BATON ROUGE, La. — The entire New Orleans Fair Grounds race track has been placed under quarantine to block the spread of an equine herpes virus.

The virus, called EHV-1, is latent in many horses, but symptoms can emerge periodically, at which point it becomes contagious. Symptoms include fever, nasal secretions, poor balance, anorexia and aborted pregnancies.

State veterinarian Dr. Brent Robbins announced the quarantine late Thursday, noting that nine horses remain in isolation.

Louisiana Agriculture Commissioner Mike Strain says that although there’s been restricted movement of horses at the track, the state can’t risk any leaving while some are still testing positive for the virus.

The quarantine began in a barn where two horses tested positive Dec. 28.