The Effectiveness of Commercial Vaccination against Lawsonia intracellularis in Mitigating the Reduction in ADWG, the Increased Mortality and Fecal Shedding of the Vaccinated Pigs: A Systematic Review and Meta-Analysis.

Abstract

Simple SummaryPorcine proliferative enteropathy (PPE), caused by Lawsonia intracellularis, is prevalent globally and produces a great economic impact on affected countries. However, its pathogenic mechanism has not been completely elucidated as the infectious agent is an anaerobic obligate intracellular bacterium, which has resulted in considerable difficulty for controlling the disease. Two commercial vaccines for controlling PPE are currently available, and a systematic review and meta-analysis were performed to assess the pooled effect of the vaccines to provide updated quantitative evidences to the stakeholders. The efficacy of the vaccines was assessed using three outcomes: average daily weight gain (ADWG), mortality, and fecal shedding. The results indicated that the vaccinated pigs showed significantly reduced risk in mortality and fecal-shedding compared to the control pigs. The significant increase in ADWG was also observed in the immunized pigs compared to the unvaccinated controls. Considering the current situation that new alternatives for control of PPE is not identified, these evidence-based findings will help improve decision-making on practical use of the vaccines to prevent PPE. Furthermore, the results will also provide updated information to the researchers while experimental candidate vaccines against PPE are being developed. In this study, a systematic review and meta-analysis was conducted to assess the efficacy of commercial vaccines against PPE in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist. Of the 373 articles reviewed, 16 fulfilled the pre-specified inclusion criteria. Three independent reviewers extracted the data, and vaccine effectiveness was assessed using the outcomes of interest. The majority of studies had a low or unclear risk of bias as assessed using the ARRIVE guidelines. The results of the meta-analysis indicated that the vaccination resulted in statistically significant reductions in bacterial fecal shedding (odds ratio, OR = 0.122, 95% confidence interval, CI 0.054–0.278) and mortality rate (risk ratio, RR = 0.199; 95% CI, 0.066–0.605). Furthermore, ADWG was significantly increased in the vaccinated pigs compared to the unvaccinated controls (standardized mean difference (SMD) = 0.606, 95% CI 0.243–0.969). In the subgroup analysis, the production phase and study type significantly influenced the effect size (p < 0.1). The Egger’s regression test showed no evidence of publication bias (p > 0.1). The effectiveness of commercially available vaccines against PPE-related weight loss, fecal shedding, and mortality suggests that the vaccines may help control PPE on affected swine farms.