AUTOGENOUS SALMONELLA TYPHIMURIUM MONOPHASIC VARIANT BACTERIN IS EFFECTIVE IN TWO ENDEMIC FARMS OF THE NORTH OF ITALY

Salmonella enterica serovar Typhimurium monophasic variant (S.T. 1,4,[5],12:i-) is increasingly responsible of human salmonellosis (EFSA, 2014) and pork represents the first source of infection. Salmonella can sub-clinically colonize pigs, principally during the finishing phase, and hence being introduced in the slaughterhouse, contaminating pork products destined to human consumption (Boyen et al., 2008). The biosecurity activities and management effectively decrease the prevalence in farms. However, other tools are envisaged for controlling Salmonella in endemic areas. Of these vaccination represents an efficient solution to decrease the infection in pig farms (Pesciaroli et al., 2013). Live vaccines are more effective than inactivated ones, inducing a cellular immune response that better enhances the clearance of Salmonella (Coward et al., 2014). The limitation is represented by the availability of attenuated vaccines whose protection versus different serovars, frequently diagnosed in pig farms, is not completely disclosed. In this scenario, immunization with autogenous bacterin could be more effective in endemic Salmonella farrowto-finish or multisite pig farms (Roesler et al., 2006).The efficacy of two autogenous vaccines versus S.T. 1,4,[5],12:i- was evaluated in two multisite pig production systems of the North of Italy. Forty sows were divided in vaccinated (V) or not vaccinated and intramuscular injection of 2x109 CFU/ml of inactivated S. Typhimurium 1,4,[5],12:i- was performed at 6 and 2 weeks before the delivery. Sixty piglets from sows of group V (three from each sow) were divided into 2 groups: vaccinated group (VV) and not vaccinated group (VnV). Also, the 60 piglets born from unvaccinated sows (nV) were divided in 2 groups: vaccinated group (nVV) and not vaccinated group (nVnV). Piglets were primed and boosted at 4 and 8 weeks after birth with the same immunization protocol of sows. Microbiological and serological exams of sows were performed during pregnancy and suckling phase, conversely, piglets were monitored throughout the production cycle. Data related to weight gain, fecal shedding of bacteria, organs colonization and humoral immune response were recorded. The results indicate that the administration of inactivated vaccines in breeding and/or growing phase is differently able to improve the growth of animals and hence the productivity of farms, and to reduce the load of bacteria carried into the food processing. Vaccination of sows does not affect Salmonella shedding in sows faeces, but tends to reduce the percentage of shedder piglets. Furthermore, the antibody titers of pigs born from vaccinated sows were reduced (V/V) or remained constant (V/nV) during the observational period, while antibody titers of pigs born from unvaccinated sows had a sharp increase close the slaughtering. Particularly, a combined vaccination of sows and their piglets is the best protocol to improve the weight gain of growing pigs, to limit Salmonella colonization of organs and to reduce carrier pigs.