Biosecurity efforts cost considerable resources, both human and financial, and must be predicated on economic considerations. However, when we consider the risk of zoonotic agents, those that can affect humans, economics may become a secondary factor.
In fact, it is estimated that 75% of all infectious diseases of humans come from animals. Most of these originate from wildlife like rabies, West Nile virus and Human Immunodeficiency Virus (HIV). But domestic livestock are not excluded. Pigs continue to harbor a few occasional zoonotic agents, but the industry has done a stellar job of reducing zoonotic risk.
Even so, E. coli, methicillin-resistant Staphylococcus aureus (MRSA), salmonella, yersinia, erysipelas, leptospirosis, hepatitis E and swine influenza virus, along with a few other infectious agents, remain as potentially important diseases that can infect people.
However, farm workers do not appear to be at a greater risk of developing disease from these agents than the general public.
Many of the critics of modern animal agriculture also consider antibiotic resistance as a form of zoonosis, potentially afflicting harm on humankind. The scope of antimicrobial resistance is too large to be considered in this general biosecurity discussion.
Seasonal influenza (human), salmonella and E. coli bacteria are a few of the agents that can transmit from humans to pigs.
Biosecurity should address both sides of the transmission issues.
The modern pig farm is typically operated all-in, all-out by room, by barn, and in large operations, by site. Biosecurity has become an important component of this production structure and greatly reduces disease risk or its expression.
This modern model is used by the vast majority of our industry, regardless of operation size. It reduces stress, movement and mixing, and allows more efficient and efficacious use of vaccines and antibiotics. It also reduces the risk of disease agents moving from pig-to-pig, pig-to-human and vice versa. The modern North American pig production system is a sustainable and efficient modus operandi, especially auspicious at reducing zoonosis potential by comparison to other pig industries around the world.
Those efforts have successfully eliminated or nearly eliminated lice, mange, roundworms, kidney worms, hook worms, degenerative atrophic rhinitis, pseudorabies, Classical Swine Fever (hog cholera), Actinobacillus pleuropneumonia (APP), eperythrozoonosis (Mycoplasma suis), trichinosis, tuberculosis, nodular worms, thorny-headed worms, swine pox, Transmissible gastroenteritis (TGE), vesicular stomatitis, swine brucellosis and a host of other disease agents from our swine industry. It was not so many years ago that these plagued pork production.
Only two of these agents were disposed of through government-sponsored-and-financed programs — hog cholera and pseudorabies. The others were eliminated or controlled by committed producers, high-health genetic suppliers, dedicated veterinarians and by modern all-in, all-out production methods.
Although antibiotics and vaccines have been useful, they alone didn't contribute to this massive shift in swine health. Concentrated animal feeding and breeding operations (CAFOs), which keep our pigs safe from disease while protecting the public health by avoiding zoonotic agent introductions, are the centerpiece of modern pig production, care and animal well-being.
This is the truth about CAFOs and the industrialized model. Even our smallest producers have adopted some or all of these practices. Although not perfect, our confinement operations provide the greatest efficiency, protection to the pigs and the farm workers; offer the greatest protection to public health; and are the most sustainable, efficient and disease-free operations in the global marketplace.
Biosecurity procedures are designed to keep new diseases out; control those already present by limiting transmission and infection; and, if needed, contain any new disease agent, thereby preventing its spread to other farms or production segments.
Biosecurity can be divided into bioexclusion, biomanagement and biocontainment. Bioexclusion is often referred to as external biosecurity, bio-management as internal biosecurity.
Often, a new agent enters a segment of production (i.e. boar stud) but is transmitted to other sites because functional (effective) biosecurity methods are lacking. In this situation, functional monitoring is an essential component of biosecurity.
Internal biosecurity includes those methods that reduce the impact of disease agents already present in the operation. This is accomplished by reducing the dose of the agent, increasing herd immunity to the agent, controlling the timing of infection, and reducing environmental and biological stress. Both components of biosecurity will be discussed as they pertain to pig-to-pig, people-to-pig and pig-to-people risk factors.
