Summary

Currently, there is little science validating the effectiveness of biosecurity procedures; but the base of knowledge continues to expand. Veterinarians are encouraged to approach biosecurity protocols as one would approach protocols for medication and vaccination. Protocols should be based on actual risk, not fear. Biosecurity procedures should be strategically implemented based on risk assessment of individual farms. Farm personnel should participate in the development and implementation of procedures to improve buy-in and compliance. One should expect variability in the effectiveness of procedures due to differences in livestock, personnel, and premises. Once implemented, protocols should be regularly monitored for compliance and efficacy. Practices should be modified as scientific advances are made in the field and as new pathogens emerge. Practices that are not effective, or not cost-effective, should be eliminated.

Introduction

Perhaps a better title for this article should be ‘stopping new bugs from getting in’ or ‘stopping too many of the old bugs from getting in,’ or ‘how to achieve the impossible on a long-term basis.’ In truth, there would be no need for this article, or veterinarians, if there were scientifically proven, effective measures for preventing the entry of pathogens to livestock populations. However, in the long term, the chances are that pathogens are going to get in. Pathogens simply win in terms of numbers, genetic diversity and the capacity to rapidly adapt to changing situations. Each year the human population tries to outguess the influenza virus and select which vaccine strains will be most appropriate. How many times is it correct? Many bacteria can double their population every 20 minutes. Months can pass before veterinarians can get biosecurity protocols approved and implemented on a farm. The goal of this first of two articles is to discuss biosecurity procedures that can reduce the risk of pathogens from entering a swine farm. The science of biosecurity is in its infancy; therefore most of the ideas presented should be considered opinions that are based on science when possible.

There is no universal biosecurity protocol that all farms can implement to minimise the risk of pathogen introduction; just as there is no universal vaccination or medication policy that is effective for all swine farms. Each farm is unique in terms of location, facilities, host susceptibility, management, and infectious disease pressures, to name a few. Thus biosecurity is a continual process of assessing individual farm risks, identifying and prioritising risk abatement procedures, implementing biosecurity protocols according to need and cost, evaluating the effectiveness of such protocols, and eliminating, modifying, or adding biosecurity procedures as critical areas of risk change.

Taking inventory

The first step in developing an effective biosecurity program is to identify what pathogens are enzootic to the herd. (Ridding the herd of enzootic pathogens will not be discussed in this series). If possible, prevalence, morbidity, mortality, and herd-specific costs of each pathogen (prevention, treatment, control measures, performance effects, etc.) should be estimated. This list will become the baseline for establishing the efficacy of biosecurity protocols to keep additional pathogens from entering the herd.

Setting goals

The next step in assessing risk on an individual farm is to identify the target pathogens needed to be kept out of the herd. The target pathogens should be prioritised. The prioritisation will vary from herd to herd. Factors used to prioritise pathogens include the probability of infection, susceptibility of the herd to the pathogen, economic impact of infection, product of herd (genetic stock versus meat). Examples of prioritisation:

Example 1 - Probability of infection: A herd might have transmissible gastroenteritis virus (TGEV) higher on the priority list and foot-and-mouth disease virus (FMDV) lower down. Even though FMDV would be more devastating to the herd, the probability of TGEV infection is usually much greater than FMDV.

Example 2 - Susceptibility of the herd to infection: A herd that is genetically resistant to Escherichia (E.) coli infection would not prioritise E. coli as a pathogen to prevent from entering the herd.

Example 3 - Economic impact of infection: If an infection with a pathogen would result in low morbidity/mortality in the herd and there were effective and inexpensive control or treatment measures then that pathogen might be lower on the priority list. For instance, keeping out Actinobacillus pleuropneumoniae might be a higher priority than keeping out Mycoplasma hyopneumoniae.

Example 4 - Product of herd: A gilt multiplier herd might have porcine reproductive and respiratory syndrome virus (PRRSV) as a top priority because they guarantee PRRSV-free genetic stock to their customers.

One would hope that good biosecurity programs would be effective enough to prevent a broad range of pathogens from entering the herd. However, targeting specific pathogens provides some advantages: (1) Pathogen characteristics can be used to design the most effective protocols for prevention of that specific pathogen; (2) The efficacy of established protocols can be measured based on prevention of targeted pathogens; (3) The chance that money will be spent on unnecessary or impractical tangential protocols is minimised.

