Submitted to: Transboundary and Emerging Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2021
Publication Date: 7/8/2021
Citation: Stenfeldt, C., Bertram, M.R., Crocket, H., Hartwig, E.J., Smoliga, G.R., Niederwerder, M., Diel, D., Dee, S., Arzt, J. 2021. The risk and mitigation of foot-and-mouth disease virus infection of pigs through consumption of contaminated feed. Transboundary and Emerging Diseases. https://doi.org/10.1111/tbed.14230.
DOI: https://doi.org/10.1111/tbed.14230

Interpretive Summary: Import of animal feed and feed ingredients from other countries can lead to unintentional import of foreign pathogens, such as viruses. While there are many rules controlling imports of animals and animal-derived products, import of feed for animals is less controlled. This study investigated for how long foot-and-mouth disease virus (FMDV) could survive as a contaminant of commercial pig feed and some pig feed ingredients. An additional part of the investigation was to study how much FMDV was needed to cause foot-and-mouth disease (FMD) in pigs that ate contaminated feed. FMDV survival in feed and feed ingredients varied depending on virus strain, feed product, and storage temperature. FMDV survived longer in soybean meal compared to pelleted whole feed. The longest measured survival in soybean meal for two strains of FMDV was 37 days. The smallest amount of FMDV that caused disease in pigs was approximately 10^6 infectious doses. The ability of FMDV to cause infection in exposed pigs was prevented if the feed was treated with either of two commercially available feed additives, which were based on either formaldehyde (SalCURB®) or lactic acid (GuardianTM). Our findings demonstrate that FMDV may remain infectious in pig feed ingredients for durations such as import from countries overseas. These findings may be used to model the risk of FMDV import in feed, and to regulate feed importation to minimize the risk of unintentional importation.

Technical Abstract: Transboundary movement of animal feed and feed ingredients has been identified as a route for pathogen incursions. While imports of animals and animal-derived products are highly regulated for the purpose of infectious disease prevention, there has been less consideration of the viability of infectious agents in inanimate products, such as feed. This study investigated the ability of foot-and-mouth disease virus (FMDV) to remain infectious as a contaminant of commercial whole pig feed and select pig feed ingredients, and to establish the minimum infectious dose (MIDF) required to cause foot-and-mouth disease (FMD) in pigs that consumed contaminated feed. FMDV viability in vitro varied depending on virus strain, feed product, and storage temperature, with increased duration of infectivity in soybean meal compared to pelleted whole feed. The longest measured viability in soybean meal for two strains of FMDV was 37 days with storage at 4oC or 20oC . The MIDF for pigs consuming contaminated feed varied across virus strains and exposure duration in the range of 106.2 TCID50 - 107 TCID50. The ability of FMDV to cause infection in exposed pigs was mitigated by pre-treatment of feed with two commercially available feed additives, based on either formaldehyde (SalCURB®) or lactic acid (GuardianTM). Our findings demonstrate that FMDV may remain infectious in pig feed ingredients for durations compatible with transoceanic transport. Although the observed MIDF was relatively high, variations in feeding conditions and biophysical characteristics of different virus strains may alter the probability of infection. These findings may be used to parameterize modeling of risk of FMDV and to regulate feed importation to minimize the risk of inadvertent importation.