The risk of viral transmission in feed: What do we know, what do we do?

Quantitative risk assessment of African swine fever introduction into Spain by legal import of swine products

African swine fever (ASF) is currently threatening the global swine industry. Its unstoppable global spread poses a serious risk to Spain, one of the world's leading producers. Over the past years, there has been an increased global burden of ASF not only in swine but also swine products. Unfortunately, many pigs are not diagnosed before slaughter and their products are used for human consumption. These ASF-contaminated products are only a source for new ASF outbreaks when they are consumed by domestic pigs or wild boar, which may happen either by swill feeding or landfill access. This study presents a quantitative stochastic risk assessment model for the introduction of ASF into Spain via the legal import of swine products, specifically pork and pork products. Entry assessment, exposure assessment, consequence assessment and risk estimation were carried out. The results suggest an annual probability of ASF introduction into Spain of 1.74 × 10-4, the highest risk being represented by Hungary, Portugal, and Poland. Monthly risk distribution is homogeneously distributed throughout the year. Illegal trade and pork product movement for own consumption (e.g., air and ship passenger luggage) have not been taken into account due to the lack of available, accredited data sources. This limitation may have influenced the model's outcomes and, the risk of introduction might be higher than that estimated. Nevertheless, the results presented herein would contribute to allocating resources to areas at higher risk, improving prevention and control strategies and, ultimately, would help reduce the risk of ASF introduction into Spain.

Spatiotemporal relative risk distribution of porcine reproductive and respiratory syndrome virus in the United States

Porcine reproductive and respiratory syndrome virus (PRRSV) remains widely distributed across the U.S. swine industry. Between-farm movements of animals and transportation vehicles, along with local transmission are the primary routes by which PRRSV is spread. Given the farm-to-farm proximity in high pig production areas, local transmission is an important pathway in the spread of PRRSV; however, there is limited understanding of the role local transmission plays in the dissemination of PRRSV, specifically, the distance at which there is increased risk for transmission from infected to susceptible farms. We used a spatial and spatiotemporal kernel density approach to estimate PRRSV relative risk and utilized a Bayesian spatiotemporal hierarchical model to assess the effects of environmental variables, between-farm movement data and on-farm biosecurity features on PRRSV outbreaks. The maximum spatial distance calculated through the kernel density approach was 15.3 km in 2018, 17.6 km in 2019, and 18 km in 2020. Spatiotemporal analysis revealed greater variability throughout the study period, with significant differences between the different farm types. We found that downstream farms (i.e., finisher and nursery farms) were located in areas of significant-high relative risk of PRRSV. Factors associated with PRRSV outbreaks were farms with higher number of access points to barns, higher numbers of outgoing movements of pigs, and higher number of days where temperatures were between 4°C and 10°C. Results obtained from this study may be used to guide the reinforcement of biosecurity and surveillance strategies to farms and areas within the distance threshold of PRRSV positive farms.

Survival of a surrogate African swine fever virus-like algal virus in feed matrices using a 23-day commercial United States truck transport model

African swine fever virus (ASFV) is a member of the nucleocytoplasmic large DNA viruses (NCLDVs) and is stable in a variety of environments, including animal feed ingredients as shown in previous laboratory experiments and simulations. Emiliania huxleyi virus (EhV) is another member of the NCLDVs, which has a restricted host range limited to a species of marine algae called Emiliania huxleyi. This algal NCLDV has many similar morphological and physical characteristics to ASFV thereby making it a safe surrogate, with results that are applicable to ASFV and suitable for use in real-world experiments. Here we inoculated conventional soybean meal (SBMC), organic soybean meal (SBMO), and swine complete feed (CF) matrices with EhV strain 86 (EhV-86) at a concentration of 6.6 × 107 virus g-1, and then transported these samples in the trailer of a commercial transport vehicle for 23 days across 10,183 km covering 29 states in various regions of the United States. Upon return, samples were evaluated for virus presence and viability using a previously validated viability qPCR (V-qPCR) method. Results showed that EhV-86 was detected in all matrices and no degradation in EhV-86 viability was observed after the 23-day transportation event. Additionally, sampling sensitivity (we recorded unexpected increases, as high as 49% in one matrix, when virus was recovered at the end of the sampling period) rather than virus degradation best explains the variation of virus quantity observed after the 23-day transport simulation. These results demonstrate for the first time that ASFV-like NCLDVs can retain viability in swine feed matrices during long-term transport across the continental United States.

