Even with the successes of filtration in preventing the introduction of porcine reproductive and respiratory syndrome (PRRS) and other aerosolized pathogens into swine populations, we still have a way to go with the implementation and execution phases.
Air filtration systems are rapidly expanding, but practical application will take time. Adjustments will have to be made when failures occur and disciplined procedures must be reviewed and refined if we are to achieve daily success.
In our practice area, 99% of the sow barns are curtain-sided and, thus, filtering them with the technology we currently have requires the sidewalls to be enclosed. We continue to look for practical air filtration barriers, such as Plexiglas and removable or hinged doors. Yet, these options present challenges because as the static pressure in a building increases, any introduction of non-filtered air presents a risk.
Reducing Risk is Vital
As we work through adaptation of filtration over broader areas, we should not lose sight of the body of research that gives us direction on how to minimize introduction of the PRRS virus. Producers must be vigilant about implementing proven biosecurity strategies to lower the risk of pathogen introduction. Important barriers and procedures for a sow unit include:
1. Personnel entrance. All personnel entering the sow unit should remove their outside coat or other apparel and shoes in a designated dirty area. This is most conveniently accomplished by marking an area with tape or paint and utilizing a bench to sit and remove shoes. When shoes are removed, avoid placing stocking feet in the designated dirty area. Swing your body around and over the bench, avoiding any contact with the floor. A 4-in. elevation of tri-bar or wire mesh for the dirty area is also advantageous because it allows shoes and boots to drain into a collection area. An alternative is to use a rubber or plastic container to retain outside footwear.
2. Food. Lunches brought to the facility should enter through a double bag system, so the outside bag can be removed in a designated area within the entry foyer. The inside bag or lunch box is then placed in an ultraviolet (UV) light area used for inactivation of the virus through a UV-C germicidal light (wave length of 253.7 nanometers). Ultraviolet light neutralizes viruses, bacteria and parasites on common farm surfaces and materials by disrupting the nucleic acid and preventing further replication, according to research published by University of Minnesota veterinarian/researchers Scott Dee, DVM, (now with the Pipestone, MN, Veterinary Clinic), Satoski Otake, DVM, and John Deen, DVM. The six easy steps to remember are:
• Put lunch boxes in the UV light area.
• Turn on the UV light.
• Shower in.
• Leave the light on for 10 minutes total from the last box.
• Turn the light off.
• Remove lunch box.
3. Showering. All personnel should follow the basic showering procedures and utilize only the clothing provided by the unit.
4. Breeding stock. All incoming breeding herd replacements should come from a PRRS-negative source and be isolated with statistical sampling for the absence of virus. The diagnostic tests used will depend on the time interval from entry to sampling. Samples should not be taken for at least two weeks post-arrival.
Utilize both the polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). PCR is an antigen test and ELISA is an antibody test. The PCR will become positive 24-48 post-infection and the ELISA within 10-14 days. The PCR requires certain primers and may not always detect a new strain, while the ELISA will detect the strain. If sampling is done prior to this time interval, the number of samples should be increased to ensure a statistically significant sample is evaluated, since the value of the ELISA decreases because of the time required for development of detectable antibodies.
5. Replacement stock. Replacement animals in quarantine should have a standardized care procedure, and these facilities should be shower
in/shower out. The quarantined population should be on a lockdown until the diagnostics are obtained and reviewed by the farm veterinarian.
6. Semen origin. Semen should come from a filtered boar stud with an accepted statistical sampling procedure to establish the absence of PRRS virus. Semen should be delivered to the disinfectant chamber in a double-bag system. To avoid crossover traffic, courier staff should not enter the entry foyer of the sow unit. As an alternative, semen can be delivered to an off-site cooler so a farm staff person can transfer the semen into the disinfectant chamber.
7. Supplies/equipment. All supplies and equipment should enter through a designated disinfectant chamber and/or cleaning process. No equipment that has been repaired off the farm should be allowed into the farm without proper screening procedures both at the site where the repairs were made and at the unit where they will be used.
8. Pig exit. All pigs exiting the sow facility must pass over a clean/dirty threshold to ensure no over-and-back, crossover traffic occurs. The clean/dirty threshold will vary depending on the facility. Generally, the threshold is a door or gate at the end of the loading chute. No outside personnel should be allowed to cross the clean/dirty threshold. Likewise, no inside personnel should be allowed to cross the clean/dirty threshold.
Live animal removals of weaners, feeders and cull sows should be handled using the same procedure. Dead animal removal should also follow this procedure, transferring the animal over the designated clean/dirty line where an outside farm staff member removes the mortalities to a designated area.
9. Feed, feed trucks. Feed has not been shown to be a high risk for PRRS spread, although the truck it is transported in poses the same level of risk of carrying virus-contaminated snow, sludge or mud as any other staff vehicle. In fact, feed trucks have a much higher risk of contamination compared to staff vehicles because they commonly transport feed to multiple sites. Because of this, the truck driver should wear a designated pair of boots that are put on as he leaves the cab of the truck and removed before he reenters the cab.
10. Manure application. Manure handling and disposal represent several different risks. Recent work suggests that PRRS virus lives in the effluent for seven days. Some in-barn cases suggest the virus may live for longer periods, which may be due to the conditions within the effluent. Manure handling equipment is inherently difficult to clean and disinfect and application often requires several pieces of equipment. And manure applicators are frequently under weather constraints that further hamper the ability to maintain downtime after cleaning and disinfection.
Follow these practical steps to reduce contamination by equipment:
• Require each farm to have its own equipment that goes into the pit.
• Never permit the manure pumping and application crew to enter barns.
• Construct temporary pit covers over the pit fan pump-out area to prevent additional rainwater, birds or rodents from entering.
11. Water. Many sow units are supplied by surface water. Water generally provides a large dilution factor and the exact risk is not quantified. Water should be treated with common treatments such as hydrogen peroxide or chlorine dioxide. Concentration and contact time are critical.
PRRS virus remains very active within our pig populations. The swine industry has a tremendous amount of scientific data to guide producers and veterinarians in how to practically manage and prevent the introduction of the virus. Still, the virus continues to adapt, so traditional barriers may not be satisfactory. We must continue to put all of our industry resources into eliminating this virus.