NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

January 21, 1999

NDSU Researchers Take Aim at Costly Swine Disease

By looking at how a costly and incurable swine virus replicates itself, North Dakota State University researchers hope to uncover clues about how to control the disease.

Lynn Rust and Eugene Berry, researchers in the veterinary and microbiological sciences department, recently received nearly $50,000 from the U.S. Department of Agriculture to study how the Porcine Reproductive and Respiratory Syndrome (PRRS, pronounced purrs) virus changes as it reproduces.

The disease was first diagnosed in North America and Europe in the late 1980s and early 1990s. It is rapidly transmitted by contact and results in abortion, stillborn piglets and weak litters. Infected adult pigs that survive the acute stage of the disease may succumb to secondary infections or suffer reduced production. Because infections do not always result in disease outbreaks and can easily be misdiagnosed, and because the virus changes so rapidly, researchers have had difficulty assessing how widespread the problem is, but they agree the cost to the swine industry is in the millions of dollars. Farms with chronic PRRS infections can see profits cut by up to 70 percent.

Rust says the PRRS virus reproduces very rapidly. "In organisms like humans, cellular replication is a slow, painstaking process with an emphasis on accuracythere's not much change in genetic make-up from one generation to the next. But in these viruses, the emphasis is on speed, so there are a lot of changes and mutations that occur," she notes.

Those changes make it difficult for researchers to develop diagnostic tools or vaccines. The mutations short-circuit their efforts.

Rust and Berry will be studying the most basic biological processes that occur when the PRRS virus replicates. Researchers have identified one protein, an enzyme, necessary for the virus to multiply, although other proteins, derived both from the virus and from the pig, are known to be involved. "The protein factors seem to determine how fast replication occurs and how many mistakes are made," Rust explains.

They'll also be studying the genetic code of the virus itself, looking for sequences of genes that remain stable as the virus mutates. "If we can isolate those sequences, we may be able to develop diagnostic tools for them or they may be a focus for therapy," Rust says.

Some strains of the virus replicate and change at different rates than others. Rust and Berry will be comparing strains to find out why since the speed of replication correlates with disease severity.

The USDA seed grant will support two years of research. If results are promising, it's likely the USDA will funnel additional resources into the project and related work.

Rust says the NDSU work will be investigating the most basic interactions between the PRRS virus and its host. "The applied research often comes out of the basic investigations like this," she says. "The more we know about this disease and how it works, the more tools we will have in the future to monitor and control it."

Assisting Rust and Berry are research assistants Dawn Doetkott and Chad Zimprich, and master's degree candidate Crystal Shanley.

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Source: Lynn Rust (701) 231-7848

Editor: Tom Jirik (701) 231-9629