Shedding Light on Mystery Pig Disease

Quick diagnosis of a virus that kills unborn and new-born pigs can help reduce losses for U.S. pork producers.

In 1987, a disease of pigs appeared so inexplicably in the United States that it was dubbed "mystery pig disease." Soon after, it spread throughout the world.

For 4 years, it remained a deadly enigma, until Dutch scientists identified a virus as the cause of the disease that is now called PRRS—porcine reproductive and respiratory syndrome.

PRRS virus produces flu-like symptoms in pigs of all ages. Pregnant sows infected with the virus can abort, or farrow a few days early, bearing litters of dead fetuses and piglets. Even though they look healthy, some pigs that recover are carriers of PRRS virus and spread the disease.

A team of ARS researchers at the National Animal Disease Center in Ames, Iowa, have been studying the PRRS virus to develop better methods for its diagnosis and control. Veterinary medical officers William L. Mengeling and Kelly M. Lager, along with microbiologist Ann C. Vorwald, have devised a more accurate way to detect the virus in infected pigs.

Up to now, blood tests have been used most often to identify pigs with PRRS virus. But these tests are often negative—even when used to evaluate an infected pig.

The new test finds the virus in lung cells long after it disappears from the blood. These lung cells, called alveolar macrophages, can be easily and safely collected from live pigs.

"It's reliable enough to detect carriers of the virus, as well as to diagnose the acute disease," says Mengeling.

The economic impact of PRRS is still unknown, but many researchers consider it to be one of the most costly diseases faced by the swine industry. A recent survey of Midwestern pig farms showed that 50 percent of the pigs had been infected with the virus. Losses from PRRS have been estimated to range from $50 to $250 per affected sow per year.

Others on the NADC research team studying PRRS include veterinary medical officer Susan L. Brockmeier and technicians Deborah S. Adolphson and Theresa E. Rahner. — By Linda Cooke, ARS.

Kelly M. Lager is in the USDA-ARS Virus and Prion Diseases of Livestock Research Unit, National Animal Disease Center, 2300 Dayton Ave., Ames, IA 50010; phone (515) 663-7371, fax (515) 663-7458.

"Shedding Light on Mystery Pig Disease" was published in the November 1995 issue of Agricultural Research magazine.