Public health staff outline West Nile virus surveillance, urge larval control and precautions

Public health officials told the Kane County Public Health Committee on Sept. 17 that West Nile virus is seasonal in the county and that prevention focuses on reducing mosquito breeding sites, personal protection and targeted larval control.

Why it matters: West Nile virus is an arboviral disease typically transmitted to people by infected Culex mosquitoes; though most infections are asymptomatic, a small share can develop severe neuroinvasive illness, particularly in late summer and early fall.

April Elliott, assistant director for communicable disease, said West Nile is a reportable disease under the Illinois Administrative Code for Notifiable Diseases and Conditions (section 690.322 for arboviral infections) and described local trends: from 2015–2024 the county has periodically detected positive mosquitoes, birds and human cases. “From 2015 to 2024 we typically see human onsets predominantly in August and September,” she said.

Elliott noted that most infected people have no symptoms; about one in five develop a flu-like illness, and a substantially smaller share develop severe neuroinvasive disease. She said incubation is typically two to six days but can be as long as three weeks.

Kristen Johnson, environmental health supervisor, described the county’s mosquito program: identifying and eliminating breeding sites, responding to community complaints, trapping and testing mosquitoes, larval dipping, public education and targeted larviciding. Johnson said the Culex pipiens species (the house mosquito) is the principal vector for West Nile virus locally and tends to breed in water-holding containers, gutters and abandoned pools with a short flight range of one to two miles; the nuisance floodwater species (Aedes vexans) can fly farther and bites more aggressively.

Johnson described trap types used by the county (including a fan-based trap that collects mosquitoes seeking egg-laying sites) and the use of rapid testing platforms for pools of mosquitoes. She said the county temporarily suspended dead-bird collection this season because of concerns about highly pathogenic avian influenza H5N1 and advised residents not to handle dead birds.

Speakers emphasized larvicide (pellets or briquettes applied to stagnant water) as the most targeted and environmentally protective control; municipal or commercial adulticiding (fogging) is less effective and has greater environmental side effects, the presenters said. Johnson added that applicators must hold a Department of Agriculture larvicide applicator license.

Committee members asked about community outreach and materials; staff said the county posts information on its website, shares door-hanger handouts at health fairs and coordinates with the Illinois Department of Public Health and municipal partners.

The presentation was informational; staff did not request or record a formal policy decision at the meeting. Officials said they will send the committee the slide deck and related materials and continue routine surveillance and community outreach.

(Reporting note: scientific names of mosquito species and the state code citation are reported as described by staff; technical spellings have been standardized to scientific usage: Aedes vexans and Culex pipiens.)