A leading expert on the PRRS virus at the University of Minnesota says his research team has pinpointed the essential biosecurity tools.

The pork industry has known how to eliminate the PRRS (porcine reproductive and respiratory syndrome) virus from hog farms since 2000.

The catch has been in identifying ways to control area spread of the virus to protect negative farms from regularly becoming reinfected. That quest has become a big part of Minnesota veterinarian Scott Dee's research focus.

Dee spent much of his 12 years in private practice on developing control strategies for on-farm PRRS infections. Eight years ago, he joined the University of Minnesota, serving as co-director of the Swine Disease Eradication Center, and leading efforts toward unlocking the secrets to area spread of PRRS.

He has been a strong proponent that the pork industry needs to set a course of PRRS eradication (See: “The New War on PRRS,” National Hog Farmer, June 15, 2006, page 34.).

Speaking at the first Pijoan Lecture during the Leman Swine Conference (named after Carlos Pijoan, DVM, University of Minnesota, who passed away last December), Dee summarized his research evidence.

PRRS Components

Fomites, the mechanical means of transmission of the PRRS virus, are responsible for more frequent occurrences of virus spread in cold weather than in warm weather. Producers can reduce risk of disease spread by changing boots, coveralls, washing hands, showering and incorporating 12 hours of downtime between pig contact periods, according to Dee.

The use of disposable footwear and gloves and double-bagging products for entry into farms greatly lessens the level of PRRS contamination and mechanical spread of the virus, he says.

Contaminated transport vehicles have definitely been implicated as a source of PRRS virus infection for naïve pigs, and drying is a key element in maintaining biosecurity.

Insects have been shown to be mechanical, but not biological, carriers of the PRRS virus. Their control can be enhanced using a combination of screening of the air inlets of hog units along with the use of targeted insecticides and habitat management.

The role of aerosol spread in PRRS transmission has been debated for many years, and has proven to be “the toughest nut for me to crack,” says Dee. When his first research project failed to reproduce aerosol spread, a graduate student showed him that the frequency of shedding and transmission of the virus could be strain-dependent.

In later studies, using PRRS strain MN-184, documented for its high frequency of aerosol spread, Dee was able to show that the risk of aerosol transmission was reduced by air filtration.

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