Wisconsin health officials are again warning of the dangers of mosquito-borne diseases after detecting the first West Nile virus activity in the state in 2024.

The Wisconsin Department of Health Services confirmed WNV infections in a healthy blood donor from Washington County in southeastern Wisconsin whose blood screened positive for WNV, and in a dead bird from Chippewa County in the northwest that tested positive for the virus.

The positive blood donor is not considered a human case because they never developed any symptoms of WNV, which is required to be a probable or confirmed case, according to the WDHS.

But the infections confirm the state does have mosquitoes infected with WNV that can transmit the virus to other people and animals.

“The first activity of West Nile virus this year in Wisconsin is a reminder that we still need to take precautions to prevent mosquito bites even as summer winds down, as the risk of West Nile virus continues until the first frost,” State Health Officer Paula Tran said in a news release.

WNV is spread to humans, birds and other animals through the bite of an infected mosquito. Mosquitoes acquire WNV by feeding on infected birds. The virus is not spread directly from person to person, animal to animal or animal to person.

About 80% of people infected with WNV do not have symptoms, so occasionally healthy blood donors may unknowingly donate blood while infected with WNV, according to the WDHS. To prevent spread of WNV through blood transfusions, all donated blood in the U.S. is tested for the virus. Any blood product that tests positive is removed from the blood supply.

DHS has monitored the spread of WNV since 2001. An average of 18 WNV cases are reported among Wisconsin residents each year. WNV cases in humans have been reported from June through October; however, most people with WNV report becoming ill in August and September, according to the DHS.

Those who become ill with WNV usually experience mild symptoms such as fever, headache, muscle ache, rash and fatigue. However, less than 1% of those infected with the virus get seriously ill with symptoms that include high fever, muscle weakness, stiff neck, disorientation, mental confusion, tremors, confusion, paralysis and coma. Older adults and those with compromised immune systems are at greater risk of developing severe illness that can be fatal. It is important people contact a health care provider if they suspect they have WNV illness.

The best way to avoid illnesses spread by mosquitoes is to reduce exposure to mosquitoes and eliminate mosquito breeding sites. Mosquito activity and the risk of WNV will continue until there is a hard frost with temperatures below 28 degrees Fahrenheit for at least four straight hours.

To avoid mosquito bites —

— Apply an insect repellent with DEET, picaridin, oil of lemon eucalyptus or IR3535 to exposed skin and clothing.

— Before heading outdoors, treat clothing with permethrin but do not apply permethrin directly to skin.

— Consider rescheduling outdoor activities that occur during evening or early morning hours, when mosquitoes that spread WNV are most active.

— Wear long sleeves, long pants and socks when outdoors to help keep mosquitoes away from skin.

Mosquito-proof your home —

— Prevent mosquitoes from breeding around the home by removing stagnant water around the property.

— Empty standing water that has collected in tin cans, plastic containers, flower pots, discarded tires, roof gutters and downspouts.

— Turn over wheelbarrows, kiddie pools, buckets and small boats such as canoes and kayaks when not in use.

— Change the water in bird baths and pet dishes at least every three days.

— Clean and chlorinate swimming pools, outdoor saunas and hot tubs; drain water from pool covers.

— Make sure the home’s window and door screens are intact and tightly fitted to prevent mosquitoes from getting inside.

— Trim or mow tall grass, weeds and vines, since mosquitoes use these areas to rest during hot daylight hours.

For more information, go to the DHS websites, https://www.dhs.wisconsin.gov/mosquito/index.htm and https://www.dhs.wisconsin.gov/fight-bite/index.htm.