Modeling between-farm transmission dynamics of porcine epidemic diarrhea virus: Characterizing the dominant transmission routes

The role of transportation vehicles, pig movement between farms, proximity to infected premises, and feed deliveries has not been fully considered in the dissemination dynamics of porcine epidemic diarrhea virus (PEDV). This has limited efforts for disease prevention, control and elimination restricting the development of risk-based resource allocation to the most relevant modes of PEDV dissemination. Here, we modeled nine pathways of between-farm transmission represented by a contact network of pig movements between sites, farm-to-farm proximity (local transmission), four distinct contact networks of transportation vehicles (trucks that transport pigs from farm-to-farm and farm-to-markets, as well as trucks transporting feed and staff), the volume of animal by-products in feed diets (e.g., fat and meat-and-bone-meal) to reproduce PEDV transmission dynamics. The model was calibrated in space and time with weekly PEDV outbreaks. We investigated the model performance to identify outbreak locations and the contribution of each route in the dissemination of PEDV. The model estimated that 42.7% of the infections in sow farms were related to vehicles transporting feed, 34.5% of infected nurseries were associated with vehicles transporting pigs between farms, and for both farm types, local transmission or pig movements were the next most relevant transmission routes. On the other hand, finishers were most often (31.4%) infected via local transmission, followed by the vehicles transporting feed and pigs between farms. Feed ingredients did not significantly improve model calibration metrics, sensitivity, and specificity; therefore, it was considered to have a negligible contribution in the dissemination of PEDV. The proposed modeling framework provides an evaluation of PEDV transmission dynamics, ranking the most important routes of PEDV dissemination and granting the swine industry valuable information to focus efforts and resources on the most important transmission routes.

Analysis of acidified feed components containing African swine fever virus

Mitigation of African swine fever (ASF) virus in contaminated feed materials would assist control activities. Various finely-ground pig feed ingredients (5 cereals, 4 plant proteins, 2 animal proteins, 1 oil, 1 compound) were sprayed and mixed thoroughly with a buffered formic acid formulation (0, 1 or 2% vol/vol) to produce a consistent and durable level of formate (1% or 2%) with consistent acidification of cereal ingredients to less than pH 4. No such acidification was noted in other ingredients. Selected representative feed ingredients were further mixed with infectious ASF virus (10⁶ TCID₅₀) or media alone and incubated for 0, 6, 12, 24, 48, 72 or 168 h. The residual ASF virus at each timepoint was quantified using qPCR and a cell culture based TCID₅₀ assay to determine survivability. Maize, rice bran and compound feed (with or without formate) all reduced infectious ASF virus to levels below the detection threshold of the cell culture assay (10^1.3 TCID₅₀/mL). A consistent reduction in ASF virus DNA levels was observed by qPCR assay when maize containing ASF virus was mixed with 1% or 2% buffered formic acid. This reduction in viral DNA corresponded to the acidifying pH effect measured. No such reduction in ASF virus DNA levels was noted in non-cereal ingredients containing ASF virus, in which the pH had not been lowered below pH 4 following treatment. Interestingly, residual ASF virus levels in spiked meat/bone meal were greater than control levels, suggesting a buffering effect of that feed ingredient.

Rapid and sensitive detection of African swine fever virus in pork using recombinase aided amplification combined with QDMs-based test strip

African swine fever virus (ASFV) is the pathogen of African swine fever, a highly contagious and fatal disease of wild boar and domestic pigs. The flow of ASFV through pork products is more concealed, higher risky, and more difficult to prevent and control. Presently, on-site ASFV detection methods in preclinical infected pigs and circulated pork products are lacking. Here, fluorescent test strip-based rapid ASFV detection method in pork was established combined with recombinase aided amplification (RAA) and quantum dot microspheres (QDMs). This method is specific to ASFV with no cross-reactivity to pseudorabies virus (PRV), porcine circovirus type 2 (PCV2), and porcine reproductive and respiratory syndrome virus (PRRSV). The method also showed highly sensitivity with a detection limit of 1 copy for ASFV plasmid templates containing B646L gene and 100 copies/g for DNA extracts from clinical pork samples within a short detection time of less than 25 min. Additionally, the method showed 99.17% consistency with real-time PCR in the ASFV detection of 120 clinical pork samples. Overall, the QDMs-based test strip method provides specific, sensitive, rapid, and simple detection of ASFV in pork, which may contribute to maintain the food safety of pork products, and facilitate ASFV traceability and prevention. Rapid and sensitive detection of African swine fever virus in pork by QDMs based test strip assay.

