West Nile virus is present in Michigan every summer, with dozens of human cases and multiple deaths reported statewide in recent years. Reducing mosquito exposure through professional yard treatment is the most effective prevention available to homeowners.
West Nile Virus in Michigan: The Facts
West Nile virus (WNV) has been endemic in Michigan since it was first detected in the state in 2001. The virus is maintained in a cycle between mosquitoes and birds, with humans and horses as incidental hosts. Culex species mosquitoes — particularly Culex pipiens, the common house mosquito — are the primary vectors transmitting WNV to humans in Michigan.
Michigan consistently ranks among the top states for West Nile virus activity. The Michigan Department of Health and Human Services tracks WNV cases annually, and the numbers are concerning:
In recent years, Michigan has reported between 30 and 200+ human WNV cases annually, with multiple fatalities each year. Washtenaw County is included in the surveillance area with positive mosquito pools detected regularly during summer months. The actual number of infections is estimated to be significantly higher than reported cases, since roughly 80% of people infected with West Nile virus show no symptoms at all.
Symptoms and Health Risks
West Nile virus affects people differently depending on age and immune status:
No Symptoms (80% of infections): Most people infected with WNV never know they had it. They develop immunity without experiencing illness. However, even asymptomatic infections mean the virus was circulating in the body, which underscores how common transmission actually is.
West Nile Fever (roughly 20% of infections): Symptoms include fever, headache, body aches, fatigue, nausea, and sometimes a skin rash or swollen lymph nodes. Symptoms typically appear 2–14 days after a mosquito bite and resolve within days to weeks. Some patients report prolonged fatigue lasting months.
Severe Neuroinvasive Disease (less than 1% of infections): In rare cases, WNV crosses into the central nervous system causing meningitis (inflammation of the membranes surrounding the brain), encephalitis (inflammation of the brain), or acute flaccid paralysis. Neuroinvasive WNV has a fatality rate of approximately 10%, and many survivors experience permanent neurological effects. This severe form disproportionately affects adults over 60 and people with compromised immune systems.
Who Is Most at Risk?
While anyone can contract West Nile virus from a mosquito bite, certain groups face elevated risk of severe outcomes:
Adults over 60: The risk of neuroinvasive disease increases significantly with age. People over 70 are at the highest risk of serious complications and death from WNV.
Immunocompromised individuals: People undergoing chemotherapy, organ transplant recipients on immunosuppressive drugs, and those with conditions affecting immune function are more vulnerable to severe WNV infection.
Outdoor workers: People who spend extended hours outdoors during peak mosquito activity (dawn and dusk) have greater cumulative exposure to potentially infected mosquitoes.
Children and healthy adults are less likely to develop severe disease but are not immune to infection. With no vaccine and no specific treatment available for West Nile virus, prevention through mosquito bite avoidance is the only protection strategy.
When Is Risk Highest in Ann Arbor?
West Nile virus transmission in the Ann Arbor area follows a predictable seasonal pattern. Risk begins building in June as Culex mosquito populations grow, peaks in August and September when infected mosquito populations are at their highest, and declines after the first frost.
August and September are consistently the months with the most reported human WNV cases in Michigan. This late-season peak occurs because the virus needs time to amplify in the bird-mosquito cycle — by late summer, a higher percentage of the mosquito population carries the virus.
Prevention: What Actually Works
Since there is no vaccine for West Nile virus, prevention comes down to reducing mosquito bites. Here are the most effective strategies, ranked by impact:
1. Professional Mosquito Treatment: A seasonal barrier spray program reduces mosquito populations on your property by 85–90%. This is the single most effective step a homeowner can take to reduce WNV exposure for everyone who uses the yard — family members, children, guests, and pets. Regular treatment from April through October covers the entire transmission season.
2. Eliminate Breeding Sites: Dump any standing water on your property weekly. Culex mosquitoes prefer stagnant water in man-made containers — clogged gutters, old tires, flowerpot saucers, and pet water dishes are prime breeding sites. Eliminating these sources reduces the local mosquito population.
3. Personal Protection: When spending time outdoors during dawn and dusk, use EPA-registered insect repellents containing DEET (20–30%), picaridin, or oil of lemon eucalyptus. Wear long sleeves and pants during peak mosquito hours. These measures provide personal protection but do not reduce the overall mosquito population.
4. Home Barriers: Ensure window and door screens are intact and free of holes. Culex mosquitoes are particularly active at night, and they readily enter homes through damaged screens. Running air conditioning with windows closed during peak mosquito hours reduces indoor bite risk.
Why Mosquito Control Matters Beyond Comfort
Many people think of mosquito control as a comfort service — who wants to get bitten? But West Nile virus adds a genuine public health dimension. Every mosquito bite in Michigan carries some level of WNV risk during transmission season. Reducing the number of bites your family receives over the course of a summer directly reduces the cumulative probability of infection.
For families with elderly members, young children playing in the yard, or anyone who enjoys spending summer evenings outdoors, professional mosquito control is an investment in health protection, not just comfort. The eco-friendly treatment options available today mean you can reduce mosquito populations without compromising on environmental values.
Protect Your Family This Season
Do not wait for the health department advisory. Request a free quote from Mosquito Time or call (734) 985-2899 to set up seasonal protection before mosquito season begins. Professional treatment is the most effective way to reduce West Nile virus risk on your property.