Assessing risks to an individual farm

After the targeted pathogens have been prioritised, the most likely source of these pathogens can be assessed. Potential sources of pathogens include: aerosols, genetic stock, semen, feed, water, people, manure, vehicles, other fomites, domestic and non-porcine feral animals, feral swine, rodents, insects, and birds.

A review of the literature allows potential sources of infection of some common swine pathogens to be summarised. The summaries have been divided into animal/animal products (Table 1), and non-animal sources (Table 2). In some cases, the pathogen was detected under naturally occurring circumstances. In other cases, the supposed potential source of infection was experimentally inoculated with the pathogen and designated a potential source of infection if the pathogen was subsequently detected in or on the potential source of infection. Domestic and feral swine were excluded from the summaries and should be considered a potential source of all porcine pathogens.

Identify which potential sources offer the greatest risk of pathogen introduction to the herd

Next, external sources of pathogens can be ranked to identify which sources that can be controlled offer the greatest risk to the herd of interest. Frequency of contact with the source, level of pathogen contamination of the source, and duration of survival of the target pathogen in or on the source can be considered. Pathogen characteristics and survival times can be gleaned from the scientific literature. Farm surveys can be used to establish frequency of contact. Swine herds with greater than 2000 pigs in California reported that they were contacted by people and vehicles that had contacted other livestock facilities between 374.9 to 1239.5 times per month with an average indirect contact rate of 807 times per month (Bates et al, 2001).

A large consideration at this point is which of the potential sources of pathogens can be realistically controlled. For example, farms located within 2 km of greater than four other farms were almost three times more likely to experience two or more respiratory disease outbreaks per year than farms located within 2 km of less than or equal to four other farms (Rose and Madec, 2002). Although the risk of pathogen introduction is greater in a swine dense area, location cannot be controlled unless one is building a new unit. Another example would be that the manager of an outdoor farm in an area populated by feral swine might not be able to control contact among the domestic and feral swine. Thus feral swine might offer a greater risk of disease introduction than healthy new genetics entering the herd. Once again, the risk rankings will vary from farm to farm.

Determining the extent of the biosecurity program to be implemented

At this point, the biosecurity focus has been narrowed to specific pathogens from specific sources enabling the establishment of a biosecurity program with some direction. The program can be as simple as implementing a strategic vaccination program to build the herd's immunity to a specific pathogen or as complex as constructing new facilities for isolation of new stock.

The extent of the biosecurity program will most often be determined by the level of risk that the herd owner is willing to accept. Some people have risk-taking personalities and might not wish to implement even the simplest biosecurity program until an epizootic forces the point. Others are not accepting of even the slightest risk and will go overboard implementing every possible biosecurity procedure whether needed or not. Most people will have personalities falling somewhere in between the extremes. One must understand the viewpoint of the client when attempting to justify the appropriateness of the biosecurity program. The economic status of the farm is the next factor that will greatly impact the nature of the biosecurity program. One must determine how much is available for financing biosecurity procedures. Of course, the level of expenditure will be determined by the amount of available funds. However, the cost of a disease should the herd become infected can be estimated and used as a ballpark number for the amount that can be reasonably spent in disease prevention. Procedures that demonstrate the best financial return to the investment should be implemented.

For example, the absolute prevention of aerosol transmission of pathogens to a herd is not realistic under commercial conditions in a swine-dense area. The owner of a commercial herd in such an area will not be able to realistically or cost-effectively control the risk of aerosols as a source of disease. Thus, the owner would be wise to assume the risk of aerosol transmission and invest his money in disease prevention strategies such as vaccination to boost herd immunity to potential aerosolised pathogens. The owner of a nucleus herd would better spend his money by relocating to an area far from other swine or manure spreading areas even though this cost would exceed the costs of vaccination. Finally, a laboratory located within this area that cannot afford relocation might invest in HEPA-filtration units to abate the risk of aerosol transmission. Each unit will establish a program based on the risks and consequences of disease introduction for that specific unit. An effective biosecurity program for one farm might seem completely inane if implemented on another farm.

Identification of risk abatement procedures

Some common biosecurity procedure options are listed.