Understanding the role of feed manufacturing and delivery within a series of porcine deltacoronavirus investigations

Two feed mills and three breed-to-wean facilities were investigated after being diagnosed with porcine deltacoronavirus (PDCoV) with initial suspicion that feed manufacture and delivery processes were involved in disease transmission. Both feed mills were audited, and environmental samples collected in areas that were deemed high risk for virus contamination. All breed-to-wean facilities had PDCoV detected as would be expected, while the only positive samples for enteric coronaviruses associated with feed mills were feed delivery trucks. These results indicate that feed delivery surfaces can help spread virus during an ongoing disease outbreak and must be considered when determining the outbreak origin.

An analysis of select swine feed ingredients and pork products imported into the United States from African swine fever virus affected countries

The potential for feed ingredients to serve as a vehicle for African swine fever virus (ASFV) introduction to the United States remains a significant concern. It is therefore imperative that channels through which high-risk livestock feeds and feed ingredients are imported into the United States from ASFV-positive countries are identified and considered into the USDA's ASF National Response Framework. The purpose of this study is to demonstrate the use of a novel analytical tool to categorically quantify pork products and potential high-risk feed ingredients that have entered the United States from ASFV-positive countries over a 5-year period (2016-2020). Data for this study were obtained at the United States International Trade Commission Harmonized Tariff Schedule (HTS) website (www.hs.usitc.gov), a publicly available website that provides transaction information on specific trade commodities between the United States and its international trading partners. A total of 29 high-risk pork products or feed ingredients with the potential to be fed to pigs were analysed. High risk products and ingredients were defined as those that previous research has shown to facilitate extended viral survivability, and includes products such as soybean oilcake, distillers grains, pet food, and pork sausage casings. Data were exported into Microsoft Excel and organized into pivot tables to describe the quantity of each product by country of origin and Port of Entry (POE). The analysis focused on the 60 ASFV-positive countries as currently reported by the World Organization for Animal Health (OIE). In 2020, a total of 486,902 metric tons (MT) of these high-risk products were imported into the United States from a total of 19 of the 60 foreign countries currently listed as ASFV positive by the OIE. A majority of imported animal feed ingredients came from India in 2020 (85.8%; 392,243 MT), whereas the majority of pork products and by-products were imported from Poland (21,191 MT, 70.6%). Soybean oilcake from India entered the United States through a total of 15 ports of entry (POEs) in 2020. Of these POEs, a total of five POEs received greater than 91% of all of soy oilcake originating from India, including Baltimore, MD (37.7%); San Francisco, CA (30.1%); Seattle, WA (12.7%); New Orleans, LA (5.9%); and Detroit, MI (5.1%). When examining trends over a 5-year period, a few noteworthy findings include the dramatic rise in soybean oilcake imported from India when compared to China, and a dramatic decrease in the total volume of pork sausage casings imported from China into the United States. To support the risk management of feed imports, our novel approach focuses on seaport of highest risk and quantity of product received. Data provided in this report represent an initial listing of suspect pork products and feed ingredients entering the United States, much of which is destined for animal feed. Specific detailed examples are provided in order to demonstrate the tool's flexible interface, which can be quickly modified to zero-in on specific feed ingredients, countries, or POEs depending on what the user's question may be. To the authors' knowledge, the use of and application of such a tool has not been previously utilized to support ongoing risk mitigation efforts. Potential outlets for future use of the analytical tool will include a more user-friendly and interactive interface providing an inclusive analysis of global livestock feed ingredient sourcing.

Evidence of viral survival in representative volumes of feed and feed ingredients during long-distance commercial transport across the continental United States

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 tonne 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 United States.

Risk and Mitigation of African Swine Fever Virus in Feed

Simple Summary

African swine fever is the most significant disease threat to swine globally, and recent introductions into previously negative countries has heightened the risk for disease spread. Without an effective vaccine or treatment, the primary objective of negative countries is to prevent African swine fever virus infection in pigs. Significant quantities of feed ingredients used for swine diets are traded worldwide and may be imported from countries with African swine fever. If feed ingredients are contaminated with the virus, they can serve as potential routes for the introduction and transmission of African swine fever virus. This review provides information on the risk of African swine fever virus in feed and the mitigation strategies that may help protect the global swine population from introduction and spread through feed.

