An outbreak of a potentially deadly equine herpes virus that has affected 18 horses in California has kept ticket sales for the Memorial Day Classic, a weeklong riding show at the Los Angeles Equestrian Center in Burbank, at about half of what they should be, according to a spokeswoman for the event.

All 18 horses affected by the equine herpes virus-1, a highly contagious airborne virus, were placed under quarantine, according to the California Department of Food and Agriculture. No new cases have been reported since May 23.

Humans are not at risk of contracting the virus, for which there is no vaccine.

But misinformation about the virus and its outbreak has kept many visitors away from the weeklong show and competition, which doubles as a fundraiser for the Toluca Lake-based nonprofit racehorse rescue, After the Finish Line, said Marnye Langer, a spokeswoman for the event.

“It is impacting the show in a very negative way, but we are confident that we are not placing any horses at undue risk,” she said.

The virus was found in two horses at a May 13 cutting horse show in Bakersfield and in 16 California-based horses that participated in the National Cutting Horse Assn.’s Western National Championships April 29-May 8 in Ogden, Utah, according to the Department of Food and Agriculture.

Horses became ill after coming in contact with an apparently sickly horse that participated in the cutting events. Horses affected by the virus typically show some signs of fever, lethargy, nasal discharge, hind-limb weakness and lack of coordination, according to the department.

Local Veterinarian David Ramey has been warning horse owners to not panic about the virus, which he said tends to pop up when horses are put under heavy stress.

“The reaction is so far out of proportion as to the actual risk to the horse,” he said.

Organizers planned to monitor and investigate any signs of illness displayed by participating horses at the event, said George Chatigny, general manager of the equestrian center.

Langer advised riders to “take a deep breath” and read up on facts from the veterinarians about the virus.

“We are still encouraging the public to come,” she said.

Event organizers have reduced the price of VIP tickets to boost attendance, she said. Those tickets will cost $25, or six for $125, plus one seat for free.

The show will feature horse jumping, cricket and a riding competition for a $25,000-purse at the Memorial Day Grand Prix.