A herd of wild horses captured near Haines Junction, Yukon, will have to be destroyed - government officials say all five animals have an incurable infectious disease.

The small herd has been running free for years in the Canyon Creek area west of Whitehorse. But this winter they started hanging around the Alaska Highway corridor where they became a traffic hazard.

No one knows who owned them, and since their capture last month no one has made a claim. Now tests have confirmed all have a deadly disease called equine infectious anemia.

Agriculture supervisor Kevin Bowers said federal regulations leave few options.

"It's a disease that there's no cure for and we have some tough decisions to make about euthanizing those horses as a result of their positive test results," Bowers said.

He said the small Canyon Creek herd was remote enough that it likely did not infect other free-ranging horses in the region. At least a dozen more animals, in two separate herds, still roam the Takhini Valley west of Whitehorse, Bowers said.

He said quarantine was not an option.

"Unfortunately the circumstances for permanant quarantine, the horse has to remain on that premise, it has to be secured against infecting other horses, neighbours, notifications, all those kind of things," Bowers said.

"So maintaining that quarantine is just beyond the caapacity of the government or any individual."