A sick horse trained at Fair Grounds by Dallas Stewart has tested positive for the equine herpesvirus, leading to a quarantine of all horses in a barn shared by Stewart and trainer Neil Howard, and restrictions on horses shipping into and out of Fair Grounds, the track announced Friday.\nThe horse in question, a filly named Diamond Song, got sick earlier this week, and was subsequently shipped to Kentucky, where she tested positive for the herpesvirus, which is highly contagious and can cause fever and upper-respiratory distress in horses.\nThe quarantine affects some 70 horses trained by Stewart and Howard. Horses from these two trainers will be allowed to train only during a designated time slot in the morning, when no other horses are out on the track. Quarantined horses cannot be entered to race until they twice test negative - with the tests performed one week apart - for the virus, and are cleared by Dr. Tom David, the Louisiana State Racing Commission's equine medical director, according to Eric Halstrom, vice president and general manager of racing.\nHorses shipping in to race at Fair Grounds must go directly into the Fair Grounds receiving barn during the quarantine period. Also, with one exception, Fair Grounds-based horses cannot ship elsewhere to race while the quarantine is in effect. Fair Grounds horses will be allowed to race at Delta Downs, provided they ship into the stakes barn and leave directly from it.\nAs of Friday afternoon no other horses had shown signs of illness, though all horses in the infected filly's barn were undergoing tests, Halstrom said. Diamond Song, who is housed at the Rood and Riddle Equine Hospital near Lexington, Ky., was reportedly recovering.