Location: Foreign Animal Disease Research2012 Annual Report
1a. Objectives (from AD-416):
The goal of this research project is to determine if pigs are competent hosts to maintain persistent infection with Foot-and-Mouth Disease virus (FMDV). Specific objectives include: (1) Determine optimal route of direct inoculation of donor pigs for contact experiments through the comparison of inoculation routes. (2) Characterize FMDV acute pathogenesis parameters of infection in contact transmission studies using FMDV serotype O. (3) Characterize FMDV post-acute pathogenesis parameters of infection in contact transmission studies using FMDV, serotype O. (4) Characterize FMDV chronic pathogenesis parameters of infection in contact transmission studies using FMDV serotypes A and Asia 1.
1b. Approach (from AD-416):
(1) A comparative study to determine the efficacy of intra-oral and heel bulb-intradermal FMD inoculation as administration route using FMDV serotype O. Determine tissue tropism of FMDV during acute disease in pigs through time-course study which will include transmission experiments. Sample tissues will be screened for presence of FMDV and further by immunomicroscopy. (2) Similar to above, studies will be conducted to determine if pigs, which are allowed to survive acute FMD infection, subsequently become chronic asymptomatic carriers/shedders. Tissues collected in late stage infection will be analyzed for the presence of FMDV. (3) Pigs in post-acute phase will be tested for their ability to transmit FMDV serotype O to naïve pigs through contact exposure. (4) Similar transmission studies will be conducted using serotypes A and Asia 1.
3. Progress Report:
This research project seeks to define scientific documentations regarding the lack of a Foot-and-Mouth Disease (FMD) carrier state in pigs that could form the basis for promoting species-specific FMD outbreak mitigation policies. This information will contribute to rational design of swine-specific vaccines, biotherapeutics and diagnostic tools. During FY 2012 we conducted initial experimental studies including optimization of novel systems for intra-oral (IO) and intra-nasal (IN) inoculation of swine with FMDV serotype O. Results indicate that the IO system produces reproducible and highly synchronized clinical infection, with a high degree of similarity between individual animals. This IO inoculation system utilizes a more natural route of virus exposure in comparison to the commonly used techniques of inoculation through direct injection of virus into the heel bulb of the animals. This optimized system is therefore valuable for studies investigating the pathogenesis of acute and post-acute FMDV infection in pigs. Tissue samples obtained from necropsies of pigs during acute (24-48 hours post infection), as well as late (35 days post infection) phases of infection have been analyzed for the presence of FMDV using a trimodal FMDV detection strategy of virus isolation, RT-PCR, immunomicroscopy. Preliminary findings from these initial investigations have indicated that some swine tissues contain FMDV RNA up to 35 days post inoculation (dpi), but no infectious FMDV has been recovered. No technologies were transferred or publications have been prepared in FY 2012.