Abstract

Since the 2013 introduction of porcine epidemic diarrhea virus into the United States (U.S.), feed and feed ingredients have been recognized as potential routes for the introduction and transmission of foreign animal diseases of swine. Feed ingredients for swine diets are commodities traded worldwide, and the U.S. imports thousands of metric tons of feed ingredients each year from countries with circulating foreign animal diseases. African swine fever (ASF) is the most significant foreign animal disease threat to U.S. swine production, and the recent introduction of ASF into historically negative countries has heightened the risk for further spread. Laboratory investigations have characterized the stability of the ASF virus (ASFV) in feed ingredients subjected to transoceanic shipment conditions, ASFV transmissibility through the natural consumption of plant-based feed, and the mitigation potential of certain feed additives to inactivate ASFV in feed. This review describes the current knowledge of feed as a risk for swine viruses and the opportunities for mitigating the risk to protect U.S. pork production and the global swine population from ASF and other foreign animal diseases.

Modelling the transmission and vaccination strategy for porcine reproductive and respiratory syndrome virus

Many aspects of the porcine reproductive and respiratory syndrome virus (PRRSV) between-farm transmission dynamics have been investigated, but uncertainty remains about the significance of farm type and different transmission routes on PRRSV spread. We developed a stochastic epidemiological model calibrated on weekly PRRSV outbreaks accounting for the population dynamics in different pig production phases, breeding herds, gilt development units, nurseries and finisher farms, of three hog producer companies. Our model accounted for indirect contacts by the close distance between farms (local transmission), between-farm animal movements (pig flow) and reinfection of sow farms (re-break). The fitted model was used to examine the effectiveness of vaccination strategies and complementary interventions such as enhanced PRRSV detection and vaccination delays and forecast the spatial distribution of PRRSV outbreak. The results of our analysis indicated that for sow farms, 59% of the simulated infections were related to local transmission (e.g. airborne, feed deliveries, shared equipment) whereas 36% and 5% were related to animal movements and re-break, respectively. For nursery farms, 80% of infections were related to animal movements and 20% to local transmission; while at finisher farms, it was split between local transmission and animal movements. Assuming that the current vaccines are 1% effective in mitigating between-farm PRRSV transmission, weaned pigs vaccination would reduce the incidence of PRRSV outbreaks by 3%, indeed under any scenario vaccination alone was insufficient for completely controlling PRRSV spread. Our results also showed that intensifying PRRSV detection and/or vaccination pigs at placement increased the effectiveness of all simulated vaccination strategies. Our model reproduced the incidence and PRRSV spatial distribution; therefore, this model could also be used to map current and future farms at-risk. Finally, this model could be a useful tool for veterinarians, allowing them to identify the effect of transmission routes and different vaccination interventions to control PRRSV spread.

Inhibition of African swine fever virus in liquid and feed by medium-chain fatty acids and glycerol monolaurate

BACKGROUND

The ongoing African swine fever virus (ASFv) epidemic has had a major impact on pig production globally and biosecurity efforts to curb ASFv infectivity and transmission are a high priority. It has been recently identified that feed and feed ingredients, along with drinking water, can serve as transmission vehicles and might facilitate transboundary spread of ASFv. Thus, it is important to test the antiviral activity of regulatory compatible, antiviral feed additives that might inhibit ASFv infectivity in feed. One promising group of feed additive candidates includes medium-chain fatty acids (MCFA) and monoglyceride derivatives, which are known to disrupt the lipid membrane surrounding certain enveloped viruses and bacteria.

RESULTS

The antiviral activities of selected MCFA, namely caprylic, capric, and lauric acids, and a related monoglyceride, glycerol monolaurate (GML), to inhibit ASFv in liquid and feed conditions were investigated and suitable compounds and inclusion rates were identified that might be useful for mitigating ASFv in feed environments. Antiviral assays showed that all tested MCFA and GML inhibit ASFv. GML was more potent than MCFA because it worked at a lower concentration and inhibited ASFv due to direct virucidal activity along with one or more other antiviral mechanisms. Dose-dependent feed experiments further showed that sufficiently high GML doses can significantly reduce ASFv infectivity in feed in a linear manner in periods as short as 30 min, as determined by infectious viral titer measurements. Enzyme-linked immunosorbent assay (ELISA) experiments revealed that GML treatment also hinders antibody recognition of the membrane-associated ASFv p72 structural protein, which likely relates to protein conformational changes arising from viral membrane disruption.

