In today's pork industry, perhaps no issue is as critical to protecting and maintaining the health and efficiency of swine herds as a scientifically based program of biosecurity.
Infection of susceptible swine with agents such as porcine reproductive and respiratory syndrome (PRRS) virus , Mycoplasmal pneumonia and swine influenza virus, in conjunction with pathogens such as Actinobacillus pleuropneumonia and Hemophilus parasuis, can lead to the formation of the porcine respiratory disease complex and result in reduced performance, elevated mortality and reduced profitability.
In addition, intestinal pathogens such as Lawsonia intracellularis , Transmissible gastroenteritis (TGE) virus and Escherichia coli negatively affect survivability, growth rate and feed efficiency. Preventing the introduction of these agents through a science-based biosecurity program is a critical component of a farm's disease control program.
This article will summarize the rationale behind the protocols of swine herd biosecurity, review routes of pathogens spread between farms and provide data from scientific studies that support the application and practice of specific protocols.
These protocols continue to be tested and validated through an ongoing experiment at our Swine Disease Eradication Center (SDEC)  production region model farm in west central Minnesota. This farm is using PRRS virus and Mycoplasmal pneumonia as model agents. It is well known that the cost of a PRRS break is anywhere from $5-15/pig or $250/sow.
Our hope is that swine veterinarians and their clients can work together to utilize this information for the development of effective biosecurity programs for sustainable disease control.
Direct Routes of Pathogen Spread
It is well known that infected animals and/or contaminated semen can introduce infectious agents to susceptible populations. Depending on the agent, once introduced to a herd, pathogens can be shed by carrier animals via blood, saliva, milk and colostrum; urine and feces; and by contaminated semen.
Purchasing genetic material from naÏve sources that are monitored on a regular basis is critical to a successful biosecurity program, as is proper use of scientifically validated quarantine and testing protocols.
Ideally, quarantine facilities for incoming breeding stock should be located on a separate site. Incoming stock should be kept separate from resident stock for a minimum of 30 days and farm personnel should monitor animals daily for clinical signs of disease. The herd veterinarian should remain in close communication with the seedstock supplier's veterinarian during this period, in case the onset of a disease is suspected in the source population or the animals in quarantine.
During the quarantine period, animals should be blood tested according to veterinary recommendations.
Indirect Routes of Pathogen Spread
Pathogens spread through indirect routes include contaminated facilities, fomites (i.e., needles, boots, coveralls), people, transport vehicles, pests and aerosols. Examples supporting these conclusions, as well as protocols to reduce the level of risk, are as follows:
Facilities — Swine facilities should be managed using all in-all out (AIAO) pig flow, thereby reducing the spread of PRRS virus from older, infected pigs to younger, naÏve animals.
In conjunction with AIAO flow, it is important to properly sanitize the facilities before introducing susceptible animals. All organic material (feces, urine, feed, bedding, body fluids) should be completely removed and the surfaces carefully washed.
Once clean, an efficacious disinfectant should be applied throughout the pen area. The application of disinfectants using a foamer allows for better visualization of where product has been applied and also prolongs the contact time between the chemicals and the surfaces. Allow adequate time to dry.
Fomites — For pathogens that replicate and/or circulate in the bloodstream, injection of consecutive animals using a contaminated needle can result in blood-borne spread of certain viruses, such as PRRS and possibly porcine circovirus Type 2 (PCV2) .
To reduce this risk, it is recommended that producers change needles between sows during third trimester injections or utilize “needle-free” technology.
Contaminated containers, such as semen coolers, tool boxes and cartons of farm supplies, along with coveralls and boots, can serve as mechanical vehicles for PRRS virus spread.
Consequently, all incoming supplies should be disinfected and double-bagged prior to entry into a designated room on the farm. Barn-specific coveralls and boots should be available in all facilities and washed routinely. Disposable coveralls and boots are another option.
Use of footbaths can greatly reduce the risk of transfer of certain pathogens, such as PRRS virus, between groups of pigs. Footbaths should be changed daily to maintain disinfectant efficacy. Only disinfectants that have been validated as efficacious should be employed.
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Transport Vehicles — Pathogens such as PRRS virus and TGE virus can be spread to susceptible animals following contact with contaminated transport vehicles.
That makes cleaning, disinfecting and drying key elements in sanitizing the trailers, with drying being the critical component of the process. Potential risk points in the cab of the truck (pedals, floor mats, etc.) can be effectively sanitized using disinfectant spray.
Personnel — Barn workers can harbor pathogens on their hands (PRRS virus) and in their upper respiratory tract (swine influenza virus). Protocols to reduce the risk of pathogen spread via farm personnel routes include farm-specific periods of off-site sick time (recommended 1-2 nights), Danish entry and shower in-shower out.
Pests — Insects (house flies, mosquitoes) as well as rodents can serve as mechanical vectors of pathogens and do significant damage to facilities.
Insects have been shown to carry PRRS virus and TGE virus, while rodents can harbor Brachyspira hyodysenteriae, the causative agent of swine dysentery.
Institute a monthly program of pest control, preferably through a professional exterminator. In addition, producers should properly manage the habitat of these pests to reduce their ability to perpetuate.
Control of vegetation and placement of crushed rock around facilities, along with the use of pyrethrin-based insecticides and pit additives, are all beneficial to achieving this goal.
Aerosols — The airborne spread of pathogens, such as PRRS and Mycoplasmal pneumonia, is well documented out to at least 2.8 miles.
