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）传播的成本就为5.6亿美元/年。此外，PRRSV感染难以从个体畜群中预防、控制和消除。这导致了旨在从一个地区的所有牛群中消除PRRS的举措。由于初步成功，在北美各地发起了几个这样的项目，包括在安大略的项目。尽管有相当多的资源，在真实的或模拟条件下评价区域战略的工作却少得令人吃惊。区域消除战略的实地评估是成本高昂的，这个计划的目的是通过评估不同的区域消除战略在模拟条件下的效果，以填补这方面的知识缺乏。具体的短期目标，拟议的研究是：（一）建立和参数化的数学模型，在一个地区的传播，（二）评估的有效性，区域消除的PRRSV的共同战略，和（三）估计直接，间接和整体的效力，疫苗的PRRSV和猪链球菌。第一个目标将通过开发个体水平的数学模型来实现，该模型将基于从区域安大略PRRSV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式。为此目的，将收集和分析3个母猪群和3个育肥育猪群经历PRRSV爆发的数据。这项工作将由一名理学硕士学生完成。疫苗效力研究将用于估计田间条件下的直接、间接和总体疫苗效力。这将通过在保育期的多个养猪场使用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完成。将使用考克斯回归分析至死亡和发病的时间，以估计疫苗的减弱效应。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，估计将用于通知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.