Diagnostic tests done at the University of California, Davis, have confirmed that a euthanized horse stabled at Santa Anita Park, in Arcadia, Calif., was positive for equine herpesvirus-1.

On March 5, My Sugar Sugar, an unraced 3-year-old filly trained by Eddie Truman, required euthanasia after developing neurologic signs. There have been no other reported cases of EHV-1 at Santa Anita.

According to a statement from the California Horse Racing Board (CHRB), My Sugar Sugar had been feverish four days earlier and developed neurologic signs on day four. Biosecurity procedures were implemented that day and the California Department of Agriculture was notified of a suspected case of EHV-1.

The average incubation period for EHV-1 is 4 to 7 days, with the majority of cases being 3 to 8 days, but with some taking up to 14 days. All horses in the stable are being closely monitored and none of the others has exhibited signs of fever or illness