A batch of mosquitoes sampled July 8 in Deerfield is the first confirmed indicator of the West Nile virus this season in Lake County, officials said Wednesday.
The first detection was earlier than the average July 14 date the past 10 years, but there is no way to tell how the rest of the season will fare, said Mike Adam, senior biologist for the Lake County Health Department. Last year, 41 batches tested positive.
Cool, wet weather is not conducive for the Culex mosquitoes that are the primary carrier of West Nile, Adam said. Hot and dry weather can "amplify" the virus through the mosquito population, he added, but the current pattern likely will delay that process.
"We don't want to put our guard down yet. Things can turn around quickly," Adam said.
Most people infected by the bite of a mosquito have no symptoms of illness. But in some people, particularly the elderly, the virus can cause muscle weakness, stiff neck, encephalitis, paralysis, coma or death.
Last year in Lake County, five human cases and two bird cases were confirmed. No bird cases have been detected this year.
"There are a couple of things we look for, but the driver is the weather," Adam said.
The wet weather has been flushing catch basins of mosquitoes that could carry West Nile, but has increased the number of floodwater or nuisance mosquitoes.
Adam said about 30 or so traps primarily targeting the Culex mosquito are placed throughout the county and forest preserves, and are tested once a week. The health department conducts mosquito surveillance from late spring until fall that includes monitoring the location of dead birds to help assess the threat of potential West Nile activity and investigating areas of stagnant water, which are potential breeding areas for mosquito larvae.
Health officials say everyone should enjoy the outdoors but protect themselves against mosquito bites by following the "three Rs" -- reducing exposure; using insect repellent; and, reporting areas where mosquitoes typically breed.
Repellent should include DEET, picaridin, oil or lemon eucalyptus or IR3535, and activity should be limited at dusk.
Old tires, buckets, drums or other water-holding containers that can become breeding areas should be discarded. Plastic wading pools should be emptied at least once a week and stored indoors. Unused swimming pools should be drained.
To report areas of stagnant water or to learn more West Nile, call the health department hotline (847) 377-8300 or visit http://health.lakecountyil.gov/population/pages/west-nile-virus. aspx.