CHICAGO (CBS) — For the first time this year, public health officials have detected West Nile virus in mosquitos in north suburban Lake County.

Lake County Health Department officials said a batch of mosquitos trapped on June 28 in Highland Park has tested positive for the disease.

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West Nile virus can be passed on to humans when they are bitten by an infected mosquito.

Most people who are infected with West Nile show no symptoms of the disease, but it can cause fever, nausea, headaches, and muscle aches. Most people who get sick begin showing symptoms 3 to 15 days after a mosquito bite.

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In rare cases, the virus can cause severe illness, including meningitis or encephalitis, which are potentially deadly inflammations of brain or spinal cord tissue. People older than 50 or with weakened immune systems are at greatest risk of a severe illness.

Last year, there were six human cases of West Nile confirmed in Lake County. Since 2002, there have been 64 confirmed human cases of the disease in Lake County, including to deaths.

Health officials say the best defenses against West Nile virus are using insect repellent containing DEET when outdoors, draining any standing water that can serve as a breeding ground for mosquitos (even small puddles or bottle caps), limiting outdoor activity at dawn and dusk when mosquitos are most active, and covering as much skin as possible with light-colored clothing.

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For more tips on preventing mosquito bites, click here.