Detection of Salmonella antibodies in the saliva of pigs from Salmonella Typhimurium-vaccinated and unvaccinated herds

This study aimed to investigate the oral fluid saliva (OF) collected passively via chewed sampling ropes as a potential sample type for assessing anti-Salmonella antibodies in 2 Salmonella-vaccinated (V) and 2 non- vaccinated (NV) pig farms, comparing the results with direct bacteriological diagnostic methods. Gilts and sows in the V farms were vaccinated prior to farrowing with a live attenuated vaccine (Salmoporc STM - IDT Biologika). For each age class (sows - S, weaners - W and grower pigs – G) pooled of faecal and OF samples were collected. Salmonella was isolated according to a modification of ISO6579 Annex D. In parallel, IgG antibody titres were assessed in OF samples using an ELISA assay (IDEXX Swine Salmonella Ab Test - IDEXX Laboratories). Salmonella was detected in 90.6% of faecal samples in NV farms, and in 36.1% of V farms (p<0.001). A lower prevalence (47.8%) was observed in W+G of V farms compared to 97.1% in NV farms. In V farms, the IgG levels in OF were higher in S and declined in W+G. In NV farms, W+G had higher IgG levels than S. The lower Salmonella prevalence in S of V farms probably correlates with the higher antibody titer, which was lower in weaners and growers. Antibodies measured in V farms are likely to be partially related to vaccination. Conversely, in NV farms a high IgG antibody titre was observed in W+G and correlated with high level of shedding, suggesting that the antibody response was related to infection with field Salmonella strains. The use of OF to assess antibodies in pigs represents a valid alternative to serum. However, to assess vaccination efficacy in stimulating antibody response, further studies are necessary to discriminate between IgG produced in response to vaccination and that resulting from infection with field Salmonella strains.