Immunisation of pigs against experimental infection with Bordetella bronchiseptica.

During pregnancy seven minimum-disease sows (group A) were infected intranasally with Bordetella bronchiseptica, fed with the killed bacterium periodically and inoculated parenterally with a dead vaccine eight, six and two weeks before parturition. Groups B and C, isolated from A until farrowing, contained respectively six sows given the vaccine parenterally and eight control sows. At parturition, group A had much higher average agglutinin titres in the serum and colostrum than B or C. Group A sows gave their piglets a better passive protection against infection with B bronchiseptica strain 293 and its effects in the respiratory tract during the first eight weeks of life, especially in those exposed to spontaneous infection with bordetellae from a littermate deliberately inoculated intranasally 24 hours after birth. Passive antibody strongly affected the capacity of piglets to respond actively to parenteral vaccination (when seven and 28 days old), marked humoral responses being noted only in those from group C sows. Vaccination of piglets exposed to infection by contact reduced neither the prevalence or intensity of the nasal infection, the amount of turbinate atrophy or pneumonia nor significantly improved weight gain compared with unvaccinated littermates. Unlike their eight-week-old littermates there was little hypoplasia and no pneumonia in infected pigs (whether vaccinated or not) when they reached five months of age.