There are numerous internal and external biosecurity procedures employed by the pig industry. Many are traditional and based on good common sense or extrapolated from human health or other industries. Over 20 years, much research emphasis has been applied to the swine industry, greatly improving our understanding of “functional biosecurity” — that which provides true cost-effective protection.
In all cases, the expected value created by exclusion and control over disease agents should be calculated and compared to the expected, continuous cost of the interventions. When global foreign animal diseases (FADs) are considered, almost any intervention of merit will meet this value criterion when considering the macroeconomic effect.
Next Page: Biosecurity Goals
Biosecurity goals should be established as the first step of any biosecurity plan. For example, if the expectation is to keep out the porcine reproductive and respiratory syndrome (PRRS) virus, then we must understand the risk factors involved, rank them in order of importance and estimate the cost to apply functional interventions at each critical control point.
Farm biosecurity strategies should be developed utilizing a Hazard Analysis Critical Control Point (HACCP) approach. Knowledge from scientifically applied field trial methodology, risk assessment, peer-reviewed publications and significant field experience should be heavily relied upon when establishing the critical control points.
Extensive interviews and inputs from all farm staff should be included in the early stages of the hazard analysis assessment. Without participation of the farm employees, many critical control points (CCP) will be overlooked. Once the CCPs are identified, only then can intervention strategies be developed. Only those evidence-based intervention strategies that have demonstrable usefulness in the field are applicable.
A hierarchy of interventions based on relative risk assessment can then be developed — in the end, focusing on those factors that have greatest impact and opportunity for success. Here is a helpful formula for determining appropriate implementation decisions:
Functional Biosecurity Interven-tion Value (BIV) = DEV × RR/DD - IC
Where:
DEV = Disease Exclusion Value per pig (sow, etc.) per year
RR = percent Risk Reduction per year for any intervention (From the PRRS Risk Assessment Tool, etc.)
DD = Degree of Difficulty (Ranking 1-10 with 10 = very difficult/maintain)
IC = Intervention Cost per pig (sow, etc.) per year
Using this formula, each agent and each intervention strategy can be analyzed. These computations can then be used for choosing those strategies that have a final BIV greater than zero.
Although arbitrary, the DD allows us to consider a customized score for the complexity of an intervention and the ability of the farm staff to adopt, implement and sustain an intervention procedure or process. It becomes farm- or system-specific, which is ideal in the real world. If several diseases have similar risk reduction for the same intervention, then the DEVs can be added together and the sum entered into the equation. As multiple agents are considered, the strength of the intervention strategy becomes apparent.
Of course, we don't know all the risk factors, values of disease exclusion, or the percent RR, but from the risk assessment tool, published information and biosecurity experts, one can arrive at reasonable approximations.
Developing a value equation for each disease is often a matter of benchmarking diseased pigs with those that are disease free in the same system. Some average disease cost numbers are published and also provide useful benchmarks.
PRRS is a good example. Boar stud filtration has reduced the risk of airborne introductions by more than 95%. The amount of RR for each biosecurity intervention and the perceived value for exclusion helps us arrive at a logical expectation for those interventions.
With this approach, only those interventions that have a value greater than zero are applied. The formula can easily be expanded to multiple disease agents or applied to internal biosecurity measures.
Calculating IC can be difficult and often relies on farm or industry experience. The cost of building a shower facility is relatively straightforward, but the variable costs associated with implementing showers for all who enter the farm are highly variable.
Clothing costs, frequency of replacement, increased water use, shampoo, soap, washing machine, clothes dryer, added electrical usage, employee lost work time, morale, employee retention and many other details should be objectively calculated.
Comparing this to a boot and outerwear exchange facility (Danish entry) is worth calculating. Downtime rules often create significant costs, but have very limited exclusion value.
Determining IC for downtime rules is difficult, but no more so than the calculation of its DEV. Establishing universal DEV and IC for each economically important disease agent is worthy of considerable research. Calculating the value of barn filtration may also be a daunting task, but RR must be near 100% with current filtration application and maintenance costs.
