Efficacy of Vaccination to ReduceSalmonellaPrevalence in Live and Slaughtered Swine: A Systematic Review of Literature from 1979 to 2007

Abstract

A systematic review was conducted to evaluate the efficacy of vaccination to reduce Salmonella prevalence in market weight finisher swine. A search of online databases and selected conference proceedings was conducted to identify relevant studies. The review process followed relevance screening, methodological quality assessment, and data extraction. Although multiple outcomes were frequently reported, only outcomes describing culture of Salmonella were extracted. Five clinical trials and 23 challenge studies were considered likely relevant to the review as they described vaccination to reduce Salmonella in swine. Five clinical trials reported vaccination was associated with reduced isolation of Salmonella in market weight pigs, however, information required to assess the internal validity of the study was often not described in the manuscripts. All challenge studies assessed vaccine efficacy in pigs aged <15 weeks reducing the relevance of results to the review which focused on market weight pigs. Only five of the 23 challenge studies reported the majority of information necessary to evaluate the quality of vaccine studies. Given large variability in population type, sample size, type of vaccine, dose and dosing regimens, and type of outcomes observed, pooled data analysis was not possible, and therefore, a qualitative synthesis of the studies was conducted. Available evidence suggests that vaccination is associated with reduced Salmonella prevalence in swine at or near harvest; however, this conclusion is based on studies with design and reporting deficiencies that could potentially indicate biases with the outcome.

The REFLECT Statement: Reporting Guidelines for Randomized Controlled Trials in Livestock and Food Safety: Explanation and Elaboration

“…These trials lacked information related to the method of treatment allocation, the grouping of animals relative to treatment allocation, the use or non-use of blinding and the method of statistical analysis (Elbers and Schukken, 1995). Further, several systematic reviews in pre-harvest food safety (Denagamage et al, 2007;O'Connor et al, 2008) and animal health (O'Connor et al, 2006;Wellman and O'Connor, 2007;Burns and O'Connor, 2008) have noted a lack of reporting of group allocation methods; blinding and details related to intervention protocols, outcome assessments and statistical analysis methods in some published clinical trials. This lack of consistency in reporting makes it almost impossible to summarize sufficient data appropriately, thereby affecting the ability to arrive at an overall conclusion on a particular intervention or outcome.…”

Mathematical Modeling of the Transmission and Control of Foodborne Pathogens and Antimicrobial Resistance at Preharvest

“…To model imperfect vaccines, animals are classified based on both their epidemiological and vaccination status (e.g., susceptible and susceptible vaccines) and the vaccine effects are explicitly included in the model. Several studies indicate that available Salmonella vaccines are imperfect (Zhang-Barber et al, 1999;House et al, 2001;Denagamage et al, 2007;Heider et al, 2008). For example, some vaccines decrease susceptibility to infection, whereas others shorten the infectious period or reduce fecal shedding.…”

Evaluation of three intervention strategies to reduce the transmission of Salmonella Typhimurium in pigs

“…In most studies the use of Salmonella Typhimurium vaccines significantly decreased clinical signs and excretion of Salmonella (Springer et al, 2001;Roesler et al, 2004Roesler et al, , 2006Eddicks et al, 2009;Farzan and Friendship, 2010;Hotes et al, 2011;Hur et al, 2011). However, Denagamage et al (2007) concluded in their review that the design and reporting deficiencies in many studies (e.g. little detail on population type, sample size, type of vaccine, dose and dosing regimens) meant that the association between vaccination and Salmonella reduction in finisher swine was promising, but not proven.…”