The Wisconsin Department of Health Services (DHS) announces the first West Nile virus (WNV) infections in Wisconsin this year in a healthy blood donor from Washington County, whose blood screened positive for WNV, and in a dead bird from Chippewa County 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. The infections confirm that there are mosquitoes infected with WNV in the state 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. While West Nile virus and other viruses spread by mosquitoes pose a risk to all Wisconsinites, people who have weakened immune systems are at higher risk for significant illness," said State Health Officer Paula Tran.

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.

Most people (80%) who are infected with WNV do not have symptoms, so occasionally healthy blood donors may unknowingly donate blood while infected with WNV. 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 cases of WNV illness 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.

Those who become ill with WNV usually experience mild symptoms such as fever, headache, muscle ache, rash, and fatigue. However, some people (less than 1%) who become 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 through the rest of the summer until there is a hard frost (temperatures below 28 degrees Fahrenheit for at least four straight hours). DHS offers these tips to protect yourself and your family against mosquito bites:

Avoid Mosquito Bites

• Apply an insect repellent with DEET, picaridin, oil of lemon eucalyptus, or IR3535 to exposed skin and clothing.
• Prior to heading outdoors, treat clothing with permethrin; 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 your skin.

Mosquito-Proof Your Home

• Prevent mosquitoes from breeding around your home by removing stagnant water from items around your 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 window and door screens are intact and tightly-fitted to prevent mosquitoes from getting into your home.
• Trim or mow tall grass, weeds, and vines since mosquitoes use these areas to rest during hot daylight hours.

Find more information on illnesses spread by mosquitoes and additional ways to Fight The Bite on the DHS website.