Restricted access and additional biosecurity protocols remain in place at the Equine Research Park and the Annex, in response to a confirmed case of EHV-1.
The quarantine at the Research Park and the Annex will be in place for an additional week, a spokesperson said.
"Presently, there are no horses exhibiting symptoms of EHV-1. While we believe there is a low risk of exposure, we are taking every precaution to ensure the health and well-being of all animals."
The EHV-1 cases have not affected the Companion Animal or Farm Animal Hospital.
These hospitals remain open and operating under normal conditions, as EHV does not affect dogs, cats, cattle, sheep, goats, pigs, or birds.
The quarantine was put in place in late March after two confirmed cases of the virus.
One involved a day-old foal admitted to the equine hospital on March 18. It died two days later of pneumonia, and tests confirmed EHV-1 on March 25.
During the same time a gelding was being treated for a spinal injury.
He left on March 22, but became severely ill on return home and subsequently tested positive for EHV-1 on March 30. The gelding is now recovering.