MONTREAL -- An Ontario woman is the first person in Canada to have contracted the West Nile virus through a blood transfusion, health officials confirmed Friday.

The virus was found in blood samples from a 57-year-old woman from Kitchener, who succumbed to encephalitis.

In about one case in 150, the virus causes encephalitis, which in its most severe form can be fatal.

"The source of this infection is most likely a blood transfusion," AFP quoted a regional health official as saying.

Two Canadians have been confirmed to have died from the virus, which was first isolated in the West Nile district of Uganda in 1937.

Some 103 people nationwide have "probable" cases of the usually mosquito-borne disease and 73 others have "confirmed" cases of West Nile virus, according to records from the three provinces reporting human cases.

The United States, where the virus first appeared in 1999, has had 146 deaths from the disease, according to the Centers for Disease Control and Prevention in Atlanta, Georgia.

U.S. officials said in August that the virus can be transmitted through blood transfusions.