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

地方性猪繁殖与呼吸综合征病毒(PRRSV)传播的成本仅在美国猪群就估计为5.6亿美元/年。此外，PRRSV感染很难从单个牛群中预防、控制和消除。这导致了旨在从一个地区的所有畜群中消除PRR的倡议。由于初步成功，北美各地已经启动了几个这样的项目，包括在安大略省的一个项目。尽管有相当多的资源，但令人惊讶的是，在真实或模拟条件下评估区域战略方面所做的工作很少。实地评估区域消除策略的成本令人望而却步，该计划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不足。拟议研究的具体短期目标是：(I)开发和参数化PRRSV在一个地区传播的数学模型，(Ii)评估区域消除PRRSV的常见策略的有效性，以及(Iii)评估PRRSV和猪链球菌疫苗的直接、间接和总体效果。第一个目标将通过开发个人一级的数学模型来实现，该模型将根据从安大略省消灭PRRSV区域项目获得的数据构建。将使用纵向研究来进一步将该模型参数化。为此目的，将收集和分析经历PRRSV疫情的3个母猪群和3个肥育猪群的数据。这项工作将由一名理科学生完成。疫苗效力研究将用于评估现场条件下的直接、间接和总体疫苗效力。这将通过在苗圃阶段的多个猪场中使用PRRS病毒和猪链球菌自体疫苗接种不同比例的多个猪群来实现。死亡时间和发病率将使用考克斯回归进行分析，以评估疫苗的减弱效果。还将使用状态转换模型分析不同健康状态之间的转换。博士生将完成这项工作，估计将被用来提供消除PRRSV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.