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

The first trace of the West Nile virus this season was found in Denver through a positive mosquito sample. On Thursday, the Denver Department of Public Health & Environment announced that the virus was found through routine mosquito sample testing.

Macomb County has its first case of West Nile virus in mosquitoes this summer, health officials announced on Thursday. The virus was detected in a single sampling of mosquitoes gathered in Macomb County, officials said. No confirmed human cases of the virus have been reported in Michigan so far.