So far in 2012, city officials have found more mosquitoes infected with the West Nile virus than any other year in the past decade.

While there have been no confirmed human cases, 24 batches of mosquitoes have tested positive since January. That is four times as many as at this point last year.

Dr Howard Shapiro with Toronto Public Health blames the weather. He says while the number of mosquitoes is at the same level, the heat is driving the multiplication of the virus.

He says people should reduce the risk of being infected by wearing mosquito repellant and covering up between dusk and dawn.

The city has expanded its West Nile prevention program to respond to the higher numbers of infections. The program includes "larviciding," which consists of dropping pesticide into catch basins to control the mosquito population.