A batch of mosquitoes tested positive for the West Niles virus in Deerfield on July 8, marking the first positive test of the season in Lake County.
“Hot weather typically increases mosquito activity,” said Tony Beltran, executive director of the county health department. “You can protect yourself against mosquito bites by following the three R’s: reduce your exposure to mosquitoes, repel them by wearing insect repellent, and report areas where mosquitoes typically breed.”
According to the health department, the number of West Nile cases in humans has remained relatively small since large outbreaks in 2002, 2005 and 2006.
Last year in Lake County, 41 mosquito pools tested positive for the virus, there were five human cases and two in birds, officials said.
West Nile can result in headaches and fever. In some individuals, particularly the elderly, the virus can cause muscle weakness, inflammation of the brain (encephalitis), stiff neck, stupor, disorientation, tremors, convulsions, paralysis, coma or death, according to the Lake County Health Department.
Symptoms occur three to 15 days after a bite from an infected mosquito. Those at the greatest risk for serious illness are those 50 years of age or older. The infection risk is highest in late summer, officials said.
The virus was first identified in Illinois in September 2001 after it first showed up in New York in 1999. In 2002, there were 884 human cases and 64 deaths in Illinois. There were eight cases and one death in 2002 in Lake County.
In 2003, there was only one human case and there were zero in 2004, officials said. In 2005 and 2006, the county reported 11 human cases each year, and one death in 2005. Over the next five years, there were only five total cases. In 2012, however, there were seven cases and five cases in 2013.
In total, there have been 48 human cases and two deaths in Lake County.
The common house mosquito, Culex pipiens, is the main carrier with 70 percent of the positive samples coming from this mosquito or related species of Culex, which need stagnant water with lots of organic material, according to the Illinois Department of Public Health. Flood mosquitoes are minor carriers, according to the state health department.
The county health department conducts a multi-faceted mosquito surveillance program, monitoring dead crows, robins, blue jays, mosquitoes and horses. Mosquitoes can either carry the virus or get it by feeding on infected birds.
Beginning in late spring and into the autumn, a series of traps are set around the county, including within the Lake County Forest Preserves. At each site, a pool or batch of mosquitoes is tested weekly for West Nile virus.
For more information from the county, visit http://health.lakecountyil.gov/Population/Pages/West-Nile-Virus.aspx.