Sow vaccination modulates the colonization of piglets by Haemophilus parasuis.

Haemophilus parasuis is the etiologic agent of Glässer's disease in pigs and a colonizer of the upper respiratory tract of healthy pigs. A good balance between colonization and immunity is important to avoid a disease outbreak. This work studied the colonization of H. parasuis in healthy piglets coming from vaccinated and non-vaccinated sows. Piglets from vaccinated sows had higher IgG levels at early time points and subsequently were colonized later and to a lower degree than piglets from non-vaccinated ones. The variability of H. parasuis isolates was investigated by 2 genotyping methods: enterobacterial repetitive intergenic consensus (ERIC)-PCR and multilocus sequence typing (MLST). A high turnover of strains was found in both groups of piglets, with few strains found on more than one sampling occasion. We found a higher number of H. parasuis strains (16 strains) within a given farm than previously thought. Overall, more H. parasuis diversity was found in piglets from non-vaccinated sows than in those from vaccinated sows. These results indicate that vaccination of sows in a farm delays the colonization of piglets and reduces the carriage and heterogeneity of H. parasuis strains.