A pair of connected barns at the New Orleans Race Course was quarantined Friday because a 3-year-old filly tested positive for equine herpes.

It may take 10 days to clear other horses trained by Dallas Stewart, who trains the filly, and Neil Howard, whose barn is connected to Stewart's, said Dr. Tom David, the equine medical director of the Louisiana State Racing Commission.

Stewart has about 40 horses at the track and Howard 26. All are being tested and may not race until they are cleared, said Eric Halstrom, the Fair Grounds vice president and general manager of racing.

Stewart said the filly in question, Diamond Song, worked five furlongs Monday morning. "She didn't look right on Monday afternoon - her equilibrium, the functions of her back legs," he said.

He sent her Tuesday to Rood and Riddle Equine Hospital in Lexington, Ky., and learned of the positive test Wednesday. The track was closed for training Thursday for Christmas, so all horses stayed in their barns.

David said the virus can be transmitted through the air or by direct contact. It usually affects the respiratory system but can infect the brain, he said.

Two tests are required, David said. He said results from the first are available in 48 hours but it takes about a week to get results from the second.

The Fair Grounds has changed its training schedule to keep those horses away from all others. It is open from 5:30 a.m. to 9:30 a.m. for all other horses. From 9:30 a.m. to 10:30 a.m., Stewart's and Howard's horses can be trained.

In addition, horses stabled on the track's backstretch cannot leave the grounds until the horses in question are cleared - with one exception. Horses may be shipped to Delta Downs, as long as they go directly to the stakes barn there and leave from that barn.

To avoid the quarantine for backstretch stabling, horses racing at the Fair Grounds can be shipped to and leave from its receiving barn.

Howard says the horses in his stable all look fine.

Stewart said, "We've got to hope that the horses remain healthy. They're saying that the filly should be able to recover and be able to race again."

Diamond Song has raced twice, winning her debut Oct. 25 at Keeneland and finishing eighth in an allowance turf race Nov. 13 at Churchill Downs. Monday's workout was her fourth at the Fair Grounds this month.