Efficiency evaluation of a novel orally administered subunit vaccine to reduce the prevalence of Salmonella enterica in swine under field conditions

Salmonella enterica can be carried by pigs and can reach the final product and the consumer. Thus, Salmonella reduction strategies along the swine production chain should be studied. In this sense, the objective of the study was to evaluate a subunit vaccine based on secondary antigens administered orally against natural infection in swine farms in Brazil. A field trial study was conducted to estimate the effect of the vaccination on the Salmonella spp. seroprevalence, presence in lymph nodes, and fecal content in commercial pig herds in a vertical integration system belonging to an agroindustry. Furthermore, nMPN, qPCR, and phagocytic activity were performed. There were no significant differences in seroprevalence between groups. The mMPN count of Salmonella spp. in feces was higher in vaccinated group (VG), ranging from 0 to 2.46 log mMPN/g, while in control group (CG) it ranged from 0.0 to 4 log mMPN/g, showing a significant group effect (p<0.05), being confirmed in the qPCR. The activity of phagocytic monocytes was not altered by vaccination on farms. Thus, the oral subunit vaccination strategy at this stage of development did not reduce the spread and amplification of the infection in farms that would impact the prevalence of pigs carrying and shedding Salmonella spp. until slaughter.