The City of Hamilton is moving the risk of West Nile virus from low to moderate after confirming the first human case this year.
Most people infected with West Nile will have no symptoms but about 20 per cent, including older adults or people with weakened immune symptoms, could experience West Nile fever.
If symptoms do occur, they appear two to 14 days after being bitten by an infected mosquito.
Residents are being reminded to protect themselves against bites by using a mosquito repellent and wearing light-coloured, long sleeves shirts and pants when in wooded areas or in the garden.
Standing water should be removed at least weekly to to prevent breeding.
Hamilton has begun its first round of larviciding treatments on city street catch basins.