Use of the American Association of Swine Veterinarian's (AASV) PRRS Risk Assessment Tool is the ideal method for developing relative risk or percent risk reduction as each critical control point is addressed.
The value per pig for each disease agent excluded must be calculated before any logical biosecurity intervention or plan can be introduced. These calculations should consider more than the published disease cost, since this is only an industry average.
For example, for a commercial boar stud, when arriving at an exclusion value per dose of semen, multiple cost factors should be considered and entered into the formula. A list of these potential cost factors associated with a specific disease introduction may include the cost of virus dissemination to customers, increase in liability insurance, cost of a depopulation, loss of customer confidence, loss of customer base, cost of genetic replacement, loss of employees, employee retraining cost, and likely several other per-dose costs from a single introduction.
Next Page: Other Risk Factors
Without an accurate individual farm cost associated with a disease break, it is difficult to apply a value per boar or per dose for exclusion of that particular agent. Likewise, when a certain intervention prevents the introduction of more than one disease agent, then the individual value will underestimate the true value of a specific intervention.
General External Biosecurity
As discussed, external biosecurity is designed to prevent a new disease introduction to the farm. Many times individual agents require specific interventions, but often a single intervention will control or prevent entry of multiple diseases.
Before designing exclusionary biosecurity strategies, the “ecology” (complete life cycle) of a specific agent must be reasonably understood. Unfortunately, most times, we don't have full knowledge of these life cycles, which is the case with the PRRS virus.
If a farm doesn't have security against sabotage or other crimes, then functional biosecurity is lacking. Leaving the door open to unwanted intruders leaves the farm open to new disease introduction.
New disease introduction always leads to significant reductions in productivity. New agents, even when they express little or no clinical effects, add cost. When new “economically important” biological agent introductions occur, catastrophic harm can result.
Global diseases like hog cholera, foot-and-mouth disease (FMD) virus or other agents would do untold economic harm if introduced.
The introduction of the European porcine circovirus (PCV2b) during 2005 is a good example of the devastation a genetic variant of an existing disease agent can wreak. Vigilance and functional biosecurity (bioexclusion and biocontainment) are our only defense if or when one of these viruses is introduced.
There are a number of primary risk factors and sources for new swine disease agents, domestic and foreign. The most efficient method for a new introduction is through arrival with replacement females, boars or semen. Any animal that originates from another premise is a significant risk to the existing population.
Breeding stock companies and boar studs have done an excellent job of eliminating PRRS and many other economically important agents from their herds. This has considerably changed the risk equation over the last 10 years, allowing the swine industry to focus on other factors associated with direct and indirect contact with pigs/pig products, waste, airborne routes and fomites.
Isolation facilities and a logical and efficient method of monitoring new herd additions are essential for a functional bioexclusion effort. Without monitoring and a separate isolation facility, there is no protection against new diseases as long as a farm is adding new genetic stock from off-site multiplication.
Reliable testing procedures are especially important. Any pig farm that expects to keep agents out must rely on a battery of tests that are systematically and strategically applied. These protocols should be designed to detect active virus and historical exposure. Use of cotton ropes as a means to collect saliva has significantly reduced the cost and moved testing closer to a “real time” procedure.
Pig transportation (live haul) methods are the next most likely source of a new agent introduction. Again, most breeding stock companies have taken a leadership role in reducing this risk when delivering their stock. Even so, the trailers used are often difficult to clean, sanitize and disinfect.
Many disinfectants are effective against PRRS virus, TGE virus, Mycoplasmal pneumonia, salmonella, E.coli and others. But the many hiding places on most livestock trailers provide opportunity for viral and bacterial exposure to the next haul of pigs.
In recent years, trailer manufacturers have made significant efforts to reduce this risk by building trailers with very few hiding places. Still, the trailer must be responsibly cleaned, disinfected and dried or heated between loads. This is especially important when hauling cull sows and boars, breeding stock deliveries and weaned pigs where the trailer visits multiple farms in the course of a week.
