When it comes to preventing the spread of the porcine reproductive and respiratory syndrome (PRRS) virus, precautions need to extend to anyone who comes within infectious range of your operation — including your custom manure applicator.

Minnesota research is helping veterinarians develop strategies to help manure applicators keep the virus from hitching a ride on equipment during manure pumping and hauling operations.

PRRS spreads in a variety of ways, including through sow’s milk, saliva, semen, blood, urine and feces. The virus is also capable of traveling up to six miles through the air. These factors combined make the virus easy to spread but difficult to battle.

Research has shown the PRRS virus can survive for up to six days at temperatures of 70°F. and for years when frozen. However, the virus seems to be particularly successful at thriving and spreading in cold, damp environments, which makes fall and early winter the “high season” for PRRS spread.

Dave Wright, DVM, Buffalo, MN, says the PRRS virus has been shown to survive up to 11 days under cold and wet conditions. Therefore, the risks of spreading the virus when swine manure pits are being pumped and the slurry applied are increased. “This is a problem, because usually manure application is done in the fall when it is cold and wet, which makes it a great time for PRRS transmission,” he says.

PRRS Viability

Daniel Linhares, DVM, at the University of Minnesota, recently investigated how long the PRRS virus could remain viable in swine manure at different temperatures. He compared the half-life of the PRRS virus in manure to similar survivability in a cell culture medium. Half-life is the amount of time it takes for half of the virus to die off, thereby reducing its potential to be infectious.

Linhares found an exponential decrease in PRRS virus infectivity with increasing temperatures. While the half-life of PRRS virus in manure was 112 hours at a refrigerator temperature of 39.2°F., it dropped to 14.6 hours at room temperature (68°F) and only 1.6 hours when manure was close to body temperature (104°F.).

Wright says Linhares’ results could be used to develop strategies to inactivate PRRS virus present in a manure-contaminated environment.

Precautionary Steps, Protocols

Through his work on a Minnesota PRRS elimination project, Wright acknowledges that some producers are reluctant to admit they are battling PRRS. But he stresses the importance of sharing information about a farm’s PRRS status so producers and manure applicators can work together to plan routes that will help decrease the risk of spreading the virus.

If manure applicators know their customers’ PRRS status, they can modify their schedules to handle manure from PRRS-negative sites before positive sites, clean equipment thoroughly between jobs, and allow enough downtime for the virus to become inactive. Another option is to alternate between jobs at dairy operations and swine operations. PRRS does not affect other animals, so there is no danger of spreading the disease to a dairy herd, he explains.

Wright says manure applicators should encourage producers to test for PRRS. For planning purposes, “it is good to know a site’s PRRS status before you go onto the farm. If they break with PRRS after you leave, you could be blamed for the outbreak even if PRRS was already on the farm. If you don’t know the PRRS status of the site, treat it as though it is positive,” he advises.

In addition, Wright encourages manure applicators to ask pork producers to share any biosecurity protocols before they arrive at the job site. “Ask if they have specific, written biosecurity procedures in place that they would like you and your employees to follow. If the producer doesn’t bring it up, it is your job to ask for it,” he says.

Manure applicators must respect a farm’s biosecurity rules at all times. “Producers don’t want anyone to walk into barns or entryways. A lot of producers would rather not even have you walk next to a curtain-sided building. They don’t want manure application vehicles close to buildings, especially not in the vicinity of doors where debris could be tracked into the building.”

Before arriving at the farm, manure applicators should provide a schedule for the on-farm personnel. “They may want to monitor or modify ventilation, for example. If they have an employee on-site who needs to shower in and out in order to help you, the producers and employees should know that ahead of time,” Wright says.

Producers expect manure applicators to show up with clean equipment. “Some operations may have a checklist and may ask the manure applicator if they can inspect their vehicles and equipment prior to arrival. Some producers might even look inside your truck to see if you have a lot of debris on your floor mats,” he notes.

Vehicles, the pump and undercarriage should be free from material. All personnel coming onto the farm should wear clean clothes, shoes and boots.

Manure applicators should not travel between hog farms during pit pumping and application jobs. If another farm must be visited during the job, the manure applicator should shower and change into clean clothing and boots beforehand.

Wright suggests starting manure application as far away from the hog buildings as possible, preferably at least one mile or more for the first 10 loads. “The goal is to minimize the risk that the PRRS virus may be traveling in the manure or equipment from other production units by unloading at least the first loads as far from the building as possible. Of course, be aware of neighboring hog units, too,” he adds.

After pit pumping and application are complete, equipment cleanup should not take place near hog buildings or in high-traffic areas. Some producers may dedicate a hose or pressure washer for cleanup. “Make sure you are not leaving debris in an area where it could be tracked into swine buildings,” Wright says.

When equipment is clean, allow it to dry completely to minimize the likelihood of providing the damp environment in which the PRRS virus can survive.

Regional PRRS Project

Because of the highly infectious nature of the PRRS virus, it only takes a small amount of virus to infect an entire herd. A persistent infection can last up to 200 days in some pigs. Unfortunately, because the PRRS virus mutates easily, it is difficult to find a consistently effective vaccine to help control the virus. It is better to try to prevent an outbreak than to treat one, he emphasizes.

Wright is spearheading a regional PRRS elimination project in Minnesota. Since 2004, the voluntary, producer-led control program has had a goal of eliminating PRRS through producer education and communication efforts. Wright works with pork producers to develop strategies aimed at controlling the spread of the virus in their area. “Taking the necessary steps to minimize the risk for spreading PRRS is really critical,” he reinforces.