First 2024 Human Case of West Nile Virus in Illinois

The Illinois Department of Public Health (IDPH) announced the first human case of 2024 in Illinois of West Nile virus (WNV), the mosquito-borne illness. While commercial testing and clinical symptoms indicate a case of WNV, IDPH routinely sends the first positive case to CDC for confirmatory testing, which is pending. The individual is in their 60’s and lives in suburban Cook County. The onset of WNV symptoms was in mid-June.

IDPH is tracking positive batches of birds and mosquitos on its West Nile virus dashboard and has reported 33 Illinois counties this year with positive results, an early warning of the presence of WNV in an area.

“Summer in Illinois means mosquitos, and these mosquitos increase our risk of contracting vector-borne illnesses like West Nile Virus,” said IDPH Director Dr. Sameer Vohra. “We encourage all Illinois residents to ‘Fight the Bite’ and protect themselves and their loves ones from insect bites that can cause potentially serious illnesses."

There were 119 human cases of WNV reported in Illinois in 2023, up from 34 human cases in 2022. There were six human deaths attributed to West Nile virus in the state in 2023, compared to seven in 2022. The first 2023 human case in Illinois occurred in late June.

IDPH supports mosquito control efforts throughout the state by providing a total of $2.8 million in funding to the 97 local health departments in Illinois for vector surveillance and control activities. This includes purchasing and applying larvicide, working with local municipal governments and local news media for WNV prevention and education, and investigating mosquito production sites and nuisance mosquito complaints. Local health departments collect mosquitoes for West Nile virus testing and also collect sick or dead birds for West Nile virus testing.

West Nile virus is transmitted through the bite of a Culex mosquito, commonly called a typical mosquito, which has picked up the virus by feeding on an infected bird. Common symptoms of WNV include fever, nausea, headache and muscle aches. Symptoms may last from a few days to a few weeks. Four out of five people infected with West Nile virus will not show any symptoms. However, in rare cases, severe illness can occur, including brain infections such as meningitis or encephalitis and paralysis or even death. People older than 50 and immunocompromised individuals are at higher risk for severe illness from West Nile virus.

There is no specific treatment for WNV nor is there a vaccine at present, therefore it is critically important that people minimize their risk of acquiring.

IDPH encourages the public to Fight the Bite and take steps to prevent WNV by practicing the three “R’s” – reduce, repel, and report:

• REDUCE - make sure doors and windows have tight-fitting screens.  Repair or replace screens that have tears or other openings.  Try to keep doors and windows shut.
  Eliminate, or refresh each week, all sources of standing water where mosquitoes can breed, including water in bird baths, ponds, flowerpots, wading pools, old tires, and any other containers.
• REPEL - when outdoors, wear shoes and socks, long pants and a light-colored, long-sleeved shirt, and apply an EPA-registered insect repellent that contains DEET, picaridin, oil of lemon eucalyptus, or IR 3535 according to label instructions. The CDC does not recommend use of products containing oil of lemon eucalyptus or para-menthane-diol on children under 3 years old. Consult a physician before using repellents on children under 3.
• REPORT – report locations where you see water sitting stagnant for more than a week such as roadside ditches, flooded yards, and similar locations that may produce mosquitoes.  The local health department or city government may be able to add larvicide to the water, which will kill any mosquito larvae.

Surveillance for West Nile virus in Illinois involves reporting and investigation of individuals with West Nile virus symptoms and clinical laboratory testing. Environmental surveillance includes laboratory testing on mosquito batches, dead birds, as well as testing sick horses. People who observe a sick or dying bird should contact their local health department, which can determine if the bird will be picked up for testing.