With the first reports this year of West Nile virus in Wisconsin coming out this week, health experts are warning the first human cases may not be far behind.
On Monday, Wisconsin DHS announced that a dead bird from Chippewa County and the blood screening of a blood donor from Washington County had both tested positive for West Nile.
These positive tests confirm mosquitoes in Wisconsin are carrying the West Nile virus, according to DHS. The reports come after mosquito season is in full swing in Wisconsin amid a rainy, humid summer.
Here’s what to know about West Nile virus in Wisconsin and how to best protect yourself.
What is West Nile Virus?
West Nile virus is the leading mosquito-borne illness in the U.S. and usually spreads during the peak mosquito season, which is from summer to early fall.
Mosquitos pick up the virus from infected birds, and humans can contract the virus if bitten by an infected mosquito. Humans cannot pass the virus to each other, except in a few rare cases: through blood transfusions or organ transplants if the donor is infected, and from mother to baby during pregnancy, delivery or breastfeeding.
Symptoms of West Nile virus
About 80% of people who contact West Nile will not develop any symptoms, according to the Centers for Disease Control and Prevention.
The remaining 20%, or about one in five people, may develop symptoms including a fever, headache, body aches, joint pains, vomiting, diarrhea or rash. Most people with symptoms will recover completely, but general fatigue and weakness can last for a few weeks or even months.
About 1 in 150 infected people develop more severe illness that debilitates the central nervous system. Severe symptoms include high fever, neck stiffness, disorientation, convulsions, vision loss and paralysis. People older than 60 or people with pre-existing medical conditions — like cancer, diabetes, kidney disease and hypertension — are at greater risk of developing serious infections.
Are there any West Nile cases in Wisconsin?
Though a blood sample tested positive for the virus, DHS said the donor did not exhibit any West Nile symptoms, so the positive activity is not considered a case. As of Aug. 6, there are no human cases of West Nile in Wisconsin.
In 2023, Wisconsin saw 25 confirmed and probable cases of the virus — up from the annual average of 16 cases annually since 2014, according to DHS.
So far this year, 26 states have reported human cases, according to the CDC. As of Aug. 6, the nationwide case count has totaled 103 infections, with 68 of them being more severe, neuro-invasive cases.
Texas is seeing the worst outbreak with 18 cases so far. Michigan, Minnesota and Illinois, which all border Wisconsin, have each reported one human case.
Is West Nile virus preventable?
There are no vaccines to prevent West Nile virus, but you can avoid contracting the virus by taking steps to prevent mosquito bites. Here are a few simple, low-cost ways to protect yourself from mosquitoes:
- Avoid mosquito breeding sites. A map of the sites can be found on the DHS website.
- Avoid having standing water around your home. Buckets of water should be emptied out and bird bath water should be kept clean to avoid creating spaces for mosquitoes to lay eggs.
- Use insect repellent. Products with DEET, a key ingredient in many repellents, will be especially effective; but if you’re looking for a plant-based option, repellents with lemon eucalyptus are also proven to work.
- Wear long sleeves and pants outside, especially during peak mosquito hours around sunset.
- If you’re sitting outside, use an outdoor fan to disturb and deter mosquitoes’ flight.
Jolan Kruse contributed to this report.
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