ST. PAUL, Minn. (CBS-KFGO) – The Metropolitan Mosquito Control District said Thursday that it found mosquitoes in Minnesota’s Anoka and Carver counties with West Nile virus. “The mosquito-borne disease risk tends to elevate as we get late into the summer,” said the district’s Alex Carlson.

Most West Nile cases in Colorado happen between July and September, though mosquitoes can live until the first snow or hard freeze.

West Nile Virus was first reported in the U.S. in 1999. The virus spreads through mosquito bites, although most people who catch it won’t experience symptoms. About 20% of those infected will develop symptoms such as fever. Less than 1% of those infected will develop a more severe and sometimes fatal illness.