Strategies to minimize the risk of pathogen spread via feed

Introduction

As African swine fever virus (ASFV) continues to spread across Southeast Asia, classical swine fever virus (CSFV) expands within Japan, and foot and mouth disease virus (FMDV) reports continue from China, there is increased concern that foreign animal disease (FAD) may enter previously naïve areas. Their continued entry would be devastating to the global swine industry, but also to those that produce feed and ingredients fed to pigs. In their May 2019 Food Outlook Report, the Food and Agriculture Organization of the United Nations reported that pig feed sales were down 10 to 50% in the Guangdong Province of China, and pig feed production in the Shandong Province was only 67% of the volume of 2018 (FAO, 2019).

Risks for Foreign Animal Disease Entry through Ingredients

There are many potential routes for FAD entry into naïve areas, with ingredients being just one. Many entities are taking steps to limit entry through more direct methods, such as regulating the importation of live animals or smuggling of pork products, but it is the responsibility of the feed industry to minimize the potential for FAD entry through a feed vehicle. For FAD entry via an ingredient to occur, there would need to be an initial contamination event, virus survival during transport, and consumption of virus at a dose that is capable of causing infectivity.

Contamination of an Ingredient

Several examples of introduction of FAD via the feed supply chain exist. Introduction of FMDV into Japan and South Korea have both been linked to feedstuffs (Sugiura et al., 2001; Park et al., 2014). The feeding of silage that was harvested from areas with wild boars infected with CSFV has led to illness in naïve pigs (Ribbens et al., 2004). Just five years ago, porcine epidemic diarrhea virus (PEDV) was rapidly spreading throughout the U.S. swine industry for the first time, causing high mortality in young piglets in 27 states. The root cause investigation for PEDV entry in the USA concluded the most likely cause was 1-ton polyethylene tote bags containing feed or ingredients from China (USDA 2015). Feeding contaminated feed has been categorized as a risk factor for ASFV transmission (EFSA, 2014; Belyanin, 2013). This report documented feed being associated with 35% of 284 reported outbreaks in Russia. Contaminated feed has been reported that 35% of the 284 ASFV outbreaks in Russia were linked to contaminated commercial feed. More recently, reports indicate that 1 to 2% of tested ingredients from modern Chinese feed mills were ASFV-positive, including corn, soybean meal, rice, wheat, and corn dried distillers grains with solubles (Dee and Niederwerder, 2019). Senecavirus A (SVA), a swine pathogen that causes similar clinical signs as FMDV, is endemic in swine production systems in the U.S. and was recently found to be spread via SVA-contaminated ingredients and feed in Brazil (Leme et al., 2019). The source of virus entry into the feedstuff is oftentimes FAD-containing feces, which may be introduced into the ingredient through cross-contamination during grain drying or ingredient transportation. Alternatively, in our team’s work with a swine production system in Vietnam, none of the 40 feed or ingredient samples collected contained detectable ASFV DNA. Notably, the feed mills in this production system were all using a formaldehyde-based additive. These contrasting cases illustrate that there are clearly differences in the prevalence and distribution of ASFV in ingredients, and many factors must be considered when evaluating ingredient contamination.