The use of an air filtration system may be essential to prevent infection of susceptible populations by these agents, particularly when they are housed in swine-dense regions. The ability of air filtration systems to significantly reduce the risk of airborne spread of PRRS virus, in general, and between farms has been well documented under controlled field conditions (Table 1). Similar results have also been observed in boar studs and large sow farms in swine-dense regions of the United States.
The decision to install an air filtration system depends on the individual producer's budget, the location of the site (high swine density vs. low density), the level of acceptable risk and type of production system (i.e. seedstock or commercial).
Commercially available filters that utilize mechanical, antimicrobial or electrostatic technologies (MERV 14 or MERV 16) can be installed in facilities utilizing negative-pressure ventilation systems in various ways, including filters on ceiling inlets or a filter bank preceding the cool cell pad. A pre-filter is used in conjunction with the filter bank to maximize the lifespan of the primary filter.
Since swine farms in the United States traditionally employ negative-pressure ventilation, all potential air leaks (cracks in the building, around windows and doors, shutters and idle fans) need to be caulked and sealed at all times.
In addition, double-door entry/exit systems with air lock doors must be installed to prevent potentially contaminated air from entering the animal air space at high-risk points, such as personnel entryways, live/dead animal loadout rooms, etc. These latter two points are discussed in the sidebar on page 9.
Miscellaneous — Additional routes of indirect pathogen transmission, which may be important for producers to consider when developing their farm-specific biosecurity protocol, include fresh pork, lagoon effluent and a means of handling dead animals. Meat from infected pigs can harbor PRRS virus for at least seven days at refrigerator temperatures and for months when frozen.
Transmission of PRRS virus secondary to the consumption of infected meat or meat juice has been well documented. Consequently, fresh or frozen pig meat should not be allowed in a swine facility at any time.
PRRS virus can also survive in lagoon effluent for 3-8 days, and contact with PRRS-positive effluent can serve as a source of infection to naÏve pigs. Therefore, producers who utilize recycled lagoon water in their waste management protocols may be at higher risk for external virus introduction than those who use deep pits.
Finally, PRRS virus can be inactivated through composting or incinerating carcasses. Only these methods should be applied. Allowing rendering trucks to drive onto farm premises should be avoided at all times.
Based on our experience over three years, the protocols summarized here are highly effective at preventing pathogens such as PRRS virus and Mycoplasmal pneumonia from being spread to susceptible pigs.
Obviously, personnel compliance is the key to successful implementation of these procedures. Veterinarians can play an important role, not only as the team member who delivers science-based biosecurity to the farm, but also as a teacher to educate personnel and as an auditor to ensure compliance.
By practicing these protocols, it is hoped that producers can effectively reduce the risk of pathogen introduction to their herds and maintain a high standard of swine health and production on their farms.
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A broad application of a comprehensive biosecurity program across farms may also aid in reducing viral spread within a region, and enhance the success of area-based control and eradication programs.
|Replicates||Airborne Infections (filtered)||Airborne Infections(non-filtered)|
|Year 1||26||0||8 (PRRS virus only)|
|Year 2||13||0||6 (PRRS virus)/7 (M hyo)|
|Year 3||9||0||6 (PRRS virus)/3 (M hyo)|
|Note: Because the model involved PRRS virus only in Year 1, replicates were two weeks in duration in Year 1. Replicate length was increased to four weeks in Years 2 and 3 due to the use of a M hyo-PRRS virus coinfection. Only nine months of data were available for Year 3 since the study was still in progress. Filter type used in Years 1 and 2 consisted of MERV 16, while Year 3 utilized two filtered facilities, one which was equipped with MERV 14 filtration, while the other utilized antimicrobial filters.|
Auditing Enhances Biosecurity Efforts
Once a biosecurity program has been established, it must be well-managed in order for it to be successful over time.
Swine veterinarians can play a major role in enhancing a program's success through a regular program of auditing.
Components of a biosecurity audit consist of developing written standard operating protocols and training staff through experiential learning opportunities, along with a regular walk-through of the facilities.
The latter is particularly important for monitoring the presence of air leaks or back drafting of non-filtered air through idle fans in
Security cameras and perimeter fencing are also helpful in monitoring day-to-day activities of personnel as well as detecting/preventing unwanted visitors from entering swine farms.
— Scott Dee, DVM
Double-Door System Protocols
The protocol of the double-door system involves the use of a chamber and specific procedures as follows:
The chamber must contain an external door and an internal door that corresponds with the animal air space. When entering from the outside, the external door is opened, personnel or pigs enter a chamber and the door is closed. The same process occurs when entering the chamber from the inside of the building using the internal door.
The chamber must also contain an exhaust fan designed to clear all the air in the room in a certain time frame, from 1-5 minutes, depending on room volume.
To aid in evacuating contaminated air, “clean” air is drawn into the chamber via a baffle inlet from an anteroom (an outer room that leads to another room) or an animal air space within the facility.
Once animals/personnel have entered the chamber and both doors are closed, the fan is turned on and allowed to run for the designated time period.
Once the evacuation period is over, the interior door can be opened, allowing personnel/pigs to enter the facility or leave the facility via the external door.
Note: The double-door system has been extensively tested and found to be highly efficacious at preventing the introduction of virus via contaminated aerosols, both at the Swine Disease Eradication Center (SDEC) production region model in west central Minnesota and on filtered commercial farms in the Midwest.
It is important to work with an experienced agricultural engineer to determine the proper fan size and evacuation period according to the volume of each chamber.
— Scott Dee, DVM