Mosquito-Borne Diseases
Mosquito Bites Can Make You Sick
Almost everyone in the world has been bitten by a mosquito. Although most types of mosquitoes are just nuisance mosquitoes, some types of mosquitoes spread germs (viruses and parasites) that can cause disease. For most of these germs, no vaccines or specific medicines are available.
Mosquitoes bite during the day and night, live indoors and outdoors, and search for warm places as temperatures begin to drop. Some mosquitoes hibernate in enclosed spaces, like garages, sheds, and under (or inside) homes, to survive cold temperatures. Typically, mosquito season starts in the summer and continues into fall.
Disease epidemics from viruses spread by mosquitoes are happening more often. West Nile virus is the most common virus spread by mosquitoes in the continental United States. However, people in the United States can also get sick from less common viruses spread by mosquitoes, like eastern equine encephalitis (EEE) or St. Louis encephalitis. These viruses have hospitalized over one hundred people in Michigan, and caused several deaths. Some of these viruses have also caused equine illness with over 200 horse deaths confirmed in Michigan.
Prevent Mosquito Bites
The best way to prevent illnesses from mosquito bites is to protect yourself and your family from bites.
Use insect repellent
Environmental Protection Agency (EPA)-registered insect repellents are proven safe and effective, even for those who are pregnant and breastfeeding.
Look for these ingredients on product labels: DEET, picaridin, oil of lemon eucalyptus, and permethrin.
Always follow repellent label instructions.
Cover up
Wear loose-fitting, long-sleeved shirts and long pants when outside.
Mosquitoes may bite through thin clothing, so spraying clothes with a repellent can provide extra protection.
Keep mosquitoes outside
Use air conditioning or window and door screens.
If you are not able to protect yourself from mosquitoes inside your home or hotel, sleep under a mosquito net.
Clean mosquito breeding sites
Drain standing water from items in your yard. A small amount of standing water can be enough for mosquitoes to lay eggs. Be sure to empty water from buckets, cans, pool covers, flowerpots, and other items.
Clean up potential mosquito breeding places around your yard. Throw away or cover up stored tires or items that aren’t being used. Clean pet bowls weekly. Check if rain gutters are clogged.
Plan ahead for travel
Learn about destination-specific health risks and recommendations by visiting the
CDC Travelers’ Health website.
Remember to pack insect repellent to prevent mosquito bites.
EPA-registered Insect Repellents
Environmental Protection Agency (EPA)-registered insect repellents are proven safe and effective, even for those who are pregnant and breastfeeding.
Mosquito-Borne Diseases
Below are a few mosquito-borne illnesses monitored in Michigan.
West Nile Virus
West Nile Virus Overview
West Nile virus (WNV) is the leading cause of mosquito-borne disease in the continental United States. It is most commonly spread to people by the bite of an infected mosquito. Cases of West Nile occur during mosquito season, which starts in the summer and continues through fall.
There are no vaccines to prevent or medicines to treat West Nile in people. Fortunately, most people infected with West Nile virus do not feel sick. About 1 in 5 people who are infected develop a fever and other symptoms. About 1 out of 150 infected people develop a serious, sometimes fatal, illness. Reduce your risk of West Nile by preventing mosquito bites.
How It Spreads
- West Nile virus circulates in the environment between mosquitoes (primarily Culex species) and birds.
- People become infected with the virus when mosquitoes feed on infected birds and then bite people.
- People are considered dead-end hosts because unlike birds, they do not develop high enough levels of virus in their bloodstream and cannot pass the virus on to other biting mosquitoes.
- The virus is rarely transmitted from person-to-person by blood transfusion, organ transplantation, and mother to baby, during pregnancy, delivery, or breastfeeding.
- Prevent getting sick with West Nile by preventing mosquito bites.
Prevention
- West Nile virus is spread to people through the bite of an infected mosquito. Mosquitoes bite during the day and night.
