A Farm Transmission Model for Salmonella in Pigs, Applicable to E.U. Member States

Abstract

The burden of Salmonella entering pig slaughterhouses across the European Union is considered a primary food safety concern. To assist E.U. member states with the development of national control plans, we have developed a farm transmission model applicable to all member states. It is an individual-based stochastic susceptible-infected model that takes into account four different sources of infection of pigs (sows, feed, external contaminants such as rodents, and new stock) and various management practices linked to Salmonella transmission/protection (housing, flooring, feed, all-in-all-out production). A novel development within the model is the assessment of dynamic shedding rates. The results of the model, parameterized for two case study member states (one high and one low prevalence) suggest that breeding herd prevalence is a strong indicator of slaughter pig prevalence. Until a member state's' breeding herd prevalence is brought below 10%, the sow will be the dominant source of infection to pigs raised for meat production; below this level of breeding herd prevalence, feed becomes the dominant force of infection.

Characterization of the Human Risk of Salmonellosis Related to Consumption of Pork Products in Different E.U. Countries Based on a QMRA

“…(j,k), but in this case the variation between simulations is larger than the effect of altering the value. [0.25,0.5, 1,2,3,4,5,6,7,8,9,10,12,14] Halving the storage…”

“…As stated previously, the exposure assessment modules are discussed in detail elsewhere. (4)(5)(6)(7) For clarity we provide a brief overview here. The Farm module describes the transmission of Salmonella infection between pigs on a farm.…”

“…A comprehensive description of the aims and processes of the risk assessment is presented elsewhere, (3) as are detailed descriptions of the methods used to estimate the prevalence and microbial load in the "exposure assessment" modules. (4)(5)(6)(7) In this article we describe how the likelihood of human salmonellosis due to pork consumption was estimated by integrating the output from the exposure assessment modules with a dose-response model in the simulation. The estimation is illustrated by the baseline results, and validation thereof, from four case study MSs chosen to represent different methods of pork production in the European Union.…”

Oral vaccination with a rough attenuated mutant of S. Infantis increases post-wean weight gain and prevents clinical signs of salmonellosis in S. Typhimurium challenged pigs

“…Our results are, therefore, promising but a much larger study, which takes in to account multi-variant effects, needs to be done before we can be more confident that pre-inoculation with S. Infantis 1326/28Ф r can inhibit or prevent shedding of S. Typhimurium in the immediate post-weaning period under conditions similar to those in the field. However, one study has suggested that the greatest risk factor for infecting piglets is the prevalence of Salmonella in the breeding herd and that the likelihood of transmission is high if the breeding herd prevalence is >10% (Hill et al 2015). It is therefore possible that oral inoculation with the candidate vaccine strain S. Infantis 1326/28Ф r could also be applied to the breeding herd to reduce Salmonella carriage in pregnant sows.…”

Livestock Health and Food Chain Risk Assessment

“…The third module ‘Food Production Exposure Assessment’ involved studying and properly running a ‘farm‐to‐consumption’ simulation to understand how the different basic processes of a quantitative microbiological risk assessment (QMRA) could be applied to modelling the variations in prevalence and concentration of a pathogen (Nauta, ). To this purpose, a QMRA was employed on ‘ Salmonella in Slaughter and Breeder Pigs’ developed for EFSA by a European Consortium led by APHA (Hill et al., ,b; Simons et al., ; Snary et al., ,b; Swart et al., ,b; Vigre et al., ,b). The model deals with four European countries and, as main output, it calculates the risk of human salmonellosis associated with the consumption of fresh pork cuts, minced meat and fermented sausage.…”