Anotace:
This study demonstrated the duration of immunity over 6 months of a vaccine against key bovine respiratory disease pathogens: Parainfluenza 3, Bovine Respiratory Syncytial Virus, Bovine Viral Diarrhoea and Mannheimia haemolytica. This was performed by challenge on colostrum-deprived calves at the age of 2 weeks. Recent European field isolates were used as challenge strains. Clinical signs and pathogen excretion or presence were monitored. Field relevance of the viral challenge strains was analysed using phylogenic analysis. Significant reduction of excretion of the 3 viruses in vaccinated animals was a consistent finding, demonstrating the efficacy of the vaccine. Reducing shedding is indeed key to interrupting the infection transmission chain and helping to achieve the protective effects of immunisation that extend beyond the individual. A significant reduction of clinical signs and lung lesions following the Mannheimia haemolytica challenge was also observed in vaccinated animals versus controls. Comparison of the challenge strains to an array of global and European strains, including recent ones, demonstrated a high genetic proximity, supporting the potential for the vaccine to maintain similar levels of efficacy in the field over a 6-month period post vaccination.