TORONTO -- Ontario's chief medical officer of health says three people have contracted a virus linked to exposure to rats.

Dr. David Williams says the Ministry of Health and Long-Term Care is investigating three human cases of Seoul virus among people who had prolonged contact with rats. Williams says no serious health problems have been reported.

Seoul virus is a type of hantavirus that can be transmitted from rats to people through bite wounds or exposure to urine, feces, saliva or contaminated bedding.

Officials say the health risk to Ontarians is considered low and Seoul virus is not spread from person to person.

A person infected with Seoul virus may not develop symptoms or will only develop very mild symptoms. However, in some instances, more severe symptoms may include fever, severe headache, back and abdominal pain, chills, blurred vision, redness of the eyes, or rash.

Williams says the source of the illnesses, including links to a multi-state investigation in the U.S., is being investigated.

As of Feb. 24, the Center for Disease Control and Prevention is investigating a similar Seoul virus outbreak associated with rat exposure that involves 16 positive human cases and rat breeders located in 15 states.

Rats do not show symptoms of disease when they are infected with Seoul virus.