserved Nc-Nowra tachyzoites being less effective, with a 25.9% protected fraction. Vaccination appeared to reduce the rate of pregnancy after artificial insemination in some groups compared to nonvaccinated, nonchallenged controls. One animal that was vaccinated but not challenged experienced an abortion, but Nc-Nowra could not be detected in any of the cows in this group or their progeny. This study confirms that live vaccination can be an effective method of preventing neosporosis in cattle and yet highlights the technical hurdle of preservation of live parasites that must be overcome for a vaccine to be commercially successful.

Administration of a multivalent MLV vaccine containing M haemolytica toxoid protected calves against challenge exposure with virulent B trehalosi by reducing the mortality rate, lung lesion scores, and clinical scores for respiratory disease.

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.

Efficacy of attenuated (att) bovine respiratory syncytial virus (attBRSV) as an antigen fraction in a multivalent 6-way vaccine containing modified-live virus and an inactivated Mannheimia haemolytica bacterin-toxoid was given as a single subcutaneous injection, and evaluated by an aerosol challenge by nebulization in young calves with virulent BRSV strain 21 d after vaccination. A total of 32 Holstein calves, seronegative to BRSV and 60 days-of-age at the time of vaccination, were used in the study. Calves were allocated to 2 treatment groups with 16 animals per group, and received either a single dose of a modified-live bovine herpes virus-1, bovine viral diarrhea virus, parainfluenza 3 virus, bovine respiratory syncytial virus vaccine + M. haemolytica bacterin-toxoid, or corresponding placebo formulation without targeted BRSV antigen. Administration of the 6-way vaccine containing BRSV fraction induced significantly higher virus-neutralizing antibody (p=0.0003) and anti-BRSV IgG titers (p=0.0006) in vaccinated animals compared to the placebo group. Consequently, BRSV-vaccinated calves had significantly (p<0.0001) higher arterial partial pressures of oxygen (PaO2), significantly (p<0.0001) lower percentage of lung lesions, and significantly reduced mortality rate (p<0.0001) than did placebo vaccinated calves subsequent to BRSV challenge. Furthermore, there was a 61.2% reduction in virus shedding and duration of shedding (p<0.0001), indicating strong vaccine efficacy.

Efficacy of attenuated (att) bovine viral diarrhea virus (types 1 and 2) as antigen fractions in a modified-live multivalent vaccine were evaluated following single, subcutaneous (SC) administration and intranasal (IN) challenge 35 to 38 d after vaccination, with either virulent BVDV-1b (Study 1) or BVDV-2 (Study 2) viruses in young calves. A total of 80 BVDV-seronegative Holstein calves, 53 to 61 d of age at the time of vaccination, were used in 2 separate studies with 40 animals per study. In each study, calves were allocated to 1 of 2 treatment groups (20 animals per group) which received either a single dose of combination modified-live bovine rhinotracheitis (BHV-1)-bovine virus diarrhea-parainfluenza 3-respiratory syncytial virus vaccine + Mannheimia haemolytica toxoid, or corresponding placebo formulation without targeted test antigen fractions attBVDV-1a and attBVDV-2. In the respective studies, multivalent vaccine induced significantly higher virus neutralizing antibody responses and reduced incidence and duration of leukopenia and viremia in vaccinated animals compared to placebo-treated animals. Post-challenge leukopenia, a hallmark of BVDV infection, was observed in 75% and 100% of control calves compared to only 26.3% and 25% in vaccinated animals in Study 1 and Study 2, respectively (p=0.006; p=0.0001). In addition, duration of leukopenia was significantly shorter in vaccinates compared to placebo controls (p=0.0091 Study 1; p<0.0001 Study 2). Furthermore, 100% of placebo-treated calves in both studies were viremic compared to 57.9% (Study 1) and 25% (Study 2) of vaccinated animals, resulting in significant reduction of post-challenge viremia (p=0.0012, Study 1; p=0.0001, Study 2). The duration of viremia was significantly shorter (p<0.0001) in vaccinated groups compared to control calves in both studies. In conclusion, data from the current studies demonstrated vaccine efficacy in 60-day-old calves against BVDV-1b and BVDV-2 infection.