For four swine veterinary practitioners speaking at World Pork Expo last month in Des Moines, PRRS virus has been a consuming interest.

In a packed seminar sponsored by the American Association of Swine Veterinarians (AASV), Paul Ruen, DVM, the association’s president, recalls PRRS came on the scene in the late 1980s as Mystery Swine Disease when he was in veterinary school at the University of Minnesota. It has continued to perplex producers and veterinarians alike since then.

“PRRS has affected everything we do on farms, and it is the number one concern all the time,” says Ruen, staff veterinarian at the Fairmont (MN) Veterinary Clinic. Identified in the early 1990s, it can cause reproductive problems such as abortions, stillborns and mummies.

But Ruen says most of the problems his clinic sees come in the grow-finish period. “The immune system is compromised with respiratory problems, causing pneumonia, and affected pigs look like they will just fall apart and won’t eat.

“We are doing a lot better job of stabilizing farms more quickly than we used to, using tools to handle pig flow and get the break knocked down more quickly. The sooner you do that, the faster you can get to weaning (PRRS) negative pigs, and the less likely you are to contaminate the neighborhood,” he continues.

Yet you can be doing everything right on the farm and still become infected due to aerosol spread of the virus, Ruen says.

Attacking Aerosol Spread

Aerosol spread of PRRS virus has become the primary research focus of Scott Dee, DVM, who has spent over 20 years immersed in the disease, working at a Minnesota veterinary clinic and for the last 5-7 years focusing on transmission and biosecurity studies at the University of Minnesota.

His new research data confirms that PRRS virus can travel 5.7 miles through the air, plotted from 300 infected pigs in a continuous-flow production system at the University of Minnesota’s swine research farm in west central Minnesota.

Since work started there in 2006, there has been no infection of any pigs in the buildings where air filtration systems have been installed, he says, whereas non-filtered control barns have experienced airborne spread of either PRRS virus or Mycoplasmal pneumonia about 40-50% of the time.
In five years studying 25 boar studs in southern Minnesota that are filtered all year, all have remained negative for PRRS, mycoplasma and swine influenza virus, Dee confirms.

Granted, boar studs are easier to manage with air filtration than sow farms, which are a lot bigger, often older, involve more people and have more turnover, and therefore create more challenges to filtration systems, Dee says.

“In regards to sow farms, research is ongoing to test the filtration technology in large sow farms in swine-dense regions,” Dee says. “While preliminary data looks promising, more time is needed before any conclusions can be drawn.”

The cost to filter a sow farm has dropped from around $250/sow to an average of $141/sow. Therefore, the cost of air filtration can be paid for by preventing one PRRS break, Dee points out. He says producers shouldn’t give up just because they don’t think they can afford to install an air filtration system.
“Doing something is better than doing nothing, because you can still reduce your risk of becoming infected,” he assures.

Quest for PRRS Elimination

In 2001, the 116,000-sow Cargill Pork system attempted a PRRS elimination program in approximately 150 contract sow farms in Missouri and Arkansas.

“The goal was to be PRRS-free by 2003, and we succeeded,” remarks David Nolan, company veterinarian based in Russellville, AR.

“We threw everything we could at PRRS during that eradication effort, and the result was a phenomenal success,” he reports. Sow herds were stabilized by closure, positives were rolled out and negative gilts were brought in. Pigs/sow/year (p/s/y) blossomed by more than two p/s/y for the system to a respectable 22 p/s/y by 2004, and continues to improve. Nursery culls and mortality rates that had been 10% or higher were cut in half.

“It is important to stop the flow of gilts and boars into the herd during cleanup. Do your testing and know where you are at,” Nolan advises.

By 2008, the system had been humming along PRRS-free for about five years when a small break occurred in two sow farms that share a composter. Tornadoes and the accompanying winds were blamed for the spread from a local PRRS-positive farm 1.8 miles away. The herds were depopulated and repopulated and have remained PRRS-negative.

However, in early May, a new Cargill contract sow farm in Missouri and two other farms broke with PRRS. The outbreak appeared to start in some finishers that have since suffered extreme clinical disease. The virus quickly spread to a farm four miles away. Then the third farm 6.8 miles away broke with a very hot strain of PRRS, which has been killing every baby pig in the farrowing house for the first three weeks, Nolan says.

There has been no connection between the three farms except for suspected aerosol spread of the virus. “You never know what you are going to get with a PRRS break — a mild or a severe strain,” he says.
Importance of Biosecurity

Rodney “Butch” Baker, DVM, senior clinician in Veterinary Diagnostic and Production Animal Medicine at Iowa State University, has worked on numerous PRRS eradication efforts while at PIC and at Premium Standard Farms, plus consulted in Cargill Pork’s efforts.

