Medical Officer of Health Dr. Allen Heimann says test results from mosquitoes in Windsor came back positive, the first sign of the virus in the area this year.
Heimann says although there have been no human cases this year, the positive test results are not surprising because the Windsor area has had West Nile since 2003.
Public health officials in Toronto and St. Catharines said Tuesday they received laboratory reports indicating that mosquitoes have tested positive for West Nile.
Halton Region Public Health last week reported finding West Nile in two mosquito ponds — in Oakville and Milton.
Ontario reported more than 60 human cases of West Nile in 2011.