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 select 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.
Laboratory experiments were designed to study for how long FMDV remained infectious when added to pelleted whole pig feed blend, soybean meal, and distiller’s dried grains with soluables (DDGS). A known amount of virus was added to samples of the specific ingredients, and the amount of virus that could be recovered was measured after storage of samples at 4oC (refrigerated) or 20oC (room temperature) for up to 37 days.
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 while the virus was quickly inactivated when added to DDGS. The longest measured survival in soybean meal for two strains of FMDV was 37 days at either storage temperature.
Additional experiments consisted of feeding 12-week-old pigs portions of pelleted whole feed that had been contaminated with known amounts of FMDV.
The smallest amount of FMDV that caused disease in pigs ranged from 10^6.2 TCID50 – 10^7 TCID50, depending on both virus subtype and feeding conditions (duration of exposure). The ability of FMDV to cause infection in exposed pigs was prevented if the feed was treated with either of two commercial 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 compatible with import from countries overseas. Although the amount of virus that was needed to make pigs sick was relatively high, variations in feeding conditions and characteristics of different variants of FMDV may change the likelihood of infection. 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.
- Foot-and-mouth disease can remain viable as a contaminant of pig feed and pig feed ingredients for at least 37 days
- The duration of infectiousness of FMDV depends on both intrinsic virus properties (virus strains), storage matrix, and temperature
- Relatively high doses of FMDV are required to cause foot-and-mouth disease in pigs consuming contaminated feed
- The minimum infectious dose of FMDV through contaminated feed depends on virus strain and feeding conditions (exposure duration)
- FMDV can be inactivated by select feed additives (formaldehyde- or lactic acid based products)