Protective role of maternal antibodies against Haemophilus parasuis infection

Objective-To evaluate the impact of maternal antibodies after challenge exp osure 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 conta ined 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 V accinated gilts were evaluated for clinical signs of infection, lesions, an d antibody titer. Results-All pigs coming from control gilts had severe signs of H parasuis i nfection. Macroscopic lesions included polyserositis and pneumonia, and bac teriologic examination confirmed H parasuis as the etiologic agent. Vaccina ted pigs born to vaccinated gilts did not have clinical signs of disease. H owever, some vaccinated pigs born to control gilts had signs of nervous sys tem dysfunction and lameness. There was no difference in lesion scores betw een early or late challenge exposure, but lesions scores for pigs from vacc inated and control gifts were different (P < 0.01). Conclusions-Under these experimental conditions, immune-naive and vaccinate d pigs from vaccinated gifts were protected against systemic lesions when c hallenge exposed with a virulent strain of H parasuis. Clinical Relevance-Vaccination of the gilt and pigs protects the latter fro m 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.