Michael Slamecka, a biologist with the South Cook County Mosquito Abatement District, fogs areas in Chicago Heights in this June 2018 file photo, trying to kill off adult mosquitoes and their larvae. (John Smierciak / Daily Southtown)

Mosquitoes carrying the West Nile virus have been found in areas in Will and Cook counties as experts urge residents to remove stagnant water from their yards and take protective measures when outdoors at night.

This week, the Will County Health Department confirmed its first West Nile virus positive mosquito sample of the season in a trap in Homer Glen, department spokesman Steve Brandy said.

The South Cook County Mosquito Abatement District reported mosquitoes carrying the West Nile virus in Orland Park, South Holland and Evergreen Park about a week ago, and new positive samples in Chicago’s Mount Greenwood community on Wednesday, said Janet Rogers, operations superintendent of the abatement district.

West Nile virus is transmitted through the bite of a culex mosquito that has picked up the virus by feeding on an infected bird. The Will County Health Department reports symptoms of West Nile include fever, nausea, headache and muscle aches that can last a few days to a few weeks.

“West Nile virus can be very dangerous especially in older people or those with compromised immune systems,” Brandy said.

Extreme heat and standing water helps the culex mosquito multiply, and the first positive samples could be an indicator that there’s more to come, Brandy said.

A very rainy June helped contribute to a surge in the mosquito population, experts said.

The South Cook County Mosquito Abatement District recorded 20 inches of rainfall in Chicago Heights during 10 days in late June, Rogers said. With standing water comes breeding grounds, she said.

Municipalities try to help control the mosquito population through a multifaceted approach of larvicides and spraying the adult population, but also urge residents to take step on their own property to prevent mosquitoes from multiplying.

Brian Williams, public works director for New Lenox, said the village puts tablets designed to kill mosquito larvae in places such as retention basins, ponds or ditches that are often wet. The tablets last a few months. Once mosquito season begins, it follows Will County’s trap counts. If there are 100 female mosquitoes, it is considered a nuisance, and the town sprays to fumigate the adult mosquitoes, Williams said.

“We strictly go by the science,” Williams said.

The spray, which is often started about 8 p.m. and lasts until about 11 p.m. when mosquitoes are most active, can kill the mosquitoes while they are in the air, Williams said.

The products are safe for humans and pets, but the village has a call list to notify residents who may have health concerns.

In Frankfort, there were three villagewide sprays to kill mosquitoes in July, village administrator Rob Piscia said.

The mosquito traps help monitor the larvae to determine how often is necessary to spray.

“We are very proactive in mosquito abatement,” Piscia said. “Thankfully (West Nile virus) is not widespread, but when you have higher concentration of mosquitoes, the chance of getting bit is up and mosquito-borne illnesses go up. That is why we are proactive.”

Mosquitoes can go from eggs to adults in about four days during perfect conditions, which include 80-degree temperatures with 80% humidity, said Jack Thennisch, control consultant for Clarke, a mosquito abatement firm many municipalities use.

In mid-to-late June, the area experienced more rainfall than it had for the first six months of the year, leading to the rise of mosquitoes, Thennisch said.

The company first tries to kill mosquitoes before they hatch, and then concentrates on killing the adult mosquitoes by spraying. Fogging the mosquitoes is about 86% effective, killing them while they are in the air, Thennisch said.

In Homer Glen, where West Nile has been found, Clarke has sprayed twice this summer, he said.

To be effective, the spray droplets need to make contact with flying mosquitoes so the fine mist is released when the mosquitoes are most active. According to Clarke, they work only at the time of treatment to quickly reduce adult mosquito populations. Once applied, it begins to dissipate about 30 minutes later, depending on weather conditions.

Rogers, of the South Cook County Mosquito Abatement District, said spraying to kill mosquitoes is a “temporary fix.” While it is one tool, it isn’t necessarily the most effective.

Rather, the abatement district advocates treating the sources of mosquito breeding grounds, she said.

Boats, tires, bird baths, gutters, kiddie pools and swimming pools that aren’t maintained are some of mosquitoes’ favorite places to breed, Rogers said. Residents need to be vigilant to make sure they aren’t harboring mosquito larvae, and workers with the abatement district can help residents find the water source where mosquito populations thrive, she said.

Mike Slamecka, a biologist with the South Cook County Mosquito Abatement District, said spraying can be effective depending on the right temperature and wind speed, but more mosquitoes replace the ones that have been killed.

Killing larvae is a better approach, he said.

August is generally a wet month, so residents still need to be on the lookout for mosquito breeding grounds and take precautions when going outdoors.

Among the precautions residents can take is wearing long sleeves, pants, socks and shoes and insect repellent with DEET during peak mosquito periods between dusk and dawn, Brandy said.

Will County also operates a West Nile virus hotline where residents can call 815-740-7631, or email westnile@willcountyhealth.org if they find a dead bird.

Michelle Mullins is a freelance reporter for the Daily Southtown.