The Maryland Department of Agriculture on Thursday placed a hold order on a barn at Laurel Park after a 2-year-old filly tested positive for equine herpesvirus, a highly contagious disease that has surfaced several times at racetracks in Maryland over the past two years.\nThe filly, Nin, who is trained by King Leatherbury, could not stand on Wednesday, according to state veterinary officials, but was eating on Thursday with no sign of fever. None of the other 29 horses in the barn was showing any neurological signs of distress, the officials said.\nThe filly tested positive in tests conducted by the University of Maryland, according to Julie Oberg, a spokeswoman for the agriculture department. Because the test is new, however, officials have sought to confirm the findings with further tests at the University of Kentucky. Those results will be returned by Friday afternoon, Oberg said.\nThe hold order will prevent any horses in the barn from coming into contact with other horses on the backstretch. The horses will not be able to leave the barn for racing or training.