The Perth District Health Unit says mosquitoes found in Listowel have tested positive for the West Nile Virus.
Officials say the conditions are ideal for mosquito breeding and virus growth.
Four other positive mosquito pools have been found in Ontario and a bird was found to be carrying the virus in Sarnia earlier this summer.
It's expected more mosquitoes and birds carrying the West Nile Virus will be found in other jurisdictions before the end of summer.
As a result catch basins will be treated for mosquito larvae throughout the rest of the year in Perth County and mosquito trapping will continue as well.
Four out of five people bitten by an infected mosquito don't show any symptoms. But those over 50 and with compromised immune systems are at higher risk.
