Risk factors forSalmonellaseroconversion of fattening pigs in farrow-to-finish herds

Abstract

-We did a prospective observational 9-month long study to quantify risk factors of managerial and hygiene practices, and pig-health status for Salmonella seroconversion of fattening pigs reared in subclinically infected French farrow-to-finish farms. During the fattening phase, 2 649 pigs belonging to the same batch of contemporary pigs, from 89 conventional farrow-to-finish farms were individually followed and regularly blood sampled on a monthly basis. Farm recruitment was based on the farmer's willingness to cooperate. Pig status was assessed using an indirect ELISA test. Evolution of the serological status was studied by means of survival analysis. A Cox proportionalhazards model, taking into account the clustering of animals at the farm level, was used to examine the effects of explanatory variables on the time to Salmonella seroconversion of pigs. Applying group level antibiotic treatment to the pigs during the fattening period (Hazard Ratio (HR) = 2.4; 95% CI: 1.7, 3.4) was identified as a risk factor for Salmonella seroconversion, as the presence of residual Salmonella contamination in the fattening pen before placing the pigs into the pens (HR = 1.9; 95% CI: 1.2, 2.9). Porcine reproductive and respiratory syndrome virus (PRRSV) seropositivity during the fattening period also indicated an increased hazard for seroconversion (HR = 1.6; 95% CI: 1.1, 2.5). The batch size was identified as a risk factor for Salmonella seroconversion: the higher the number of pigs was in the fattening room followed, the higher was the risk (HR +10pigs = 1.05 for a 10-pig increment; 95% CI: 1.03, 1.06). The biosecurity measures of wearing specific clothes before entering the facilities (HR = 0.5; 95% CI: 0.3, 0.9) and enclosing the pig farm facilities were protective (HR = 0.4; 95% CI: 0.2, 0.8).Salmonella / pigs / seroconversion / risk factors / survival analysis

Pre-harvest risk factors for Salmonella enterica in pork production

“…However, due to a variety of potential confounding factors related to the intestinal microbial ecology in the host (i.e., the pigs), the susceptibility/resistance characteristics of the Salmonella strain present (or introduced) in the herd, and also to the dose and route of administration of the drugs, reported results are usually inconsistent, particularly when trying to determine the potential role of specific antibiotics as risk factor for Salmonella (Beloeil et al, 2007;Farzan et al, 2006;Funk et al, 2007;Funk, LeJeune, Wittum, & Rajala-Schultz, 2006;Hotes et al, 2010;Leontides et al, 2003;Rajic, Chow, et al, 2007;van der Wolf et al, 2001). On-farm antibiotic use is only one factor affecting bacterial resistance, which is also affected by several other on-farm factors that also influence the emergence of resistant foodborne pathogens, such as Salmonella (Farzan, Friendship, Dewey, Poppe, & Funk, 2010;Varga, Rajic, McFall, Reid-Smith, & McEwen, 2009).…”

“…In a field study, observed that seroconversion for L. intracellularis or for porcine reproductive and respiratory syndrome virus was associated with Salmonella shedding in finishing pigs. Moreover, Beloeil et al (2007) reported that seropositivity for porcine reproductive and respiratory syndrome virus was associated with a 1.6 (95% CI 1.1-2.5%) increased odds ratio for Salmonella seroconversion. Under experimental conditions, parasite infestation has also been shown to favor Salmonella infection and shedding in pigs (Steenhard et al, 2002).…”

“…However, according to Garcia-Feliz et al (2009), the odds ratio of a farm being Salmonella-positive was associated with its size; finishing units harvesting more than 3500 pigs per year had a higher risk for Salmonella shedding (OR = 1.78; 95% CI 0.96-3.31). In a study conducted by Beloeil et al (2007), large finishing batch size was identified as a risk factor for Salmonella seroconversion. Rajic, O'Connor, et al (2007) reported that finishing barns at multisite operations or individual grow-to-finish farms had a greater risk of the presence of Salmonella compared to finishing barns at farrow-to-finish farms.…”

Serological and bacteriological evaluation of Salmonella status in swine herds

“…The relationship between the high Salmonella seroprevalence in the sows and increased rate of the seropositive slaughtered fattening pigs in 2009 thus suggests an epidemiological link in the latently infected herds. This variation in serological findings may be potentially explained by the season, changes in hygiene level, management, and other risk factors in the herds which might have affected the course of Salmonella infection and seroconversion in fattening pigs (Beloeil et al 2007).…”

Parenteral administration of attenuated Salmonella Typhimurium ΔznuABC is protective against salmonellosis in piglets

“…Salmonellosis along with being a public health concern, is a economic problem as it also affects livestock breeding [3,4]. 26.9% of the human cases in the EU are caused by contaminated pork meat [5][6][7][8]. The prevalence of the main serovars in pigs, S. Typhimurium and S. Derby, is estimated approximately to be 10.3% at the slaughterhouse [6].…”