Design and evaluation of disease control and elimination strategies from swine populations

据估计，仅在美国猪群中，地方性猪繁殖与呼吸综合征病毒（PRRSV）传播的成本为每年5.6亿美元。此外，PRRSV感染难以在单个畜群中预防、控制和消除。这导致了旨在从一个地区的所有畜群中消除PRRS的倡议。由于初步的成功，在北美各地开始了几个这样的项目，包括在安大略的项目。尽管资源相当可观，但令人惊讶的是，在真实或模拟条件下对区域战略进行评估的工作很少。区域消除策略的现场评估成本过高，本项目旨在通过在模拟条件下评估不同区域消除策略的有效性来填补这一知识的不足。拟建研究的具体短期目标是：(i)建立一个地区PRRSV传播的数学模型并将其参数化；（ii）评估区域消灭PRRSV的通用策略的有效性；（iii）评估PRRSV和猪链球菌疫苗的直接、间接和总体有效性。第一个目标将通过开发个人层面的数学模型来实现，该模型将根据从安大略省PRRSV区域消除项目获得的数据构建。纵向研究将用于进一步参数化这一模型。为此目的，将收集和分析发生PRRSV疫情的3个母猪群和3个育肥猪群的数据。这项工作将由一名硕士生完成。疫苗效力研究将用于估计实地条件下疫苗的直接、间接和总体效力。这将通过在苗圃阶段的多个养猪场中使用PRRS病毒和猪链球菌的自体疫苗接种不同比例的多个猪群来实现。死亡率和发病率的时间将使用Cox回归分析，以估计疫苗的减弱效应。还将使用状态转换模型分析不同运行状况状态之间的转换。博士生将完成这项工作，估计结果将用于建立PRRSV消除的数学模型。

Cost of endemic porcine reproductive and respiratory syndrome virus (PRRSV) circulation has been estimated at $560 million/year in the US swine population alone. In addition, PRRSV infection is difficult to prevent, contain, and eliminate from individual herds. This led to initiatives aiming to eliminate PRRS from all herds in a region. Owing to initial success, several such projects have been initiated across North America, including the one in Ontario. Despite considerable resources, surprisingly little work has been done in evaluation of regional strategies under real or simulated conditions. Field evaluation of regional elimination strategies is cost prohibitive, and this program aims to fill this lack of knowledge by evaluating efficacy of different regional elimination strategies under simulation conditions. Specific short-term objectives of the proposed research are: (i) To develop and parametrize mathematical model of PRRSV transmission in a region, (ii) To evaluate efficacy of common strategies for regional elimination of PRRSV, and (iii) To estimate direct, indirect, and overall efficacy of vaccines for PRRSV and for Streptococcus suis. The first objective will be fulfilled by development of the individual level mathematical model that will be constructed based on data obtained from the regional Ontario PRRSV elimination project. Longitudinal studies will be used to further parametrize this model. Data from 3 sow herds and 3 finisher herds experiencing PRRSV outbreaks will be collected and analyzed for this purpose. This work will be done by an MSc student. Vaccine efficacy studies will be used to estimate direct, indirect and overall vaccine efficacy under field conditions. This will be done by vaccinating different proportions of multiple swine populations using autogenous vaccines for PRRS virus and Streptococcus suis in multiple swine operations during nursery phase. Time to mortality and morbidity will be analyzed using Cox's regression to estimate a waning effect of vaccines. Transition between different health states will also be analyzed using state transition models. PhD student will complete this work and estimates will be used to inform the mathematical model of PRRSV elimination.