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United States Department of Agriculture

Agricultural Research Service

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Location: Foreign Animal Disease Research

2013 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. Finalized ongoing experiments with the objective of developing and optimizing novel simulated natural FMDV exposure systems for pigs. Experimental studies evaluating intra-orophasyngeal (IOP) and intra-nasopharyngeal inoculation of swine using FMDV serotype A were performed to extend the data previously generated during similar experimental studies using FMDV serotype O. The results of these initial experimental studies suggest that the newly developed IOP inoculation system is preferred and advantageous for studies of FMDV pathogenesis in swine. The potential for pigs to serve as hosts for persistent FMDV infection has been investigated through experimental studies with FMDV serotypes O, A, and Asia-1. Preliminary findings indicate that it is not possible to isolate infectious virus from porcine tissues during the late phase of infection (>28 days post infection). There is, however, a relatively high prevalence of retained FMDV degradation products, consisting of RNA and capsid antigen, in lymph nodes that drain specific lesion sites. The significance of these byproducts is unclear at this time. Continued investigations of the acute pathogenesis of FMDV in pigs have been performed through time course experiments investigating viral dynamics and tissue distribution of virus in animals that have been euthanized at pre-determined time points from 6 to 72 hours post infection with FMDV serotype O and A. Analysis of samples obtained from performed animal studies is currently ongoing and will continue through November 2013 when this grant will expire. The outcome of this work will guide further efforts within this research objective. No technologies have been transferred or publications produced during FY 2013.

4. Accomplishments

Last Modified: 06/22/2017
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