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The definition of biosecurity is “the protection/security of susceptible animal herds from the introduction and transmission of infectious pathogens”. The concept of biosecurity has been long considered essential to swine producers and veterinarians. However, its importance is recently becoming even more significant because of the impact of PRRSV. Examples of biosecurity protocols currently practiced in swine farms for prevention of PRRSV introduction are as follows:
1. Quarantine and testing of incoming pigs
2. Testing of semen
3. Fomite sanitation
4. Shower-in/out of facilities
5. Transport vehicle sanitation
6. Air filtration
1. Quarantine and testing of incoming animals
Since direct contact between infected and susceptible pigs is the principle mean of introduction of PRRSV into farms, quarantine (isolation) and testing of incoming stock provides a safeguard against this route. Quarantine allows time for producers/veterinarians to observe new stock for disease clinical signs prior to herd entry. Blood-testing should take place during the quarantine period to have confirmed information regarding infection status of the incoming stock. It also gives them the opportunity to acclimatize or vaccinate incoming stock against current herd diseases. With the consideration of potential risk of disease transmission via unknown routes, quarantine units have been highly recommended to be isolated from the herd and ideally to be located on a different site. Finally, the quarantine/isolation unit should follow a specific management routine. The unit should be the final building visited each day, and movement of personnel and equipment between the unit and other herds should be restricted. Hygiene practices, such as waste handling or carcasses disposal, should be managed separately from the main herds.
2. Testing of semen
Besides infected pigs, semen has been also considered as a risk factor for the introduction of PRRSV into susceptible herds. Therefore, testing semen for these organisms prior to use in breeding herd is critical to minimize the risk of pathogen introduction. Microbiological analysis of semen is challenging. Bacteria in semen are generally numerous, resulting in contamination of cell culture systems for virus isolation and overgrowth of special media for growing fastidious organisms such as Mycoplasma spp. Recent application of the polymerase chain reaction (PCR) assay has improved in the detection of microorganisms from semen by allowing us to overcome such potential problems with virus/bacteria isolation procedures, and has become the standard method for the detection of PRRSV in semen.
3. Fomite sanitation
Since PRRSV has been detected on contaminated fomites, the changing of clothes and boots on farms has been routinely practiced to reduce pathogen transmission via such routes. The use of boot baths containing 6.5% sodium hypochlorite has been shown to be effective for sanitizing boots contaminated with PRRSV, both in the presence and the absence of feces. The risk of PRRSV entry to farms on the surfaces of contaminated containers (semen coolers, toolboxes, pharmaceutical shipments, etc) has resulted in the establishment of “product quarantine” facilities. In these specific buildings and/or rooms, products scheduled to enter the farm are sanitized with disinfectants known to be efficacious against PRRSV and are allowed to overnight prior to entry. Disinfectants frequently employed consist of glutaraldehyde/quaternary ammonium chlorides or peroxygens.
4. Shower-in/out of facilities
Prior to entry to the herd and following exit from the herd, taking a shower in a designated area of the facility has been considered a standard biosecurity practice and is widely implemented in North America. Studies have demonstrated that changing contaminated clothes/boots and taking a shower prevented the transmission of PRRSV from infected to susceptible pigs. Another option is the Danish system, where the changing clothes/boots and hand washing in designated area is required. Finally, these methods not only limit physical movement of personnel, but also provides a barrier to discourage visitors who do not have a compelling reason to enter the herd.
5. Transport vehicle sanitation
It is now accepted that trailers contaminated with PRRSV can serve as a source of infection for naïve pigs. Therefore, sanitation for livestock trailers and transport vehicles is considered a high priority when it comes to biosecurity practices. There is a variety of protocols practiced in the swine industry to minimize transport risk; however, the primary principles are disinfection using an efficacious product and drying. The trailer should be at first washed with hot high-pressure water to remove all visible contaminants. It is important to understand which type of disinfectant to choose and its respective disinfection period. As mentioned earlier, glutaraldehyde/quaternary ammonium chloride products or peroxygens have been proven effective when applied using a low pressure foamer and given a 2-hour period of contact. Drying is essential for inactivation of PRRSV, and some breeding companies and integrated production companies have recently developed procedures using forced heat air to dry trailers, which are referred as Thermo-assisted drying and decontamination systems (TADD) or “trailer bakers”. These procedures have recently been evaluated scientifically and appear to be highly efficacious.
6. Air filtration
Air filtration has been widely applied to farms in France and Quebec, Canada and is gaining popularity in the US. Following the discovery that PRRSV isolate pathogenicity may be a major risk factor for PRRSV spread via aerosols, air filtration of boar studs has been applied widely throughout the US and is now being tested in sow herds. Evaluation of air filtration in a model of a swine production region has indicated the ability to protect susceptible populations of pigs from the airborne spread of the virus for extended periods (approximately 2 years). Methods to filter air range from HEPA filtration using positive pressure to the use of lower cost filters applied to negative pressure facilities. In recent studies, it appears that alternative filtration systems exist, such as the use of 95% at 0.3 micron DOP (MERV 16) filters. Due to its significantly lower cost when compared to HEPA systems, if proven to be efficacious, the application of air filtration could be wide-spread across all phases of production, thereby enhancing regional clean up programs. These filters also appear to prevent airborne spread of other agents, such as Mycoplasma hyopneumoniae and field reports indicate that filters may last for over 2 years before needing to replaced. Further studies are underway to evaluate whether other means of filtration, such as anti-microbial filters or MERV 14 filters may be cost-effective alternatives, thereby reducing the expense of the intervention and improving the animal environment during periods of warm weather.