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

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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.