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PORK TAB - Research advances made in determining how disease spreads

By Gary Gunderson

gunder@agrinews.com

ST. PAUL -- The last 18 months have seen great advances in determining how Porcine Reproductive and Respiratory Syndrome Virus is spread by mechanical means such as needles and contaminated clothing.

More work is needed to see if the disease is spread by animals, soil or through the atmosphere, according to a University of Minnesota veterinarian.

Scott Dee, with the university's Swine Disease Eradication Center, said work on the role birds, insects and inanimate objects play in spreading PRRSV is still being conducted. But enough information exists for farmers to protect their operations from PRRSV by installing insect screens on sidewall openings in facilities; using disposable boots at truck wash sites; disinfecting vehicle floor mats and personnel boots; and by developing ways to prevent packages from spreading the disease.

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Research the center has conducted indicates that the roles birds and the atmosphere play in spreading PRRSV has been over-stated, while insects and inanimate objects such a soil need more study, Dee said.

The center continues to study all possible transmission routes to help solve the mystery of how PRRSV can spread to farms that have eliminated infection through hogs delivered to the farm and semen.

Current studies the center is conducting include:

Exposing Mallard ducks to PRRSV-infected hogs and drinking water. The ducks will then be housed with PRRSV-free hogs for 14 days to see if the disease is transmitted from fowl to hog. Past studies have shown that PRRSV-contaminated water can infect ducks, and the ducks can carry PRRSV determined to be infectious to hogs.

Ten PRRSV-free hogs will be subjected to exhaust from a trailer containing 150 PRRSV-positive hogs for seven continuous days.

Studies have shown mosquitoes and houseflies transmit PRRSV. The center's study will determine if the virus is carried internally by the insects, or whether it's on the outside of their bodies.

The extent of PRRSV spread by soil particles, specifically measuring the impact of heat and dryness in spreading the disease.

There may be a connection between infections and outside temperatures, because a majority of the 12 boar studs in multiple states that became infected with PRRSV during cold spells in late 2001 and early 2002, said Joseph Condor, a veterinarian with Carthage Veterinary Service in Carthage, Ill.

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