Viral Transmission Through Feed

Introduction

On August 28, 2021, the United States Department of Agriculture (USDA) confirmed that African swine fever virus (ASFV) had been diagnosed in the Dominican Republic (https://www.aphis.usda.gov/aphis/newsroom/news/sa_by_date/sa-2021/asf-confirm). This poses a tremendous threat to the swine industry of the United States (U.S.) given the proximity to the mainland. When ASFV emerged in China, the virus was able to move rapidly and easily throughout the country due to movement of animals and contaminated fomites, showcasing the ability of ASFV to cause disastrous consequences on a naïve pig population. An introduction of ASFV into North America is a serious threat because of significant trade relationships with countries that have endemic ASFV. Regulatory control of live animals and pork-containing foods substantially reduces this risk, but there is evidence that feed and/or ingredients may be potential vectors of ASFV introduction.

Previous research has been conducted to determine the minimum infectious dose of ASFV in water and feed (Niederwerder et al. 2019). The authors concluded that ASFV can be easily transmitted orally through natural consumption of both liquid and feed. Recent research has also demonstrated that ASFV can survive in various feed ingredients during transboundary, transatlantic shipping (Dee et al., 2018). Because ASFV can survive in feed during shipping, the US is rightfully concerned that a contaminated feed or ingredient will introduce ASFV into the US swine population. Regardless of its method of entry, there is concern that infection of US pigs may result in contamination of the feed supply chain, and rapid and widespread distribution of the virus like what was seen with PEDV. Therefore, the purpose of this paper will be to briefly review the risk of feed as a vector for ASFV and key feed mill biosecurity practices to reduce the risk of spreading ASFV via the feed.

Distribution of African Swine Fever Virus Into the Feed Manufacturing Environment

Regardless of potential ASFV method of entry into North America, there is valid concern that once in North America there will be rapid and widespread distribution of the virus like what was observed with PEDV (Schumacher et al., 2017). There are multiple known ASFV transmission routes that have been previously described including direct pig to pig contact, consumption of contaminated food products (swill feeding), or other fomites such as vehicles, workers, or other equipment. (Bellini et al., 2016; Guinat et al., 2016; Olesen et al., 2020). Recent surveillance research conducted in Vietnam by Kansas State University and collaborators investigated the epidemiology of ASFV transmission, particularly focusing on the movement of ASFV through the supply of swine feed and transportation. Our goal was to understand the potential areas within a swine production, feed manufacturing, and distribution system where detection of ASFV DNA could be found. It was discovered that a common source of ASFV DNA detection was in the truck cabs (Gebhardt et al., 2021). Identifying this gap led the production system to alter their biosecurity practices and incorporate truck cab decontamination procedures and restrictions on employee traffic associated with feed delivery. These changes led to major improvements in biosecurity. Although these biosecurity practices are important to consider for reducing the spread of ASFV, they would also be beneficial to reduce the spread of current endemic diseases. It has also been demonstrated that truck foot pedals can be a common area with contamination of PEDV or porcine delta coronavirus (Greiner, 2016).

For biosecurity purposes, it is important to reduce the risk of bringing a virus from the farm back to the feed mill. Elijah et al. (2021) investigated the risk of ASFV mill and subsequent batches of feed contamination when using ASFV contaminated ingredients in the feed manufacturing process. The authors determined that the distribution of ASFV into the feed manufacturing environment is widespread and persists even after manufacturing additional feed batches initially free of ASFV (Table 1). It was also demonstrated that transient surfaces play an important role in the spread of the virus through the feed mill. This is similar to what is observed with PEDV (Schumacher et al., 2017) and indicates that it is extremely important to prevent the entry of ASFV or other endemic viruses into feed mills. Once these viruses enter a feed mill, they have the potential to remain in the environment for an extended period of time. This information becomes vary pertinent because feed manufacturing facilities are not designed to easily be cleaned and disinfected. If a feed manufacturing facility becomes contaminated with a virus, there are no current recommendations for best practices to clean and disinfect these facilities. Research is being conducted to determine optimal methods for disinfecting feed manufacturing facilities, especially equipment that is not designed to be disinfected. Therefore, moving objects like people, PPE, and trucks should be taken in account when designing feed biosecurity protocols and feed/feed mill surveillance could be pivotal in maintaining appropriate feed biosecurity.

Table 1. Main effect of feed batch and zone on detection of African swine fever virus (ASFV) during manufacture of virus inoculated feed (Elijah et al., 2021)

Strategies to Reduce Risk of Viral Transmission Through Feed

Keeping feed mills clean from contamination of viruses, such as PEDV and ASFV, is important to reduce the risk of disease spread. Multiple factors must be considered to determine what steps need to be considered or implemented to the reduce the risk of virus contamination. Traditionally, feed mills were not designed with biosecurity in mind and not all feed mills are designed the same. Therefore, acceptable degree of risk and the practical implication of biosecurity practices must be considered on a case-by-case basis. Below are key actions to consider to reduce the risk contaminating feed mills.