Drying and heat are recent additions to the ongoing defense against disease introduction by transportation — but these methods do not destroy all potential agents. Although disinfectants are very effective when they arrive at the proper concentration, temperature and exposure time, hiding places and freezing conditions often prevent pathogen destruction.
Potbelly trailers are especially difficult to sanitize. Heat delivered to the whole trailer reaching at least 160° for 10 minutes or more is effective against many pathogens including PRRS, TGE, salmonella and E. coli. FMD virus, a global agent of dread, will not be eliminated from our vehicles by drying or current heating levels; thus, disinfectants are still required.
Many other viruses are resistant to heat and drying, too. PCV2 and porcine parvovirus are naturally resistant to environmental challenges, including heat and disinfectants, making pig transport still a significant biosecurity issue. It is difficult to implement practices that assure zero exposure between loads of pigs.
The water supply can be a major biosecurity risk if it comes from a surface source. On-farm purification systems are typically inadequate and don't supply potable water. Maintenance and operation of these systems are often neglected. Many agents can enter a system through the water including swine and avian influenza, PRRS virus, TGE virus, PCV2, leptospirosis and all enteric pathogens.
Next Page: Biosecurity Barriers
Biosecurity Barriers
Farm and system security are extremely important. Over the years, there have been many documented reports of pig thievery as a primary source of new disease entry into farms. It appears that these invasions often occur at multiple farms during the course of a single night, thus pigs are on the robbery transport vehicle from multiple sources, exposing each farm visited during the course of the night. Thieves aren't always just after pigs. Equipment and supplies are also targets, and pig farms are typically easy, low-risk targets. It is relatively simple to break into many farms in a single night.
Accidental disease entry may also occur if people enter a farm looking for employment or for other seemingly legitimate reasons. This situation occurs when there is no security against human entry. Warning signs are often overlooked, so lockable gates and doors that exclude entry during and after business hours are critical.
Perimeter fencing is more important for human exclusion than what was previously believed for domestic stock and wild animal exclusion. Although animal exclusion is important, people are the greater risk. Double security systems are best where the farm entrance has a lockable gate with a second, secured entry barrier at the barn entrance.
Showers are very good at preventing many disease agents. Enteric bacteria that are capable of infecting multiple species, such as salmonella, E.coli bacteria and other potential gut pathogens and most viral agents can easily be washed away. Detergent (soap) and water are tremendous barriers to new agent introduction, making a properly managed and designed shower entry a powerful deterrent for most swine diseases.
Other barriers, such as the “Danish” entry system, are also useful, but not as reliable as the shower facility. Boot exchanges prior to entering the shower area are adjuncts to the shower. They prevent tracking gross contamination into the shower area, but this space must be cleaned and disinfected routinely. Clothing change rooms are reasonable barriers, but don't reduce the risk of tracking as efficiently as the shower system.
Downtime rules have long been accepted by the swine industry as an effective method of risk reduction. The big question is, how long is long enough? For foreign visitors, they should be held out for at least five days after arrival in the United States. Many companies require a much longer period, especially for those visitors from high disease risk parts of the world. For most other service personnel, an overnight is enough if arriving in a clean vehicle, wearing clean clothing and entering through a shower protocol.
Food, especially fresh pork cuts, processed pork and any smoked meats are especially dangerous if they come from outside the United States. Classical Swine Fever (hog cholera), pseudorabies, and FMD viruses can survive in smoked products and are especially viable in any fresh pork product derived from an infected pig.
Feed products, feed trucks, and people associated with feed manufacture and delivery are potential risk factors, but generally are a much lower risk than many of the above issues.
Feed manufacturers should observe good manufacturing practices of biosecurity. Routine screening for bacterial agents, toxins and other risk factors, such as molds, should be in place. Feed truck drivers should not enter any of the farm buildings, including the office. Deliveries should be made from outside the perimeter fence. A “mailbox” ticket system outside the perimeter fence for feed receipts prevents driver entry.
Commercial and internal waste haul and management equipment and personnel can potentially move pathogens from site to site. They should never enter a farm unless it is empty of pigs. They should wash and disinfect all external surfaces of their equipment and observe all farm biosecurity rules. It is best to have biosecurity discussions during contract deliberations. Recently, there have been unconfirmed reports of swine dysentery introduction into farms from waste management equipment.
