The National Cutting Horse Association Western National Championship in Ogden, ran from April 30 to May 8.
Equine Canada said the infected horse did not attend the Utah show "but was in direct contact with the horses attending the above stated show before they left Canada".
It said the horse has been under veterinary care and is recovering well. It is in no danger.
The origin of the source of contact for this horse remains unknown.
As of May 18, there was one yearling in Alberta confirmed positive for EHV-1 which showed only respiratory signs of the disease similar to normal influenza infections.
This horse was in direct contact with tack from the horses returning from Utah. It is under treatment and isolation and is in no danger at this time.
There is an additional confirmed positive case of a horse returning from Utah which showed a mild transitory respiratory disease. This horse is under isolation and treatment and is in no danger.
There are six to eight tests pending on horses similar to the above horse, which have attended the Utah show and have experienced mild respiratory disease.
"We expect some of these horses to have a positive test."
In British Columbia, three horses at a single farm who attended the Ogden show are suspected of having the virus. Quarantine and biosecurity procedures have been established and no secondary cases have been reported at this time, on this farm.
These cases have not been confirmed by laboratory testing, but through clinical diagnosis.
"The three British Columbia horses that returned from the Ogden show developed neurological disease and are being treated intensively as if they had nEHV-1," Equine Canada said.
"Strict biosecurity procedures have been put in place to prevent spread of this disease from this farm."
Equine Canada's Health and Welfare Committee said it is believed the initial cases were in horses attending the Ogden event and that horses exposed to the virus at this competition played a role in reported cases elsewhere.