Mosquitoes collected in Sandwich city limits have tested positive for West Nile virus, according to a Thursday DeKalb County Health Department announcement.

So far this year, mosquito traps have identified West Nile virus present in Genoa, DeKalb and Sycamore health officials said.

No known human cases have been reported in DeKalb or Kendall counties so far in 2025, according to the health departments. The Kendall County Health Department reported its first positive mosquito trap sample with West Nile virus on July 24. As of Aug. 25, the Illinois Public Health Department has reported 11 cases of the virus in humans, with no fatalities this year so far.

The virus can be transmitted through the bite of an infected mosquito. The bugs usually become infected by feeding on an infected bird. Health officials said it’s important to remember that most mosquitoes and birds do not carry West Nile virus, though the public still should be aware of its risks.

West Nile virus usually results in mild symptoms but also can cause serious illness. About 20% of people who become infected with the virus develop a fever and other symptoms, while about 1 out of 150 infected people develop a serious, sometimes fatal illness, according to the U.S. Centers for Disease Control and Prevention.

While DeKalb County health officials report that most people infected with West Nile virus have no clinical symptoms, those who do will become ill between three and 14 days after being bitten by an infected mosquito.

Mild cases of West Nile virus can include fever, headache and body aches. More serious cases can cause encephalitis and meningitis to develop, health officials said.

There are no West Nile virus vaccines that are licensed for use in humans, according to the CDC. Although local officials said most mosquitoes don’t carry West Nile virus, they also said the most effective way to prevent a viral infection is to reduce the chances of being bitten by mosquitoes.

Tips to stay healthy and safe

• Avoid being outdoors when mosquitoes are most active, especially between dusk and dawn.
• When outdoors, wear shoes and socks, long pants and a long-sleeved shirt, and apply insect repellent that includes DEET, picaridin or oil of lemon eucalyptus according to label instructions. Consult a physician before using repellents on infants.
• Make sure doors and windows have tight-fitting screens. Repair or replace screens that have tears or other openings. Try to keep doors and windows shut, especially at night.
• Change water in birdbaths weekly. Properly maintain wading pools and stock ornamental ponds with fish. Turn over any buckets, garbage cans or other containers that collect water.

For more information, visit the DeKalb County Health Department website at health.dekalbcounty.org