Airborne disease introductions are only recently quantified by research and field investigations. This area of biosecurity research is in progress. Again, agent ecology and exclusion technologies must be understood before fully assessing intervention technologies. This requires field demonstrations, which are underway.
There is little doubt that airborne spread occurs and has been documented with FMD and PRRS virus. Viruses that are very resistant in the environment, reach high replication levels, and have unique ways of entering air flows and wind currents (dust, water droplets etc.), are likely candidates for this method of spread.
Much research has been conducted with the PRRS virus, and it does not appear to be an efficient airborne agent compared to many other viruses. Nevertheless, circumstantial evidence has led many to believe this is a major route of new virus introduction. Area spread is most likely a combination of many routes and factors, leaving actual airborne introductions in a lower but significant risk category. Airborne spread is likely seasonal, increasing in cold, wet conditions, and is of great consequence in pig-dense areas.
Service personnel and outside vendors are generally low on the risk hierarchy unless they travel from pig farm to pig farm. They should observe downtime rules (overnight), arrive in a clean and sanitized vehicle, shower in and out, and visually inspect and disinfect all tools and equipment.
Service veterinarians must also abide by the biosecurity rules. Veterinarians, because of their extensive training in disease management and biosecurity, could be considered a much lower risk than most other vendors. Even so, they must always conduct themselves with great scrutiny and effort at preventing any new agent introduction, including the more innocuous disease opportunists.
Next Page: Internal Biosecurity
Medications and other supplies are very low-risk factors, but they should be considered. Introduction of these materials can usually be managed without adding much biosecurity expense, and the protocols are simple. Fumigation with disinfectants prior to entry is often the preferred method, but visual inspection and assurances from suppliers that no returned products will be delivered are likely all that is needed.
Preventing new disease introduction is not the only reason for biosecurity. As discussed in the general section, there are two components to biosecurity — internal and external. Internal biosecurity is all about disease agent management. We have numerous tools that are useful at those critical control points.
Internal biosecurity includes all the efforts that prevent or avoid disease expression caused by agents already present in the pig population. The following briefly discusses some of these methods, many of which are not routinely considered as part of the biosecurity plan.
One of the most important tools used in biomanagement is all-in, all-out (AIAO) pig movement, with proper cleaning and downtime between fills.
Multi-site production is an extension of AIAO. When managed with effective biosecurity standards, this is a more effective bio-management tool compared to single-site AIAO. When effective external biosecurity strategies are not utilized, then multi-site production will suffer due to the increased risk of new agent introductions through transport, specific area spread site risks and other additional inputs — especially personnel.
Although not often considered a part of biosecurity, vaccines and antibiotics are certainly a part of biomanagement.
Farm environment and ventilation are also biomanagement hazards to be continually monitored.
Piglet cross-fostering protocols are an additional biomanagement issue that is often overlooked. Excessive fostering can facilitate both PRRS and influenza viruses, allowing them to become a permanent disease presence in large breeding farms. Fostering should be limited to the first 24 hours after a sow farrows.
Hand washing is especially important in the farrowing room. Disposable gloves are a replacement for washing. Gloves should be changed between each litter during processing. Dirty hands or gloves easily track clostridium, salmonella and E.coli in the farrowing room.
Disinfectant-filled boot baths are of no value in bio-management. Good sanitation, room drying, hot water and detergent cleaning, achieving comfortable temperatures, and proper ventilation are the backbone of any bio-management plan.
The recent global episode of the novel H1N1 influenza virus, which rapidly spread among people, between countries and continents, is a preponderant reminder of the importance of zoonosis to a highly mobile, global society. Although the pandemic H1N1 had never been isolated in pigs prior to the pandemic, there is significant evidence that the virus had a direct or indirect pig background, most likely somewhere in Asia.
This event has certainly changed the way we think about influenza virus and has brought influenza to the forefront of our overall biosecurity and surveillance recommendations.
