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National Hog Farmer

PRRS Cloud

PRRS Cloud
Approximately 20-plus years into the fight to rid the nation of porcine reproductive and respiratory syndrome (PRRS) virus, a more realistic approach may be to improve efforts to control the persistent disease.

Approximately 20-plus years into the fight to rid the nation of porcine reproductive and respiratory syndrome (PRRS) virus, a more realistic approach may be to improve efforts to control the persistent disease.

That’s the message from Scott Dee, DVM, PRRS researcher and director of research at the Pipestone (MN) Vet Clinic, in a talk at the Minnesota Pork Congress last month in Minneapolis.

In 2005, Dee wrote a position statement for the American Association of Swine Veterinarians calling on the swine industry to attempt eradication of PRRS.

The ‘New Norm’ of PRRS?

Dee says the first indication that the PRRS virus may have changed occurred in 2011, when Pipestone Veterinary Clinic research reported elevated levels of airborne PRRS virus around farms.

“The driver for this investigation was reported setbacks of regional PRRS control projects,” he says. These projects are now at a crossroads.

“With what happened in 2011-2012, and is continuing in 2013, suggests that the epidemiology of PRRS virus may have changed,” Dee says.

The PRRS researcher says some facts are becoming clear about the “new normal” of PRRS:

• The airborne spread of this virus is increasing. It is challenging traditional, tested, airborne biosecurity measures such as farm location and filtration.
• Air sampling during March 2012 indicated there is increased virus frequency and quantity and diversity of virus challenge around swine barns.
• This work was repeated in October-December 2012.
• There are multiple variants of PRRS virus floating around these farms, so it is likely they are constantly under challenge, almost like an air raid perspective.

To deal with this new challenge, Dee suggests three options that groups can take: collaboration, filtration and vaccination.


Producer groups must continue to collaborate on regional control projects, sharing data for PRRS outbreaks, and testing their farms at producer expense to learn their true status.

“We might need a more realistic mindset, especially for producers in dense regions, a mindset of control instead of elimination,” Dee observes.


Air filtration is not a silver bullet against PRRS, he stresses. “Air filtration does one thing and one thing only — it reduces the risk of virus introduction through the airborne route. It is only a tool; it is not right for all people and it is not perfect,” he says. Key points:

1.    Air filtration can be overwhelmed if a significant challenge occurs.
2.    Filtration systems are dynamic, changing over time and aging very quickly in the challenging environment of the pig barn.
3.    Check and maintain prefilters and filters. Make sure the spray foam around filter boxes is intact and that filter clips are still properly holding filters in place.


More farms that are PRRS-negative will want to vaccinate for PRRS to reduce their risk of infection, he predicts.

“I think we need a vaccinated negative herd classification scheme for our farms. We have got a number of farms that have taken this approach in our (Pipestone) production system to reduce the economic loss should infection occur,” Dee explains. They are still considered “negative” farms to wild-type PRRS, but use modified-live vaccines (MLV) to help reduce risk.

“MLV PRRS vaccination is a tool to protect yourself as well as your neighbor. It is a tool that has advantages in area control projects that should not be ignored,” Dee says.

The researcher also anticipates that PRRS testing at veterinary diagnostic labs can be expedited to speed turnaround of results in sequencing the strains of the virus to better understand virus movement in an area.

Dee urges producers to maintain constant oversight of their operations. “Train people, watch them, make sure they are following the rules. Check the filter system daily and regular biosecurity measures.”

He closes with two key messages:

• As the virus changes, so must we.
• Support your state veterinary diagnostic laboratory.

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