Ingredient Sourcing

Ingredient sourcing is an important step to prevent biological hazards from entering the feed manufacturing facility via ingredients. Ingredients from areas experiencing disease outbreaks have a greater potential for being high-risk. To accurately identify ingredient risk, knowledge of the ingredient supply chain should extend from the point of ingredient manufacture through transportation to the feed mill, including any intermediaries or blending locations. Supplier identification is important to maintain transparency across the feed supply chain. It is also important to identify biosecurity practices that may be implemented throughout this supply chain. Some of these practices include heat treating the ingredients or feed or holding the ingredient outside of the mill long enough that the virus or bacteria becomes inactive. Regardless of where an ingredient is being sourced from, each step of the shipping and transportation process from manufacturing to the feed mill should be tracked. Identified biological hazards will depend on the species in which feed is being manufactured. However, the entire feed mill needs to be considered as opposed to species specific diets. To prevent mill contamination via ingredients, a balance required for quality, feed safety, and procurement areas of the mill to all work together on ingredient sourcing.

Receiving and Loadout Practices

Risk of ingredients previously discussed the movement of trucks and people through receiving poses a significant risk in terms of biosecurity. In terms of biosecurity, the main goal of feed mill should be to prevent contaminated material for entering the receiving pig. Ensuring the underside of the truck is clean before entering the receiving bay also helps reduce the chance of debris entering the pit. Instituting a tire and undercarriage wash prior to trucks entering the mill will help to minimize the chance of contaminants being brought into the receiving bay. In addition, using pit covers while trucks are entering and leaving the receiving bay helps to prevent any debris from falling into the pit and contaminating ingredients. Sweeping spilled ingredients into the pit is another thing to be avoided. Due to the nature of trucks entering and leaving, the ground in the receiving area can not be considered "clean" or safe for biosecurity and sweeping spilled ingredients into the pit is a risk of introducing disease into the mill.

In addition to the vehicles themselves, truck drivers pose another entry point of contamination. Drivers delivering ingredients or picking up finished feed should not enter the mill beyond the receiving bay to prevent tracking potential contaminants to other areas. Implementing a degree of separation between feed delivery drivers and employees in the mill also prevents contamination from trucks that have been on farms from entering the rest of the mill. Having drivers receive paperwork through a window or from the other side of a door at the office can create this separation. Also having drivers observe potential biosecurity risks at the farms they deliver to can help determine better delivery route options. Farms where exhaust fans are directed toward the feed bins or carcass disposal is near the driveway may need to receive feed later in the day to reduce the chance of bringing disease back to the mill. Having a biosecurity kit in feed delivery trucks helps reduce the risk of contamination. This kit should contain disposable plastic booties for whenever the driver needs to exit their truck, disinfectant to wipe or spray down their cabs, and a method to dispose of these items. In winter months, multiple sets of rubber overshoes could be used instead of the plastic booties, but each pair would need to be disinfected after use.

Zones in the Mill

Feed mill managers should focus on ways to separate the mill into specific zones and limit employee crossover between zones. This helps prevent employees from carrying contaminants from their shoes or clothing through the mill. For instance, an employee may help in receiving and carry contaminated feed dust on their clothes as they walk through the mill to change a die in pelleting. That contamination is no longer limited to the receiving area and now can come in contact with finished feed. Having one zone designated for receiving, another for mixing and processing, and another at load-out helps to prevent this sort of cross-over by preventing employees from moving between areas without going through a decontamination process. This zoning of the mill also needs to cover tools and equipment that might be shared between areas. To have this process be effective, each zone needs its own sets of tools, brooms, ladders, etc. to prevent these items from carrying contamination through the mill as well.

Feed Handling

Preventing finished feed from contacting surfaces that also handle raw ingredients adds another layer of feed security. Disease mitigation measures like heat treatment (pelleting or extrusion) are effective at killing or inactivating bacteria and viruses in the feed but do not prevent recontamination. As a result, sharing equipment between finished feed and raw ingredients should be avoided. When complete separation is not possible, equipment should be thoroughly disinfected before finished feed is run through it. Dust and screenings are also known to contain higher levels of pathogens than the bulk of the ingredient load. These residues should be discarded instead of being added back to ingredients or feed to prevent the accumulation of pathogens.

Employee Training

Employees need to receive proper training for any biosecurity plan to succeed. Ensuring that they are aware of the mill's biosecurity plan, FSMA regulations, and pathogen mitigation and prevention strategies helps to encourage compliance. Proper disinfecting procedures should not be overlooked. Many disinfectants require a certain amount of time in contact with a surface in order to kill pathogens. The presence of dust, grain, or other materials can also limit the effectiveness of disinfectants. All of this should be communicated to employees and biosecurity refreshers should be implemented at intervals throughout the year to keep the plan up-to-date and fresh in employee’s minds.

Culture

The most important aspect of a mill biosecurity plan is the culture of the workplace. A strong employee culture encourages everyone to implement the procedures and follow them. If management does not take their policies seriously, there is little incentive for the rest of the employees to follow the policies as well. Encouraging employees to follow a biosecurity protocol starts with management and is strengthened with knowledge of why the plan matters.

Conclusion

In conclusion, data has demonstrated the ability of viruses, such as PEDV and ASFV, can be distributed throughout the feed supply chain. It has also been confirmed that the distribution of ASFV into the feed manufacturing environment is widespread and persists even after manufacturing additional feed batches initially free of ASFV. This is similar to what is observed with PEDV and indicates that it is extremely important to prevent the entry of ASFV into feed mills. Therefore, reducing the risk of ASFV or other biological hazards in feed manufacturing facilities is an important part of the complete biosecurity plan for pig producers.

Presented at the 2022 Animal Nutrition Conference of Canada. For information on the next edition, click here.