WASHINGTON -- Health officials said Friday that three more people have died from West Nile virus this week as the disease continues its most deadly rampage yet in the United States.

The Illinois Department of Health reported that two Chicago-area women in their 80s died Friday of the virus, bringing to seven the number of fatalities in the state this year -- the most of any state.

The Midwestern State also reported 24 new cases of West Nile, bringing its total to 122 cases.

In Maryland, health officials said an 87-year-old woman in the Washington suburb of Bethesda, Maryland, died Tuesday from encephalitis brought on by the virus.

"She has tested positive for West Nile virus," although the results have not been confirmed, said John Hanson, a spokesman for Maryland's Department of Health and Mental Hygiene.

If federal health officials confirm the three women died from West Nile, it would bring to 31 the number of deaths this year in the United States from the virus. At least 555 people have been infected, according to the Atlanta, Georgia-based Centers for Disease Control and Prevention.

The virus, first isolated in the West Nile district of Uganda in 1937, emerged in parts of Europe in recent years and first appeared in New York in 1999. It has since been spreading across the United States.

Meanwhile, health officials in Ontario, Canada said three Canadians were probably infected with the disease, which would be the first human cases documented in Canada.

Preliminary tests led specialists to suspect West Nile virus in the case of two Ontario men, while a third person is believed to have contracted the disease while on a visit to the United States.

While authorities wait for the results of further tests, one of the two men -- who is in his 60s -- has been listed in serious condition in the hospital, Ontario Chief Medical Officer Colin d'Cunha said. The second patient has been discharged.

Healthy people who contract West Nile virus suffer a mild flu-like illness and can avoid any long-term effects with treatment.

However, in about one in every 150 cases, the virus can cause encephalitis, which can be fatal among the elderly or infirm -- and especially among those with compromised immune systems.