Aerosol transmission

• Locate in an area at least 3.2 Km from other swine or manure spreading locations. Distance will vary according to characteristics of targeted pathogens.
• Locate barns away from public roads.
• Maintain relative humidity < 60%, and optimise ventilation systems.
• Vaccination to build herd immunity to aerosolised pathogens

• Operate a closed herd
• Limit the number of genetic sources
• Introduce semen instead of boars
• Veterinarians of the source herds (semen suppliers) and recipient herds should work together to determine the health status and testing procedures to minimise risk of disease introduction.
• Aggressive selection, observation, and testing of new genetics with implementation of isolation and acclimation protocols.
• Isolation facilities should be located outside of the main farm premises. Stock in isolation should be cared for by a designated caretaker at the end of the day. The caretaker should not return to the main herd without showering and donning clean outerwear. The duration of isolation will vary and should be based on the maximum known shedding period for the pathogen(s) of concern.

• Limit entry to essential personnel
• Provide site-designated clean outerwear
• People that have contacted other livestock (including livestock kept by employees at home) should be required to shower to remove all visible contamination from their body prior to entry.
• Hand washing and donning clean outerwear will lower the contamination level of personnel but might not prevent transmission of all pathogens. Note that alcohol-based hand sanitisers are not effective on visibly contaminated hands. Wearing gloves can decrease the gross contamination of hands but does not prevent the need for hand washing.
• There is little evidence to defend restrictions regarding contact among personnel working at different swine farms as a biosecurity practice.
• There is little evidence to require animal avoidance periods (downtimes). However, people actively infected with zoonotic agents (i.e. Salmonella or influenza virus) should be denied entry to swine units until they are no longer shedding organisms.
• Secure the site from intruders.

• Install perimeter fences and gates to prevent vehicles from entering the premises.
• Limit entry to clean vehicles only.
• Utilise/install a nearby, off site, truck washing facility.
• Visitor parking and livestock trailer parking should be at least 300 m of the livestock buildings (Hege et al, 2002).
• Utilise farm and species dedicated livestock transportation vehicles.
• Utilise a perimeter transfer facility for selling animals. Farm-owned vehicles can deliver the animals to the loading area on the farm premises side and then livestock transport trailers can load swine from the facility without entering the farm premises. The transfer facility can be cleaned and disinfected in between loads.
• Locate feeds bins just inside of perimeter fencing to enable feed deliveries without having feed trucks on farm premises.
• Sequence vehicle movement such that vehicles only move from the healthiest sites to the least healthy sites.
• Rendering trucks should not be allowed on premises.

• Use disposable items whenever possible.
• Eliminate or minimise sharing of equipment among premises.
• Visibly contaminated fomites should not enter the livestock areas. All visible contamination should first be removed from the fomite to be disinfected. Disinfectants should be selected according to reported efficacy against target pathogens. Disinfectants should be prepared and applied according to label directions. The contact time recommended on the label should elapse. Aerobic bacterial counts can be used as a guideline for cleaning effectiveness. No more than 1 cfu/cm² of aerobic bacteria should be present following disinfection.

• Limit animal species on premises to human beings and swine.
• Perimeter fencing, trapping, etc can be used to limit contact with wildlife.
• Store and dispose of carcasses properly and promptly to minimise the attraction of scavengers.
• Good hygiene (removal of trash, feed spills, stagnant water etc.) and grounds maintenance (mowing, use of perimeter rock) can limit the attraction of rodents, birds and insects to the farm. However, professional exterminators should be utilised to implement or establish effective pest control programs utilising chemicals, baits, traps and other tools.

• Utilise quality control measures to minimise contamination of feeds and ingredients with pathogens.

• Do not allow manure from other swine facilities to be spread, sprayed or injected within 3.2 Km of the swine facility

Prioritisation of risk abatement procedures

Use the characteristics of target pathogens, potential sources, economic considerations, and personal risk acceptance levels to select and customise preventive procedures for each target pathogen under specific herd conditions.

Evaluating the effectiveness of procedures

Existing and newly implemented biosecurity procedures should be periodically evaluated for effectiveness. The innate efficacy of the procedure in preventing the introduction of target pathogens as well as employee compliance in implementing such procedures should be evaluated. As a result, failure due to a faulty protocol can be distinguished from failure to implement an effective protocol. Herd health monitoring utilising clinical signs, serology and post-mortem examinations can be used to detect clinical and sub-clinical exposure to target pathogens. Record-keeping and discussions at employee meetings can be used to evaluate compliance issues. Improved performance as a result of implementing protocols can be used to justify continuing or discontinuing the procedures based on costs. The biosecurity program will need to be adapted by eliminating, modifying, or adding biosecurity procedures as critical areas of risk and targeted pathogens change over time.

Glossary

Biosecurity: "security from transmission of infectious diseases, parasites, and pests." (W.B. Saunder, 1999).

References