The West Nile virus was discovered in five mosquito traps recently, three in Batavia and two in St. Charles, an entomologist for Clarke Environmental said.
West Nile is a virus carried by the Culex mosquito. Clarke has several traps for mosquitoes set in Batavia, Geneva and St. Charles as part of its spraying contract with the cities.
Clarke entomologist George Balis said testing results are reported to the Illinois Department of public Health.
“Several traps have tested positive,” Balis said. “[There were] two positives in Batavia on July 31 from two different samples and a third on Aug. 14 from the same area. In St. Charles, [there were] two positives, on Aug. 7 and Aug. 14, from two separate areas.”
No mosquitoes tested positive in Geneva, he said.
The Illinois Department of Public Health confirmed the first human West Nile virus case reported in Illinois was a Chicago woman in her 70s who became ill in July.
The West Nile virus is transmitted through the bite of a mosquito that has picked up the virus by feeding on an infected bird. Common West Nile virus symptoms include fever, nausea, headache and muscle aches. Most people who are bitten have no symptoms, but others can develop severe illness, according to the health department.
Balis said the company does not reveal trap locations where mosquitoes tested positive for West Nile because residents might believe their risk is lower if they live some distance away.
“The positive tests show a presence of the virus in the region,” Balis said. “West Nile virus is endemic. It’s found within the region year after year during periods we see now.”
The Culex mosquito comes from stagnant water near houses and also is known as the northern house mosquito.
In addition to Clarke spraying for mosquitoes, cities and villages have their own treatments of storm drains to reduce mosquito breeding areas, Balis said.
According to the state health department, Culex pippins and quinquefasciatus are the two species of house mosquitoes that carry West Nile virus.
Culex will lay rafts of eggs on still water – they cannot develop in running water – so ridding areas of stagnant water is key to reducing the incidence of West Nile. Culex also will not travel far from where they breed, so health officials urge residents to clean out bird baths, flower pots, clogged gutters and buckets, according to the health department website.
The Aedes group of mosquito species – also known as a nuisance or floodwater mosquitoes – will lay eggs on the ground, which hatch after a heavy rain. Flood mosquitoes can fly up to 10 miles away from where they were bred, according to the health department website.
Balis said he had a case in Huntley where a woman was besieged with mosquitoes, and Clarke found 25 areas in her yard in which Culex was breeding.
“She had a bucket full of water. She had corrugated piping from her downspouts – all four of them breeding mosquitoes,” Balis said. “She had a bird bath and a wheelbarrow. It was full of weeds that she had been picking, but it had 2 to 3 inches of rain below the weeds. She had a recycling bin clogged at the bottom and trees growing out of her gutters.”