Virus Survival during Transport at Concentrations Capable of Causing Infection

Theoretical survival of FMDV (via a Senecavirus A surrogate) and ASFV has been demonstrated by Dee et al. (2018), while CSFV does appear to be as likely to survive transportation. Niederwerder et al. (2019) reported that pigs consuming ASFV-contaminated feed can become infected when consuming a single 100 g meal of feed containing a single dose of ASFV (10⁴ TCID₅₀/g) ASFV. By modelling this data, it is expected exposure of pigs to 30 meals containing a low dose of ASFV (10⁰ TCID₅₀/g) will lead to a significant probability of infection. Feed industry equipment and processes are designed to efficiently mix low inclusion products uniformly throughout a batch of feed, and then deliver feed in a method that provides multiple meals with the same consistency to many pigs housed in the same location. If ASFV or another FAD enters the feed supply chain and is mixed into a batch of feed, the results could be catastrophic contamination across multiple herds. For example, Schumacher et al. (2016) reported that if 1 g of feces from an acutely infected pig with porcine epidemic diarrhea virus (PEDV) entered a receiving pit, it could potentially contaminate 500 metric tons of feed, with each gram having a dose capable of causing infectivity. That is the equivalent of twenty 24-ton feed trucks, all carrying infectious material to different facilities. Simultaneously, the entry causes contamination of the feed manufacturing equipment. In 2017, Schumacher et al. reported that entry of PEDV into a feed mill leads to nearly 100% of surfaces being contaminated, including non-contact surfaces such as walls and floors. Finally, Huss et al. (2017) reported that the cleaning and disinfection necessary to sanitize a virus-contaminated feed mill includes complete organic material removal, followed by wet-cleaning with a glutaraldehyde and later bleach sanitizer. The feed industry is not designed for this type of cleaning and disinfection, so the primary focus must be on keeping pathogenic viruses out of feed mills. This includes a focus on both the source of the ingredients, but also their transportation. The incubation period for ASFV is 5 to 21 days and it may be up to 3 weeks after an animal is exposed before signs of the disease occur. During this time, the feed supply chain may be unknowingly transmitting virus. Therefore, strenuous actions are necessary to prevent feed mills from being a source of cross-contamination.

Recommendations for Swine Feed Manufacturers to Minimize the Potential for ASFV and other FAD Entry and Transmission via the Feed Supply Chain:

1.Know your supplier. It is key that facilities can identify the supplier of the ingredients coming into their facility. This process helps maintain transparency across the feed supply chain. In some facilities, procurement is independent from quality control and feed safety. These need to be fully integrated, with a system for checks and balances to ensure that the most economical ingredients are used, but only if they are not a potential risk for disease entry. Knowledge of the ingredients supply chain should extend from the point of ingredient manufacture through transportation to the feed mill, including any intermediaries or blending locations.

2. Do not use grains or oilseeds (or their resultant meals) from regions with foreign animal disease. Feed mills manufacturing feed for multiple species should follow this for the entire mill, not just exclude it from swine feed. For example, it has been reported that mills manufacturing feed for sow multiplication facilities are also manufacturing organic dairy feed, with imported organic soybean meal from China being used only in dairy feed. Because of the potential for batch-to-batch and environmental contamination, these high-risk ingredients should be excluded from the mill altogether.

3. If using other ingredients from regions with foreign animal disease, take steps to ensure they are at low risk for disease transmission.The Decision Tree Matrix to Minimize Viral Transmission Risk from Feed Ingredients produced by the Swine Health Information Center and other leading swine organizations can aid in this assessment. In particular, consider both the point of manufacture and its method of transportation. It may be appropriate to have different procedures for receipt of ingredients transported in different forms. For example:

a. If ingredients are delivered in bulk (vessel, barge, rail, or truck), require washout tickets or proof of low-risk loads since the previous washout prior to receipt.

b. If ingredients are delivered in bulk tote bag, obtain proof that bags were not reused prior to loading and inspect the bags for damage prior to receipt.

c. If ingredients transported in small, single-use, sealed bags, sanitize the pallet, pallet jack, trailer floor, and any plastic wrapping prior to receipt. Inspect bags for damage prior to receipt and the use of disallow wooden pallets.

4. Use porcine-based ingredients with caution. Porcine-based ingredient production is likely to contain a killstep capable of destroying viruses. However, post-processing cross-contamination may exist, causing the potential for these ingredients to be sources of viral entry into mills. If porcine-based ingredients are used, obtain these ingredients from suppliers with documented biosecurity procedures and programs to reduce the risk of post-processing cross-contamination. If there is concern about ASFV or CSFV, other animal protein ingredients can be used with negligible risk. If the concern extends to FMDV, ensure that all suppliers of animal proteins have adequate programs to address biosecurity and post-processing contamination.

