Viruses of veterinary significance such as African swine fever virus, are known to survive for extended periods in plant-based feed ingredients imported into North America. To reduce the likelihood of virus introduction, high-risk ingredients, such as oil seed meals, are stored in designated facilities for extended periods under controlled environmental conditions to minimize viral infectivity prior to use in diets. While 30 days has become a standard storage period, the required ambient temperature to inactivate viruses during this time is not known. To address the question, 1-metric ton totes of conventional soybean meal were inoculated with PRRSV 144 lineage 1C variant and SVA prior to storage for 30 days at 23.9º C, 15.5º C, or 10º C, and feeding to pigs. Virus infectivity was evaluated through detection of viral RNA in oral fluid samples, along with clinical signs. Results indicated that inactivation of both viruses occurred in soy stored at 23.9º C. In contrast, SVA infectivity was observed in soy stored at both 15.5º C and 10º C, while PRRSV 144 L1C variant infectivity was only observed in soy stored at 10º C. These results suggest that a storage period of 30-days and a temperature of 23.9º C are required to reduce the risk of virus contaminated plant-based feed ingredients, such as soybean meal.

The hypothesis that feed ingredients could serve as vehicles for the transport and transmission of viral pathogens was first validated under laboratory conditions. To bridge the gap from the laboratory to the field, this current project tested whether three significant viruses of swine could survive in feed ingredients during long-distance commercial transport across the continental US. One-metric ton totes of soybean meal (organic and conventional) and complete feed were spiked with a 10 mL mixture of PRRSV 174, PEDV, and SVA and transported for 23 days in a commercial semi-trailer truck, crossing 29 states, and 10,183 km. Samples were tested for the presence of viral RNA by PCR, and for viable virus in soy-based samples by swine bioassay and in complete feed samples by natural feeding. Viable PRRSV, PEDV, and SVA were detected in both soy products and viable PEDV and SVA in complete feed. These results provide the first evidence that viral pathogens of pigs can survive in representative volumes of feed and feed ingredients during long-distance commercial transport across the continental US.

African swine fever virus (ASFV) can survive in soy-based products for 30 days with T ½ ranging from 9.6-12.9 days in soybean meals and soy oil cake. As the US imports soy-based products from several ASFV-positive countries, knowledge of the type and quantity of these specific imports, and their ports of entry (POE), is necessary information to manage risk. Using the data from the International Trade Commission Harmonized Tariff Schedule website in conjunction with pivot tables, we analyzed imports across air, land, and sea POE of soy-based products from 43 ASFV-positive countries to the US during 2018 and 2019. In 2018, 104,366 metric tons (MT) of soy-based products, specifically conventional and organic soybean meal, soybeans, soy oil cake and soy oil were imported from these countries into the US via seaports only. The two largest suppliers were China (52.7 %, 55,034 MT) and the Ukraine (42.9%, 44,775 MT). In 2019, 73,331 MT entered the US and 54.7% (40,143 MT) came from the Ukraine and 8.4% (6,182 MT) from China. Regarding POE, 80.9% to 83.2% of soy-based imports from China entered the US at the seaports of San Francisco, CA and Seattle, WA, while 89.4% to 100% entered from the Ukraine via the seaports of New Orleans, LA and Charlotte, NC. Analysis of five-year trends (2015 to 2019) of the volume of soy imports from China indicated reduction over time (with a noticeably sharp decrease between 2018 and 2019), and seaport utilization was consistent. In contrast, volume remained high for Ukrainian soy imports, and seaport utilization was inconsistent. Overall, this exercise introduced a new approach to collect objective data on an important risk factor, providing researchers, government officials, and industry stakeholders a means to objectively identify and quantify potential channels of foreign animal disease entry into the US.

The role of animal feed as a vehicle for the transport and transmission of viral diseases was first identified during the porcine epidemic diarrhea virus (PEDV) epidemic in North America. Since that time, various feed additives have been evaluated at the laboratory level to measure their effect on viral viability and infectivity in contaminated feed using bioassay piglet models. While a valid first step, the conditions of these studies were not representative of commercial swine production. Therefore, the purpose of this study was to evaluate the ability of feed additives to mitigate the risk of virus-contaminated feed using a model based on real-world conditions. This new model used an “ice-block” challenge, containing equal concentrations of porcine reproductive and respiratory syndrome virus (PRRSV), Seneca-virus A (SVA) and PEDV, larger populations of pigs, representative commercial facilities and environments, along with realistic volumes of complete feed supplemented with selected additives. Following supplementation, the ice block was manually dropped into designated feed bins and pigs consumed feed by natural feeding behavior. After challenge, samples were collected at the pen level (feed troughs, oral fluids) and at the animal level (clinical signs, viral infection, growth rate, and mortality) across five independent experiments involving 15 additives. In 14 of the additives tested, pigs on supplemented diets had significantly greater average daily gain (ADG), significantly lower clinical signs and infection levels, and numerically lower mortality rates compared to non-supplemented controls. In conclusion, the majority of the additives evaluated mitigated the effects of PRRSV 174, PEDV, and SVA in contaminated feed, resulting in improved health and performance.