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West Nile virus (WNV)
- West Nile virus (WNV) is carried by certain types of mosquitoes in Michigan
- It is a potentially serious disease that can affect anyone, but people over age 60 are more likely to get the severe form of WNV illness.
- The risk of bites from infected mosquitoes is highest for people who work or play outdoors
- Wearing insect repellent when outdoors (especially at dawn and dusk) is important to prevent WNV.
Sick acting or dead birds, especially crows and blue jays may be an indication of WNV in a community.
Current WNV Outbreak Status
Who is at risk?
- Anyone living in an area where West Nile virus is present in mosquitoes can get infected.
- In Michigan, outbreaks of WNV have been occurring every summer since 2002.
- Urban areas in Southeastern Lower Michigan (Macomb, Oakland, and Wayne counties) and Western Lower Michigan (Kent county) have historically seen the most West Nile virus activity.
- The risk of infection is highest for people who work outside or participate in outdoor activities because of greater exposure to mosquitoes.
- Serious illness can occur in people of any age.
- However, people over 60 years of age are at the greatest risk for severe disease.
- People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk for serious illness.
Signs and Symptoms
What are the symptoms of West Nile virus infection?
No symptoms in most people. Most people (8 out of 10) who become infected with West Nile virus do not develop any symptoms.
Febrile illness in some people. About 1 in 5 people who are infected will develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with this type of West Nile virus disease recover completely, but fatigue and weakness can last for weeks or months.
Severe symptoms in a few people. About 1 out of 150 people who are infected will develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues).
- The symptoms of neurologic illness can include headache, high fever, neck stiffness, disorientation, coma, tremors, seizures, or paralysis.
- Serious illness can occur in people of any age. However, people over 60 years of age are at the greatest risk for severe disease. People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk for serious illness.
- Recovery from severe disease may take several weeks or months. Some of the neurologic effects may be permanent.
- About 1 out of 10 people who develop severe illness affecting the central nervous system will die.
Diagnosis and Testing
What should I do if I think a family member might have West Nile virus disease?
- Consult a healthcare provider for evaluation and diagnosis.
How is West Nile virus disease diagnosed?
- Diagnosis is based on a combination of clinical signs and symptoms and specialized laboratory tests of blood or spinal fluid.
- These tests typically detect antibodies that the immune system makes against the viral infection.
I know that birds sometimes get sick and die of West Nile. What should I do if I want to report sick or dead wildlife around my home or community?
- You can report sick or dead wildlife to the Michigan Department of Natural Resources.
What is the treatment for West Nile virus disease?
- There are no medications to treat or vaccines to prevent West Nile virus infection.
- Over-the-counter pain relievers can be used to reduce fever and relieve some symptoms.
- People with milder symptoms typically recover on their own, although some symptoms may last for several weeks.
- In more severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.
How can I prevent West Nile virus?
The most effective way to avoid West Nile virus disease is to prevent mosquito bites:
- Use insect repellents when you go outdoors. Repellents containing DEET, picaridin, IR3535, and some oil of lemon eucalyptus and para-menthane-diol products provide longer-lasting protection.
- Wear long sleeves and pants from dusk through dawn when many mosquitoes are most active.
- Install or repair screens on windows and doors. If you have it, use your air conditioning.
- Help reduce the number of mosquitoes around your home. Empty standing water from containers such as flowerpots, gutters, buckets, pool covers, pet water dishes, discarded tires, and birdbaths.
- Fight the Bite -West Nile Virus Educational Pamphlet
- Control Mosquitoes Tip 'n Toss: Mosquito Control Advice
- Public Health Confronts the Mosquito: Developing Sustainable Mosquito Control Programs
- Guidelines for the Emergency Management of Mosquito-Borne Disease
- Communicating About Effective Mosquito Control: Toolkit for Communities
- Communicable Disease Division Publication Order Form Order "West Nile Virus Fight the Bite" pamphlet free of charge for Michigan local health departments, healthcare providers, social services agencies, and others.
Data, Statistics, and Maps
Michigan WNV Maps & Tables
- Map: Human Cases by County, Current
- Map: Mosquitos Testing Positive for West Nile by County, Current
- Map: Sick/Dead Birds, Reported by County, Current
- Map: Birds Testing Positive for West Nile by County, Current
- Map: Horse Cases, Current
National WNV Maps & Statistics