Introduction
What is biosecurity? Biosecurity can be subdivided into 3 parts: 1) bio-exclusion involves keeping pathogens out of a herd, 2) bio-management involves managing pathogens already in a herd to minimize the negative consequences, and 3) bio-containment involves preventing pathogens from escaping a herd and putting other farms at risk. Bio-exclusion will be the focus of this factsheet.
Improving bio-exclusion requires taking time to identify the most significant vulnerabilities on farms to determine what should be done next. It starts with identifying vulnerabilities that can result in pathogens being introduced into a herd (step 1) and then prioritizing bio-exclusion control measures to address them (step 2). Historically, relatively little time has been spent on the first step resulting in slow progress in improving biosecurity.
Objectives
This factsheet will cover how to:
- Identify vulnerabilities that can result in pathogens being introduced into a herd
- Implement bio-exclusion control measures to address the vulnerabilities
Identifying vulnerabilities
Introduction of pathogens into herds
Pathogen carrying agents and entry events. Because viruses are not capable of locomotion, they must be carried by something else. The term “pathogen carrying agent” describes any object, animal, or person that may carry a virus into the breeding herd (Zimmerman et al., 2019). A pathogen carrying agent may directly transmit the pathogen by being infected or indirectly by being contaminated with the pathogen. The entry of pathogen carrying agents, delineated by when they cross the outer perimeter of the farm, can be characterized as carrying agent entry events. A “carrying agent entry event” is defined as one or more potential pathogen carrying agents crossing the outer perimeter, physical or abstract, of the swine farm.
An example of a pathogen carrying agent entry event is depicted in Figure 1. When breeding replacements are delivered to the farm, there is typically multiple pathogen carrying agents associated with the event, including the animals, livestock trailer, truck, driver and their equipment. The event occurs when the carrying agents associated with that event cross the outer perimeter of the farm. Carrying agent entry events that typically occur on sow farms are summarized in Figure 1. Some carrying agent entry events, such as entry of air and water, occur continuously. For discrete events that are easily observed and recorded, such as entry of semen and removal of manure, a date(s) or frequency over some period of time can be determined. For others that are discrete but not always observed, such as entry of rodents and other wild animals, a subjective assessment of how frequently or intensively they occur can be made.
Assessing hazards and failures. In the context of identifying vulnerabilities, a hazard is any circumstance or action (or inaction) that is reasonably likely to result in a failure that may lead to the introduction of a pathogen into a herd. The hazards lay in the who, what, when, where and how production and production-related processes associated with the events in Figure 2 are performed. To identify the hazards, the steps involved with each carrying agent entry event and opportunities for failure should be understood and documented. A series of 3 failures is required for a pathogen to be introduced into a herd by a pathogen carrying agent (Figure 3) (Zimmerman et al., 2019).
Figure 1: Example of a pathogen carrying agent entry event; delivery of breeding replacements.
Figure 2: Carrying agent entry events that typically occur on sow farms.
Figure 3: Series of three failures is required for a pathogen to be introduced into a herd by a pathogen carrying agent.
Bio-exclusion control measures
Control measures include any change in the process that can be used to prevent, eliminate or reduce a significant hazard. Biosecurity practices that show up on lists do not typically address all of the potential hazards. Bio-exclusion control measures can involve simple changes to the production processes. For example, moving the location where semen is delivered by the boar stud and picked up by on-farm employees from a site with a large amount of swine transport activity (e.g., a scale) to a site with no swine transport activity may be an effective control measure. It eliminates a hazard and reduces the probability of the employees or semen packaging from being contaminated (Failure 1).
Hierarchy of risk reduction
Not all bio-exclusion control measures are equal. The best control measures are those that eliminate a hazard or substitute small hazards for large hazards. Switching from rendering to on-site disposal of dead animals is an example of substituting the hazards associated with rendering pickup with the much smaller hazards associated with dead removal. The next best control measures are engineering controls that do not involve people to be implemented. An example of an engineering control would be the installation of locks on doors controlled by a timer or keypad with automatic locking. The least effective are biosecurity control measures that involve people. When people are involved, compliance and quality of compliance must be carefully cultivated with written protocols, signage, training, audits, and other devices. In practice, most of the bio-exclusion control measures implemented on swine farms involve people in some way. There are very few purely engineering controls.
The Swiss Cheese model
The concept of layering bio-exclusion measures to address hazards is sometimes referred to as the Swiss Cheese model. Consider an employee that arrives at a farm with a pathogen contaminant on their shoes. Individual control measures, such as a shower-in, would help mitigate the contamination, but it is not full-proof, just as a single slice of Swiss Cheese has holes. A bench entry for the removal of shoes is another control measure that is not entirely effective. However, if a bench entry and shower are both required (i.e., layered), the likelihood of failing to mitigate the contamination on the employee’s shoe or prevent it from being transmitted to the pigs in the herd is lower, just as putting multiple slices of Swiss Cheese creates a block of cheese with few holes. Layering results in more robust bio-exclusion that can deal with mistakes.
Checklist of hazards and control measures
A checklist of potential hazards and bio-exclusion control measures for the major pathogen carrying agent entry events (swine movements, deliveries and removals, and people movements) in Figure 2 are included in Table 1. The list of hazards and control measures is not comprehensive.
Table 1: Checklist of potential hazards and bio-exclusion control measures for the major categories of pathogen carrying agent entry events (not a comprehensive list).
Summary
Improving bio-exclusion requires assessing hazards to identify the most significant vulnerabilities on farms. Assessing the hazards can aid in the prioritization of necessary improvements in bio-exclusion. Taking the time to assess the hazards will result in more efficient use of resources and reduce the frequency of outbreaks. Most of the bio-exclusion measures that are practical involve people, and people make mistakes. Layering of multiple bio-exclusion measures is more resistant to mistakes and, therefore, more robust.
References and Citations
Zimmerman, J. J., Dee, S., Holtkamp, D. J., Murtaugh, M., Stadejek T., Stevenson, G. W., Torremorell, M., Yang, H., Zhang, J. (2019). Porcine reproductive and respiratory syndrome viruses (porcine arteriviruses). In: Diseases of Swine, 11th edition. Zimmerman J.J, Karriker L.A., Ramirez A., Schwartz K.J., Stevenson G.W (eds.). John Wiley and Sons, Inc, Hoboken New Jersey. pp. 685-708.
