At least one person has died from West Nile virus in Michigan.
The state health department says there have been eight human cases so far this year, including five in Wayne County.
Michigan's chief medical executive, Dr. Eden Wells, says West Nile is a threat until the weather cools off. The virus is passed through bites from infected mosquitoes.
Older people are vulnerable, especially if they have other health problems. Most people who become infected will not develop any symptoms, but some become sick three to 15 days after exposure.
