Evaluation of Haemophilus parasuis control in the nursery using vaccination and controlled exposure

Objective: To evaluate the effectiveness of three control measures in reducing nursery mortality caused by Haemophilus parasuis, namely, a commercial vaccine, an autogenous vaccine, and controlled exposure using a low dose of live, virulent organisms. Methods: The experiments were performed in a multi-farm system experiencing high nursery mortality (> 4.8%) due to H parasuis infection. In Experiment 1, pigs were vaccinated at weaning using a commercially available, one-dose H parasuis vaccine. In Experiment 2, pigs were vaccinated at processing and at weaning with an autogenous vaccine. In Experiment 3, pigs were orally inoculated at processing using a bacterial suspension containing a total of 10^5-6 colony forming units per mL of three H parasuis strains prevalent in the studied herd. Experiments 1 and 2 were repeated five times (5 consecutive weeks of production), and Experiment 3 was repeated nine times. Results: Mortality in pigs exposed to H parasuis was lower (P < .001) than that in groups vaccinated with either commercial or autogenous vaccines. Discussion: The lack of effect of parenteral vaccination may be due to lack of cross-protection between heterologous strains, timing of vaccination, and potential interference of maternally-derived immunity. The efficacy of controlled exposure likely reflects the induction of homologous mucosal immunity preventing pathogen systemic invasion. Implications: The use of controlled exposure of young pigs to the prevalent H parasuis strains involved in nursery mortality provides a valuable alternative for control of H parasuis, compared to traditional vaccination using commercial or autogenous products.