CONCLUSION

Together, the findings in this study indicate that MCFA and GML inhibit ASFv in liquid conditions and that GML is also able to reduce ASFv infectivity in feed, which may help to curb disease transmission.

Quantification of soya-based feed ingredient entry from ASFV-positive countries to the United States by ocean freight shipping and associated seaports

African swine fever virus (ASFV) can survive in soya‐based products for 30 days with T ½ ranging from 9.6 to 12.9 days in soya bean meals and soya oil cake. As the United States imports soya‐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 analysed imports across air, land and sea POE of soya‐based products from 43 ASFV‐positive countries to the United States during 2018 and 2019. In 2018, 104,366 metric tons (MT) of soya‐based products, specifically conventional and organic soya bean meal, soya beans, soya oil cake and soya oil were imported from these countries into the United States 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 United States and 54.7% (40,143 MT) came from the Ukraine and 8.4% (6,182 MT) from China. Regarding POE, 80.9%–83.2% of soya‐based imports from China entered the United States at the seaports of San Francisco, CA, and Seattle, WA, while 89.4%–100% entered from the Ukraine via the seaports of New Orleans, LA, and Charlotte, NC. Analysis of five‐year trends (2015–2019) of the volume of soya 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 soya 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 United States.

“What a Waste”—Can We Improve Sustainability of Food Animal Production Systems by Recycling Food Waste Streams into Animal Feed in an Era of Health, Climate, and Economic Crises?

Food waste has been a major barrier to achieving global food security and environmental sustainability for many decades. Unfortunately, food waste has become an even bigger problem in many countries because of supply chain disruptions during the COVID-19 pandemic and African Swine Fever epidemic. Although Japan and South Korea have been leaders in recycling food waste into animal feed, countries that produce much greater amounts of food waste, such as the United States and the European Union, have lagged far behind. Concerns about the risk of transmission of bacteria, prions, parasites, and viruses have been the main obstacles limiting the recycling of food waste streams containing animal-derived tissues into animal feed and have led to government regulations restricting this practice in the U.S. and EU. However, adequate thermal processing is effective for inactivating all biological agents of concern, perhaps except for prions from infected ruminant tissues. The tremendous opportunity for nitrogen and phosphorus resource recovery along with several other environmental benefits from recycling food waste streams and rendered animal by-products into animal feed have not been fully appreciated for their substantial contribution toward solving our climate crisis. It is time to revisit our global approach to improving economic and environmental sustainability by more efficiently utilizing the abundant supply of food waste and animal tissues to a greater extent in animal feed while protecting human and animal health in food animal production systems.

The risk of viral transmission in feed: What do we know, what do we do?

The role of animal feed as a vehicle for the transport and transmission of viral diseases was first identified in 2014 during the porcine epidemic diarrhoea virus epidemic in North America. Since the identification of this novel risk factor, scientists have conducted numerous studies to understand its relevance. Over the past few years, the body of scientific evidence supporting the reality of this risk has grown substantially. In addition, numerous papers describing actions and interventions designed to mitigate this risk have been published. Therefore, the purpose of this paper is to review the literature on the risk of feed (what do we know) and the protocols developed to reduce this risk (what do we do) in an effort to develop a comprehensive document to raise awareness, facilitate learning, improve the accuracy of risk assessments and to identify knowledge gaps for future studies.

Major swine viral diseases: an Asian perspective after the African swine fever introduction

Asia is a major pig producer of the world, and at present, African swine fever virus (ASFV) continues to significantly impact the Asian pig industry. Since more than 50% of the world’s pig population is in Asia, ASFV outbreaks in Asia will affect the global pig industry. Prior to the introduction of ASF, several outbreaks of major swine viruses occurred in Asia over the last two decades, including porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV) and foot and mouth disease virus (FMDV). The rapid spreading of those viruses throughout Asia involve many factors such as the various pig production systems and supply chains ranging from back-yard to intensive industrial farms, animal movement and animal product trading within and among countries, and consumer behaviors. ASF has notoriously been known as a human-driven disease. Travelers and international trading are the major ASFV-carriers for the transboundary transmission and introduction to naïve countries. Globalization puts the entire pig industry at risk for ASF and other infectious diseases arising from Asian countries. Disease control strategies for the various pig production systems in Asia are challenging. In order to ensure future food security in the region and to prevent the deleterious consequences of ASF and other major viral disease outbreaks, disease control strategies and production systems must be improved and modernized.