Identifying Active Salmonella Infections in Swine Nurseries Using Serology and Bacterial Culture and Evaluating Associated Risk Factors

Abstract

The objectives of this study were: to identify nursery cohorts with an active Salmonella infection using combined serological and bacteriological methods, and to try to identify risk factors associated with swine nurseries with active Salmonella spread. Twenty pigs from each of 50 cohorts of weaned pigs from 44 different nursery barns were sampled about the time of weaning and near the end of the nursery stage. Information regarding farm management and biosecurity practices were collected using a questionnaire. Blood samples were obtained at both visits, while rectal swabs were collected at the second visit. An enzyme-linked immunosorbent assay (ELISA) was used to test sera for Salmonella antibodies and rectal samples were cultured for Salmonella. A nursery cohort was identified as having an active Salmonella infection if Salmonella was cultured from one or more of the 20 pigs or if serological evidence suggested exposure to Salmonella. The association between farm-level management covariates and active Salmonella infection was assessed in 46 cohorts using a logistic regression model. Nine of 46 (20%) cohorts produced Salmonella-free pigs. The remaining 37 (80%) cohorts were classified as having an active infection. Examination of risk factors failed to identify how negative and positive nurseries differed.

Salmonella Infection in Nursery Piglets and Its Role in the Spread of Salmonellosis to Further Production Periods

“…No differences were found regarding serological OD% values between infected and non-infected piglets (median OD% of 4.7 and 4.8, respectively), these values being similar to those found in piglets of the same age in other studies [ 20 ]. However, on average, OD% values were much lower than those found in the previous study on 4-wo piglets from the same farms (15.9%; [ 16 ]), evidencing the likely significant decay of maternally derived IgGs against Salmonella within the two weeks after weaning [ 7 ]. It seems that the beginning of the nursery may be a period of high susceptibility to the infection and that measures to prevent exposure to Salmonella should be encouraged at this time.…”

“…A similar proportion of piglets (37.3%; 95% CI 32.6–42.2) could be considered Salmonella shedders as the bacterium was found in their IC ( Table 1 ). Few field studies have been carried out on Salmonella prevalence at this stage, and when performed through the sampling of live piglets, results suggested active infection but the recovery levels of fecal Salmonella were usually much lower [ 7 , 17 ]. Two major issues would help to understand the differences between this and previous studies.…”

“…Since the presence of Salmonella during the growing–finishing phase is directly related to carcass contamination at abattoirs, main mitigation measures have been usually directed toward this production period [ 3 , 4 , 5 , 6 ]. However, few studies have focused on the periods previous to this one, such as the nursery, although active Salmonella infections have been identified in pig nurseries [ 7 ].…”

Monophasic Variant of Salmonella Typhimurium Infection Affects the Serum Metabolome in Swine

“…This is in line with the European strategy to optimize food safety [1]. However, identification of the infected animals or highly shedding animals in the first steps of the production is limited [3,8] because the carriage and shedding of Salmonella in swine are mostly asymptomatic and intermittent, and the collection of individual feces and detection of Salmonella by classical methods are fastidious.…”