There are internal and external concerns, and our biosecurity tools to confront this virus are somewhat limited.
Up until the recent evolution of the H1N1 influenza, pigs have been an “end” host to human and bird (avian) influenza viruses. Most swine and human influenza experts suggest that the pig has been a regular recipient of human influenza viruses since 1918, and only rarely have the “new” pig viruses jumped species, returning to humans.
Thus, it is reasonable to make an effort to protect pigs from human seasonal influenza viruses. Unfortunately, traditional biosecurity safeguards, effective against many other agents, are of lesser value for human flu prevention. However, here are some steps to follow:
Support seasonal influenza and H1N1 vaccination of all farm employees and their family members.
Promote “stay at home” policies for workers when they come down with influenza-like illness (ILI). This will require education and sick leave reinforcement to employees so they can more accurately recognize early flu symptoms and respond accordingly.
Follow all the Health and Human Services (HHS) and Center for Disease Control (CDC) guidelines to prevent community spread of influenza. Frequent hand washing or use of sanitizers is recommended at home and inside the farm.
Ensure that shower-in, shower-out facilities with dedicated farm clothing and footwear are provided as a significant deterrent against many human- and swine-origin enteric bacteria and viruses that may ride in on wet or soiled clothing. It is scientifically documented that showers can prevent new agent introductions, possibly including human influenza viruses. Still, it is not likely that this is a main route of flu introduction, but is part of a complete biosecurity system.
Next Page: Internal Influenza Biosecurity
Any farm or site that utilizes surface water is at risk for bird influenza virus introductions. Surface water can harbor many infectious agents that can infect pigs and humans, including avian influenza viruses. Water for pigs should be potable and free of bacteria and viruses. When surface water is the only available water supply, it should be monitored monthly with coliform counts and other tests that assure its safety and purity. On-farm water purification systems should be continuously monitored and maintained.
On rare occasions, swine influenza viruses infect humans. Although this seems to be on the increase, it may be a result of better surveillance and identification by human diagnostic labs. Influenza is now a reportable disease for humans; thus, all non-typeable isolates are identified in influenza-like illness situations.
Preventing influenza spread from pigs to people is not well established. It occurs so rarely that the circumstances leading to human infection are not well understood. Even so, washing hands frequently, especially before smoking, using smokeless tobacco products and before eating is important. It is especially important to safeguard individuals who are immune-compromised or suffering from other illnesses. Children may be at greater risk due to unrecognized hygiene, and past and present exposure factors. Although the overall risk of human infection with a swine influenza virus remains extremely remote, these precautions should be considered:
Use of dust masks and disposable gloves are of limited value in preventing infection from pigs-to-human and human-to-human, but may be of some value in preventing spread from humans to pigs. The use of disposable gloves will not prevent the spread of human influenzas to pigs since they become contaminated as quickly as the skin they cover. In farms where hand washing is limited, disposable gloves can provide a barrier if changed frequently, but offer little advantage to hand washing. Good quality double-strap dust masks may be of some value in protecting pigs if changed regularly and properly disposed of, out of reach from pig contact. It is thought that influenza is spread by larger respiratory droplets, which a dust mask will collect, reducing contamination of hands, clothing and farm environment.
Novel H1N1 vaccines for pigs will arrive on the market in late 2009 to early 2010. These vaccines should be highly effective since U.S. pigs have yet to be exposed. These killed vaccines should be focused on the growing pigs and avoided in breeding herds under most circumstances. Studies where the novel H1N1 is used in pig challenge, the lesions and clinical signs are similar to swine influenza, but are not considered mild. The pig H1N1 vaccine should reduce disease severity, virus shedding and clinical disease, but will not likely yield significant cross-protection against current swine influenza viruses.
In general, all-in, all-out movement of growing pigs, proper vaccination timing, hot water and detergent cleaning between groups are documented to reduce both viral and bacterial loads in the pigs' environment. It is important to recognize that disinfectants supplement the cleaning process and are not a primary means of sanitation within the farm. They are extremely important in transportation risk reduction, and most will destroy influenza viruses.