5.Implement biosecurity at the mill. Biosecurity procedures have been in place for decades on swine farms to limit disease transmission by people and delivery vehicles. These same principles should be extended to mills.

a. Develop a feed mill biosecurity plan. Methods for developing a swine feed mill biosecurity plan are described by Cochrane et al., 2016. Other references, such as the AFIA guide for Developing Biosecurity Practices for Feed & Ingredient Manufacturing, and the K-State Swine Feed Mill Biosecurity Audit are helpful for facilities to determine opportunities for improving biosecurity.

b. Use receiving mats or funnels to limit pathogen entry into the receiving pit. The ingredient receiving pit is the single biggest entry point for contaminants into the feed manufacturing system. Magossi et al., 2019 reported that the pit was second to only employee shoes as the most unhygienic locations tested in 12 U.S. feed mills.

c. Create lines of separation at all doors to minimize contamination from footwear. This involves employees and visitors changing shoes to keep exterior shoes on one side of the line and interior shoes on the other. Examples of how facilities may implement lines of separation are shown in Figures 1 and 2. In both examples, additional exits are available in case of emergency to satisfy OSHA requirements. If lines of separation cannot be developed, consider zoning to standardize traffic patterns, with foot baths or food-grade dry sanitizing powder placed in high traffic areas.

Figure 1. Feed mill entry with a bench delineating areas between outside footwear and that worn inside the mill area.

Figure 2. Feed mill entry from the receiving bay delineating areas between outside footwear and that worn inside the mill area.

d. Create cleaning and disinfection stations for delivery vehicles and feed trucks. Use wet-cleaning and sanitizers to remove debris from the tires, wheels, undercarriage, and exterior of ingredient trucks and feed delivery trucks prior to their entry into the mill. This is particularly pressing in times when disease pressure is high. Be sure that all vehicles are rinsed or dried prior to entry into the mill to prevent cleaners or sanitizers from being a source of contamination themselves.

e. Sanitize floors routinely. Sweep or vacuum all dirt and dust from floor, then mop on a weekly basis to limit the accumulation and spread of virus on non-feed-contact surfaces. Mopping material should be a bleach solution with at least 2.3% chlorine or an EPA-approved FAD disinfectant, such as a solution with at least 1% Virkon™ S.

f. Refrain from using dust, screenings, or similar materials as an ingredient or added back into feed production. These materials are frequently placed back in ground corn or an ingredient bin to minimize shrink. However, dust is consistently reported to carry high levels of pathogens, and should be composted or discarded, never fed to animals.

6. When delivering feed, use cleaning and disinfection stations prior to entering and exiting farms. Alternatively, consider unloading feed across a line of segregation or fence into another feed truck or extend bin augers so bins can be filled on the exterior of the line of segregation, as shown in Figure 3.

Figure 3. Barn with bins located outside the fenced perimeter so that feed delivery trucks are not required to cross a line of separation to deliver feed.

Barn with bins located outside the fenced perimeter so that feed delivery trucks are not required to cross a line of separation to deliver feed.

In our study with the Vietnam production system, a total of 724 environmental samples were collected from the feed manufacturing and delivery process, with 1.1% containing ASFV DNA. One of these positive samples came from a feed mill, with the remainder occurring from feed delivery truck cabs. The positive feed mill sample was from a floor surface where feed delivery truck drivers wear footwear that had been previously exposed to surfaces outside the feed mill. This demonstrates that feed delivery continues to be a weak point in biosecurity protocols, and that footwear must be considered when optimizing feed mill biosecurity.

Conclusions

We are in a new era of feed production, where feed safety is just as paramount as quality and tonnage. Unfortunately, some mills struggle to implement changes that maximize feed safety because it is difficult to establish a Return on Investment calculation for the extra effort. Still, the cost of foreign animal disease entry into a mill would be catastrophic, and therefore we must adapt our culture to make feed that is not just wholesome, but also safe.

Published in the proceedings of the International Pig Veterinary Society Congress – IPVS2020. For information on the event, past and future editions, check out https://ipvs2022.com/en.

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Strategies to minimize the risk of pathogen spread via feed

References

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