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Research Project: Susceptiblity of Pigs to FMD Infection via Natural Ingestion: Establishing Minimum Oral Infectious Dose and Evaluating...Mitigants

Location: Foreign Animal Disease Research

Project Number: 3022-32000-064-005-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Aug 1, 2018
End Date: Aug 1, 2021

Recent studies have demonstrated the ability of several important swine pathogens such as Senecavirus A [SVA], African Swine Fever Virus [ASFV], porcine epidemic diarrhea virus [PEDV], porcine reproductive and respiratory syndrome virus [PRRSV] among others, to remain infectious for up to 37 days in feed ingredients under transboundary shipping models simulating transportation of ingredients from Asia and/or Europe to the United States. These results provided direct evidence suggesting that contaminated feed ingredients may pose a risk for transboundary movement of pathogens of pigs and are likely to play a role in pathogen transmission at global and/or national level. This study will focus on the parameters of transmission of Foot-and-mouth disease virus (FMDV) by fomites, including contaminated feed. Research efforts will include; determination of minimum infectious dose (MID) of FMDV required to cause infection in swine when the virus is consumed naturally admixed within a food ration, the ability of FMDV to survive as a contaminant of commercial pig feed, as well as the potential beneficial effects of feed additives in inactivating the virus. Consultation with the research groups at South Dakota State University, Pipestone Applied Research, and Kansas State University will facilitate optimal experimental design and selection of feed additives that have been proven efficacious against closely related pathogens. Specific objectives of this research project include: 1: Determine the ability to recover infectious FMDV from contaminated feed. 2: Determine the MID of FMDV in pigs exposed by natural feeding of commercial pig feed (MFID) experimentally contaminated with pre-determined doses of FMDV. 3: Investigate the effect of mitigants in reducing infectivity of FMDV in commercial pig feed in vitro. 4: Investigate the ability of select feed additives in reducing infectivity of FMDV in feed in domestic pigs.

1: A series of controlled laboratory experiments will be carried out in order to investigate FMDV survival and viability in commercial pig feed. Small batches of commercial pig feed will be contaminated with known amounts of FMDV and incubated at room temperature. The ability to recover infectious virus and viral genome by virus isolation and qRT-PCR, respectively, will be assessed at time points ranging from 0 to 72 hours post contamination. 2: One initial animal experiment will be designed to determine the viral quantity required to infect pigs with FMDV through natural feeding behavior. Small batches of commercial pig feed will be spiked with pre-determined doses of the selected virus strain. Selection of FMDV quantities and the time delay from contamination of feed to feeding of pigs will be guided by the outcome of the initial in vitro experiments. Four groups of four pigs each will be housed in separate isolation rooms at PIADC. The separated groups will be provided one controlled feeding containing one of four virus doses: e.g. 104, 105, 106 or 107 TCID50. The pigs will be monitored for 14 days post exposure (dpe) for development of any clinical signs of FMD. Oropharyngeal swabs and serum will be collected daily from 0-10 dpe, and again at 14 dpe to assess any shedding or systemic dissemination of FMDV. Serum samples collected on 14 dpe will be used to assess seroconversion to FMDV. For animals that do not manifest clinical signs of FMD, necropsies will be performed at the termination of the experiment with harvest of oropharyngeal tonsils for detection of infectious virus and FMDV genome. The outcome of this experiment will guide the selection of virus doses to be used for in vivo experiments in objective 2. 3: Feed additives for mitigation of FMDV infectivity in pig feed will be selected based on previous experiments performed by the research groups at SDSU and KSU. Initial evaluation of the ability of these mitigants to reduce the infectivity of FMDV will be performed through controlled laboratory experiments. Feed will be contaminated with FMDV at doses established in objective 1-2. The selected mitigants will be added to the contaminated feed and the combined preparations will be incubated at room temperature for up to 3 days. The ability to recover FMDV from the feed preparations will be assessed by virus isolation and qRT-PCR after 1, 2, and 3 days of incubation, respectively. Experimental controls will consist of similarly prepared FMDV contaminated feed without added mitigant. 4: The outcome of in vitro mitigation study will guide selection of experimental conditions for subsequent trial in pigs. Feed will be spiked with FMDV at a dose rate range established in obj. 2 then in vitro mitigation study obj 3. Experimental groups will consist of 4 pigs that will be exposed to varying dose of virus as mitigants. All groups will be housed in separate isolation rooms and experimental procedures will be carried out as described in obj. 2.