West Nile Virus

2021 West Nile Virus Activity (as of September 10, 2021)

*National mosquito pool and bird data are not reported

2021 West Nile Virus Activity Data provided through the Michigan Department of Health and Human Services (MDHHS) MI Disease Mapper, the MDHHS Arbovirus Activity Daily Outbreak Summary, and the Centers for Disease Control and Prevention.

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What is West Nile Virus (WNV)?

West Nile Virus (WNV) is a potentially serious illness. Experts believe it is established as a seasonal epidemic in North America that flares up in the summer and continues into the fall. It can infect humans, birds, horses and some other mammals. In a small number of people infected by the virus, the disease can be serious, even fatal.

How is WNV spread?

  • WNV is most often spread to humans by the bite of an infected mosquito that gets infected by biting a bird that carries the virus. Horses and other mammals bitten by mosquitoes that carry the virus can also become infected. Whenever mosquitoes are active, there is a risk of getting WNV. The risk is highest from late July through September.
  • In a very small number of cases, WNV has been spread through blood transfusions, organ transplants, breastfeeding and during pregnancy from mother to baby.
  • WNV is not spread through casual contact such as touching or kissing a person with the virus.

What are the symptoms of West Nile Virus?

If symptoms develop, they usually appear 3 to 14 days after the bite of an infected mosquito.

  • Serious Symptoms in a Few People. About one in 150 people infected with WNV will develop severe illness. Symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent.
  • Milder Symptoms in Some People. Up to 20% of the people who become infected display symptoms such as fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days; though, even healthy people have been sick for several weeks.
  • No Symptoms in Most People. Most people (80%) infected with WNV do not have any symptoms.

What is the treatment for WNV?

There is no treatment for WNV infection. Illness may last weeks to months, even in healthy persons. In more severe cases people may need hospital care for supportive treatment such as intravenous fluids, help with breathing, or nursing care.

What should I do if I think I have WNV?

Milder WNV illness usually improves without medical attention. A person may choose to see their doctor. Seek medical attention immediately if symptoms of severe WNV illness develop, such as unusually severe headaches or confusion. Severe WNV illness usually requires hospitalization. Pregnant women and nursing mothers who develop symptoms that could be WNV are encouraged to see their doctor.

What is the risk of getting sick from WNV?

  • People over 50 years of age at higher risk of severe illness. People over the age of 50 are more likely to develop serious symptoms of WNV if they do get sick and need to take special care to avoid mosquito bites.
  • Being outside means you're at risk. Avoid mosquito bites when outside working, playing or relaxing.
  • Risk of infection through medical procedures is very low. All donated blood is checked for WNV before being used. The risk of getting WNV through blood transfusions and organ transplants is very small, and should not prevent people from having surgery. If you have concerns, talk with your doctor.
  • Pregnancy and nursing do not increase the risk of becoming infected with WNV. The risk that WNV may pass to a fetus or an infant through breast milk is still being evaluated. Talk with your doctor if you have concerns.

How can West Nile Virus be prevented?

The best way to avoid WNV infection is to prevent mosquito bites:

  • Use insect repellent. The Centers for Disease Control and Prevention (CDC) recommends the use of insect repellents containing active ingredients registered with the U.S. Environmental Protection Agency (EPA). Always follow manufacturer's directions carefully.
  • Be careful using repellant on the hands of children because repellents may irritate the eyes and mouth.
  • Wear protective clothing such as long sleeved shirts and pants.
  • Limit outdoor activity from dusk to dawn when mosquitoes are most active.
  • Avoid areas where mosquitoes may be present (i.e. shaded and wooded areas).
  • Maintain window and door screens to keep mosquitoes out of buildings.
  • Get rid of mosquito breeding sites by emptying standing water that collects in birdbaths, boats, buckets, tires, unused pools, roof gutters and other containers.

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