BOISE, Idaho (AP) - Horse owners and organizations nationwide are watching anxiously and shutting down shows and other events in an effort to keep a deadly horse virus outbreak that began in Utah from spreading beyond a handful of Western states and Canada.

So far, at least 17 horses in Idaho, Utah, Colorado, California, Washington and Canada have been infected with the highly contagious Equine Herpes Virus-1, and at least three have died. The disease poses no threat to people but is easily spread among horses, alpacas and llamas because it can be airborne and transmitted by touch or by sharing feed, brushes, bits and other equipment.

The infected horses were among roughly 400 that attended the National Cutting Horse Association Western National Championships in Ogden, Utah, earlier this month.

Now, officials in several states are quarantining infected animals and asking owners of other horses that were at the event to closely monitor the animals for symptoms. Organizers also are cancelling horse shows, festivals and classes in Texas, Utah and elsewhere in an effort to stem the disease's spread.

The outbreak has horse owners across the West worried, said Preston Skaar, president of the Idaho Cutting Horse Association.

"It's a hard deal, but all you can do is have your horses stay home and wait it out," Skaar said.

He took one horse to compete at the Utah event and then brought it back to his property in Menan, Idaho, where it lives with 12 other horses. So far, he said, none of the animals have shown any signs of illness, but he's starting each day earlier so he can take their temperatures and check for fever, gait problems and other symptoms of the virus.

Infected horses can appear perfectly healthy until they get stressed and the virus takes hold, he said - so none of the horses are being ridden unless absolutely necessary.

"I was kind of bummed out that I didn't make the finals (at the Odgen competition), but I'm not feeling quite as bad about it now," Skaar said. "That kept my horse from getting more stressed and fatigued, and maybe that helped."

Officials with the National Cutting Horse Association couldn't be immediately reached, but a statement on the organization's website said the group is closely monitoring the situation and that all NCHA-approved shows scheduled for this weekend have been canceled by the affiliates or show producers putting on the events.