- There are no vaccines or medicines to prevent West Nile.
- The best way to prevent West Nile is to protect yourself from mosquito bites.
- Additional information about protecting yourself from mosquito bites is available on the CDC Mosquitoes website.
Eastern Equine Encephalitis
Eastern Equine Encephalitis Overview
Eastern equine encephalitis (EEE) virus is spread to people by the bite of an infected mosquito.
Only a few cases are reported in the United States each year. Most cases occur in eastern or Gulf Coast states.
Although rare, eastern equine encephalitis is very serious. Approximately 30% of people with eastern equine encephalitis die, and many survivors have ongoing neurologic problems. Symptoms of eastern equine encephalitis can include fever, headache, vomiting, diarrhea, seizures, behavioral changes, and drowsiness.
There are no vaccines to prevent or medicines to treat eastern equine encephalitis.
You can reduce your risk of infection with eastern equine encephalitis virus by preventing mosquito bites.
How It Spreads
- Eastern equine encephalitis virus circulates in the environment between mosquitoes and birds typically found in freshwater hardwood swamps.
- People and some other animals (e.g., horses and emus) become infected often by different mosquitoes (known as bridge vectors) that feed on both birds and animals.
- People and horses are considered “dead-end” hosts. This means they do not spread the virus, even though they get sick, to mosquitoes that bite them.
- Eastern equine encephalitis can also be transmitted through organ transplantation.
Prevention
- Eastern equine encephalitis virus is spread to people through the bite of an infected mosquito. Mosquitoes bite during the day and night. Anyone who spends time in a place where eastern equine encephalitis virus infection occurs is at risk.
- There are no human vaccines or medicines to prevent eastern equine encephalitis.
- The best way to prevent eastern equine encephalitis is to protect yourself from mosquito bites.
- Additional information about protecting yourself from mosquito bites is available on the CDC Mosquitoes website.
Jamestown Canyon Virus
Jamestown Canyon Virus Overview
Jamestown Canyon virus (JCV) is spread to people by infected mosquitoes. The virus is found throughout much of the United States, but most cases are reported from the upper Midwest. Cases occur from late spring through mid-fall.
Fever, headache, and fatigue are common symptoms with Jamestown Canyon. Jamestown Canyon can cause severe disease, including encephalitis (inflammation of the brain).
There are no vaccines to prevent or medicines to treat Jamestown Canyon. Reduce your risk of infection by preventing mosquito bites.
How It Spreads
- Jamestown Canyon virus circulates in the environment between mosquitoes and animals, typically deer.
- Infected mosquitoes can then spread the virus to people and other animals by biting them.
- People are considered “dead-end” hosts. This means they do not spread the virus, even when they are sick, to mosquitoes that bite them.
- Jamestown Canyon virus is not spread by coughing, sneezing, touching, or other contact with someone who is infected.
Prevention
- Jamestown Canyon virus is spread to people through the bite of an infected mosquito. Mosquitoes bite during the day and night.
- There are no vaccines or medicines to prevent Jamestown Canyon.
- The best way to prevent eastern equine encephalitis is to protect yourself from mosquito bites.
- Additional information about protecting yourself from mosquito bites is available on the CDC Mosquitoes website.
What is LCHD doing?
Case Follow-up
If someone becomes sick from a mosquito bite, the LCHD Personal and Preventive Health Services Division follows-up to ensure proper treatment. We also collect information to identify where the person was exposed to infected mosquitoes. This helps us understand which mosquito-borne diseases may exist in our community.
Health Education and Outreach
It only takes one bite from an infected mosquito to make you sick! The LCHD Health Promotion Team educates the community about the risks of mosquito-borne disease at community events and creates educational materials to reinforce the importance of preventing mosquito bites and cleaning up mosquito breeding areas around your home.
Mosquito Surveillance
This video shows mosquitoes collected through LCHD’s local surveillance program.
Last Modified April 24, 2026
