Electron micrograph of EHV-1.
The Canadian Food Inspection Agency (CFIA) said EHV is not a federally controlled disease, and that it had no authority to request certification related to the disease from the United States Department of Agriculture when importing horses from the US.
"Import conditions for all horses entering Canada from the US will not be changed in relation to the recent reports of EHV cases in the US.
"However, as always, imported horses need to comply with all current Canadian import conditions. In addition, arrival of unwell horses at the border can affect the import process."
Evidence suggests the potentially deadly infection spread from horses who were at the National Cutting Horse Association's Western National Championship in Ogden, Utah, from April 30 to May 8.
The Utah Agriculture Department said that, as of 6pm on Tuesday, preliminary laboratory results of nasal swab samples of suspect cases found in the state had tested negative for the virus.
Oregon agriculture authorities said they had alerted veterinarians around the state to monitor for signs of the disease, but there had been none to date.
The most common way for EHV-1 to spread is by direct horse-to-horse contact. The virus can also spread through the air, contaminated equipment, clothing, and hands.
Symptoms include fever, decreased coordination, nasal discharge, urine dribbling, loss of tail tone, hind limb weakness, leaning against a wall or fence to maintain balance, lethargy, and the inability to rise. While there is no cure, the symptoms of the disease may be treatable.