A batch of mosquitoes sampled July 6 in Mundelein tested positive for the West Nile virus, the first indicator of its presence here, Lake County health officials reported Tuesday.
Residents are cautioned to limit outdoor activity at dusk to avoid exposure, wear insect repellent and report areas of stagnant water where mosquitoes typically breed.
"It's a couple of weeks earlier than we have had in the past but it's not unexpected," said Mike Adam, senior biologist with the health department. "There aren't many mosquitoes out so people fall into a false sense of security."
Most people infected with West Nile have no symptoms but some can become ill usually three to 15 days after the bite of an infected mosquito. In some people, particularly the elderly, the virus can cause muscle weakness, inflammation of the brain or other symptoms and can be potentially fatal.
"The concern is that it's going to increase quickly," Adam said.
In 2011, one bird and 14 mosquito batches tested positive for West Nile in Lake County but there were no human cases and have not been any for several years. Residents with questions should call the West Nile hotline at (847) 377-8300.
In related news, Clarke, a company that serves about 175 communities in the Chicago area, on Tuesday debuted two "earth friendly" mosquito control products in Lincolnshire. Technicians riding bicycles put larvicide in storm drains to kill the Culex mosquito, which carry West Nile.
The products are EPA registered and are listed by the Organic Materials Review Institute, meaning they can be used in and around organic gardens and farms, according to the company. Clarke is demonstrating the products and other measures to reduce its carbon footprint in Lincolnshire, Lake Bluff and Fort Sheridan.
George Balis, entomologist and regional manager with Clarke, said he has seen "a lot of positive samples" of West Nile in mosquitoes particularly in DuPage and Cook counties.
The Culex mosquito breeds in gutters and storm drains, among other areas. It has been "much more viable" this year because of the dry conditions and lack of water movement in breeding areas, he added.