Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
J Theor Biol. 2009 Aug 21;259(4):770-84. doi: 10.1016/j.jtbi.2009.04.028. Epub 2009 May 14.
Salmonella spp. in cattle contribute to bacterial foodborne disease for humans. Reduction of Salmonella prevalence in herds is important to prevent human Salmonella infections. Typical control measures are culling of infectious animals, vaccination, and improved hygiene management. Vaccines have been developed for controlling Salmonella transmission in dairy herds; however, these vaccines are imperfect and a variety of vaccine effects on susceptibility, infectiousness, Salmonella shedding level, and duration of infectious period were reported. To assess the potential impact of imperfect Salmonella vaccines on prevalence over time and the eradication criterion, we developed a deterministic compartmental model with both replacement (cohort) and lifetime (continuous) vaccination strategies, and applied it to a Salmonella Cerro infection in a dairy farm. To understand the uncertainty of prevalence and identify key model parameters, global parameter uncertainty and sensitivity analyses were performed. The results show that imperfect Salmonella vaccines reduce the prevalence of Salmonella Cerro. Among three vaccine effects that were being considered, decreasing the length of the infectious period is most effective in reducing the endemic prevalence. Analyses of contour lines of prevalence or the critical reproduction ratio illustrate that, reducing prevalence to a certain level or zero can be achieved by choosing vaccines that have either a single vaccine effect at relatively high effectiveness, or two or more vaccine effects at relatively low effectiveness. Parameter sensitivity analysis suggests that effective control measures through applying Salmonella vaccines should be adjusted at different stages of infection. In addition, lifetime (continuous) vaccination is more effective than replacement (cohort) vaccination. The potential application of the developed vaccination model to other Salmonella serotypes related to foodborne diseases was also discussed. The presented study may be used as a tool for guiding the development of Salmonella vaccines.
牛源沙门氏菌会导致人类食源性疾病。降低牛群中沙门氏菌的流行率对于预防人类沙门氏菌感染非常重要。典型的控制措施包括淘汰感染动物、接种疫苗和改善卫生管理。已经开发出用于控制奶牛群中沙门氏菌传播的疫苗；然而，这些疫苗并不完美，并且报告了各种疫苗对易感性、传染性、沙门氏菌脱落水平和传染性持续时间的影响。为了评估不完美的沙门氏菌疫苗对随时间推移的流行率和根除标准的潜在影响，我们开发了一个具有替换（队列）和终生（连续）疫苗接种策略的确定性隔室模型，并将其应用于一个奶牛场的沙门氏菌 Cerro 感染。为了了解流行率的不确定性并确定关键模型参数，进行了全局参数不确定性和敏感性分析。结果表明，不完美的沙门氏菌疫苗可降低沙门氏菌 Cerro 的流行率。在所考虑的三种疫苗效果中，缩短传染性期是降低地方性流行率最有效的方法。流行率或临界繁殖比的等高线分析表明，通过选择具有相对较高效果的单一疫苗效果或具有相对较低效果的两种或更多疫苗效果的疫苗，可以将流行率降低到一定水平或零。参数敏感性分析表明，应根据感染的不同阶段调整通过应用沙门氏菌疫苗进行有效控制的措施。此外，终生（连续）接种比替换（队列）接种更有效。还讨论了开发的疫苗接种模型在其他与食源性疾病相关的沙门氏菌血清型中的潜在应用。提出的研究可以用作指导沙门氏菌疫苗开发的工具。
