Protective role of maternal antibodies against Haemophilus parasuis infection.

OBJECTIVE: To evaluate the impact of maternal antibodies after challenge exposure of baby pigs with a homologous serovar of Haemophilus parasuis. ANIMALS: 7 gilts and their litters from a high health status farm. PROCEDURE: Gilts were vaccinated twice with a commercial bacterin that contained H parasuis serovar 4 and 5 or, as a control, adjuvant only. A group of pigs was also vaccinated similarly before challenge exposure. After early and late challenge exposure at 3 and 4 weeks, respectively, all pigs from vaccinated gilts were evaluated for clinical signs of infection, lesions, and antibody titer. RESULTS: All pigs coming from control gilts had severe signs of H parasuis infection. Macroscopic lesions included polyserositis and pneumonia, and bacteriologic examination confirmed H parasuis as the etiologic agent. Vaccinated pigs born to vaccinated gilts did not have clinical signs of disease. However, some vaccinated pigs born to control gilts had signs of nervous system dysfunction and lameness. There was no difference in lesion scores between early or late challenge exposure, but lesions scores for pigs from vaccinated and control gilts were different (P < 0.01). CONCLUSIONS: Under these experimental conditions, immune-naive and vaccinated pigs from vaccinated gilts were protected against systemic lesions when challenge exposed with a virulent strain of H parasuis. CLINICAL RELEVANCE: Vaccination of the gilt and pigs protects the latter from polyserositis, but results are not different from those for nonvaccinated pigs from vaccinated gilts. Maternal antibodies did not seem to interfere with vaccination of pigs at 1 and 3 weeks of age.