Toronto Public Health say they have received two reports of probable human cases of West Nile virus in the city.

If confirmed, they would be the first human cases so far this year.

Dr. Howard Shapiro, the associate medical officer of health in Toronto, said Thursday that the cases involve an 80-year-old man in hospital and a 32-year-old woman recovering at home.

West Nile was first discovered in Toronto in 2001, and in 2002 there were 163 cases and 11 deaths. But there have been no deaths in Toronto from West Nile since 2005. Before Thursday's announcement, there had only been one case since 2010.

Shapiro told CBC News earlier this week that the number of mosquitoes found to have West Nile virus is at a record high this summer, likely due to the warm weather.

West Nile thrives in hot weather

Hotter weather is associated with higher viral loads in mosquitoes, which pick up the virus from birds they bite and then spread it to people.

Only about one in five infected people get sick. One in 150 infected people will develop severe symptoms including neck stiffness, disorientation, coma and paralysis.

The best way to prevent West Nile disease is to avoid mosquito bites. Insect repellents, screens on doors and windows and wearing long sleeves and pants are some of the recommended strategies. Experts also suggest emptying standing water from buckets, kiddie pools and other places to discourage mosquito breeding.

There have also been two human cases confirmed recently in Winnipeg and one in Windsor, Ont. All of the cases were mild and were discovered by Canadian Blood Services after blood donations.

In the U.S., more serious illnesses from West Nile virus have been reported so far this year than any since 2004.

Through the end of July, 241 human cases have been reported in 22 states, including four deaths. Texas, especially around the Dallas area, has seen the bulk of them.