There are three biosecurity components necessary for PRRS cleanup:

1. Bio-management — controlling the diseases that are present. For PRRS, these measures may include vaccines, live virus inoculation, herd closure, etc. Limit crossfostering and introduction of new stock.

2. Bio-exclusion — keeping new viral disease agents out of farms through truck washes, trailer baking, downtime rules, showers and air filtration.

3. Bio-containment — stopping disease spread. “As producers, it is our ethical responsibility to practice bio-containment. Those are the things that we try to do to avoid tracking the virus to our neighbors,” Baker says.

“We can’t stop aerosol spread of the virus, but there are a lot of other things we can do to slow this virus down. We can shower out of a facility, take off our farm clothes and shoes and put on clean clothes and shoes before we go to the coffee shop in town or visit our neighbors,” he says.

Breaking Down Biosecurity Risks

Biosecurity risks break down into two categories, says John Waddell, DVM, Sutton (NE) Vet Clinic, speaking at the Boehringer Ingelheim Vetmedica, Inc. (BIVI) media seminar on PRRS at World Pork Expo.

Direct biosecurity risks include live animals and semen, which 10-20 years ago were frequent causes of disease introduction, but are now rare occurrences because of advances in testing and monitoring, he says.

The indirect causes of disease transmission, such as aerosol, transport and personnel, are still areas of concern.

Strict sanitation is needed in barns and in transport vehicles to block potential virus spread. Gating, fencing and loadout mechanisms must exclude visitors, truckers and trailers from reaching the inner sanctum of high-health status farms, Waddell explains.

Downtime only needs to be one night. Changing boots and coveralls and washing hands are more important than showering. This Danish system creates a line/barrier from dirty to clean in the barn that can work well to stop disease spread, he says.

The AASV PRRS Risk Assessment tool developed by BIVI has been a tremendous benefit in educating producers on risk factors for introduction of PRRS virus, Waddell says. Several areas need to be addressed to assure successful elimination of PRRS:

  • Determining true persistence of the PRRS virus in a herd. Small studies have shown the virus can persist in pigs for months, but persistence in larger herds needs to be studied.
  • Identifying safe separation distance to prevent aerosol spread, including the risk to pig farms near roadways where PRRS-positive pigs are traveling.
  • Assessing the risk of PRRS virus in effluent and the risk when manure is being pumped out of a building or onto fields.
  •  Improving the accuracy of polymerase chain reaction tests in detecting the PRRS virus, and reducing the cost and turnaround time of PRRS virus genetic sequencing.

Area Control Projects

Also at the BIVI seminar, Dee briefly outlined PRRS area regional control and elimination projects. From their successful start in Stevens County, MN, projects have cropped up in Colorado, Illinois, Indiana, Michigan, Nebraska, Pennsylvania and Ontario, Canada. A project is in the early planning stages for Iowa County, IA.

The projects take a “big picture” approach to disease control by calling for collaboration of producers and veterinarians. This process calls for understanding disease status across farms, as well as the risk factors that promote virus spread, to improve disease control within an area or region.
The projects start by eliminating PRRS virus on farms in low-prevalence and low-density swine areas, and progress to control of PRRS in high-prevalence, high-density areas. The goal is to improve pig performance by reducing incidence of field virus in control areas and reducing the long-term risk of those viruses returning to PRRS elimination areas, Dee says.

Jean Paul Cano, professional services veterinarian with BIVI, says PRRS vaccine can play a critical role in reduction of PRRS infections as part of area regional control.

“Research shows the use of vaccine has direct benefit when used to mitigate the clinical consequences of infection, and improves the health and performance of pigs,” he says. “In addition, we’ve learned vaccinations have indirect benefits in reducing the level of virus and virus transmission within vaccinated populations.”

Mass vaccination can be a complementary tool in an area regional control program, along with a herd closure strategy, a gilt acclimation program and appropriate pig flow and biosecurity protocols, he says. “Vaccine can provide protection and biologic and economic benefits when PRRS-naïve pigs are placed into high-prevalence areas for finishing,” Cano comments.

Dee concludes that thanks to advances in PRRS research and industry tools, there is enough information to make a dent in controlling this devastating disease.

“The most effective and successful PRRS control and prevention within an area requires a high degree of cooperation, coordination and collaboration within and among production systems in a region,” he says.