Serological evaluation of vaccination against Salmonella Typhimurium with an attenuated vaccine in two farrow-to-finish farms

Pig herds are frequently infected with Salmonella Typhimurium. Infections are mostly subclinical and difficult to control with the currently available control measures. Vaccination might be effective to control Salmonella infections at farm level and hence be a promising tool to reduce the risk for human salmonellosis.

In this study, five different vaccination strategies (1. vaccination of sows; 2. vaccination of sows and piglets; 3. vaccination of sows and fatteners; 4. vaccination of piglets; 5. vaccination of fatteners) were tested and compared to a negative control group (group 6) in two Belgian farrow-tofinish farms. Seventy-two (72) sows of one batch were divided into six groups (12 sows/group) and the pigs were followed until slaughter. An attenuated vaccine (Salmoporc®, IDT Biologika) was applied twice, each time with an interval of three weeks. The vaccine was administered subcutaneously in sows and fatteners and orally in piglets. Blood samples were collected before and after vaccination to evaluate the serological response of vaccination. The sera were analyzed by ELISA and the sample-to-positive-ratios (S/P-ratio) were assessed.

Prior to vaccination, the mean S/P-ratio of the sows in group 1-3 and the sows in group 4-6 did not differ (farm 1: 1.448 and 1.398, p=0.876 – farm 2: 1.046 and 0.669, p=0.312). Three days after farrowing, the mean S/P-ratio of the vaccinated sows (group 1-3) was significantly higher than the mean S/P-ratio of the non-vaccinated sows (group 4-6) (farm 1: 2.525 and 1.111, p< 0.001 – farm 2: 2.313 and 0.493, p< 0.001). At three days of age, piglets from vaccinated sows had a significantly higher mean S/P-ratio compared to piglets from non-vaccinated sows (farm 1: 2.674 and 1.333, p< 0.001 – farm 2: 2.685 and 0.399, p< 0.001). A high Pearson-correlation between the S/P-ratios of the sows and the S/P-ratios of the piglets was found on both farms (farm 1: 0.934 – farm 2: 0.953, p< 0.001).

At slaughter age, the S/P-ratios of the vaccinated pigs (group 1-5) did not significantly differ from the S/P-ratios of the negative control group on farm 2. In farm 1, the S/P-ratios of the vaccinated fatteners (group 3 and 5, means: 2.130 and 3.489) were significantly higher compared to the S/P-ratios of the control group (mean: 1.240, p=0.041 and p=0.016).

Vaccination of sows induces a serological response and increases the degree of maternal immunity, which is transferred from the sow to the piglets.

The high S/P-ratios of the vaccinated fatteners can be explained by the immune response induced by the vaccination and show that vaccination of fatteners might influence the results of serological monitoring programs currently in use.

Disclosure of Interest: None Declared.