The outbreak of equine herpesvirus-1 (EHV-1) at Hawthorne Race Course, near Chicago, Ill., appears to be under control, but remains under close watch, according to a Dec. 19 statement from assistant manager Jim Miller.

In the statement Miller said that 18 days have passed since the last EHV-1-related death at the racetrack, and some horses that previously tested positive have retested negative. Those horses have been moved back into their barns from the quarantine area, he said.

"We have … recently had some asymptomatic horses that have been tested and tested positive for EHV-1," he said. "Those horses have been required to be relocated to a quarantine location until they test negative."

"Horsemen have been asking when the quarantine will be lifted," Miller said in the statement. "There is no firm date