Jamestown Canyon Virus: About

Jamestown Canyon is an illness spread to humans by the bite of an infected mosquito. It is currently unknown which types of mosquitoes spread Jamestown Canyon virus in Wisconsin.

Jamestown Canyon virus is closely related to La Crosse encephalitis virus. Jamestown Canyon virus is most common in Wisconsin and Minnesota. The virus is relatively rare in Wisconsin, but recently there has been a large increase in cases.

Anyone can get Jamestown Canyon, but people who spend more time outdoors are at a higher risk of being bitten by an infected mosquito. Mosquitoes are usually most active in Wisconsin from May to September.

Mosquitoes can be found in areas with standing water, which they need to breed. It is important to remove standing water sources, such as containers, leaves, and yard debris, to reduce breeding habitats in your yard. For more tips, please visit our Mosquito Bite Prevention page.

Map of Jamestown Canyon Virus Cases in Wisconsin

 How is Jamestown Canyon virus spread to humans?

Jamestown Canyon virus is spread to humans through the bite of an infected mosquito.
  • Mosquitoes become infected with Jamestown Canyon virus by feeding on infected mammals, mostly white-tailed deer. Image of a deer's shadow
    • After feeding on an animal that has Jamestown Canyon, the virus may end up inside of the mosquito.
    • Once it has the virus, a mosquito can spread the virus to other mammals, including humans, when they take another blood meal.
  • Mosquitoes are usually most active in Wisconsin during the summer months, into the fall.
  • Few mosquitoes actually carry the virus, but it is important to take prevention measures when spending time outside.

Jamestown Canyon is preventable. Visit our Mosquito Bite Prevention page to learn how to prevent mosquito bites.

 What are the signs and symptoms of Jamestown Canyon?

Symptoms can show up two to 14 days after being bitten by an infected mosquito.

Most people who are infected with Jamestown Canyon virus never develop obvious signs of infection. Others may develop mild symptoms like fever, fatigue, and headache. Infection with the virus can lead to severe illness, including neurological symptoms, but this is rare. Severe illness is more likely to develop in the elderly or in people with compromised immune systems. Death from an infection with Jamestown Canyon is rare, but has been documented. If you have had Jamestown Canyon, you cannot get it again.

Mild signs and symptoms:

  • Fever
  • Headache
  • Fatigue
  • Chills
  • Muscle aches
  • Nausea and/or vomiting
  • Joint pain

Severe signs and symptoms:

  • Meningoencephalitis (inflammation of the brain and surrounding tissues)
    • Increasing lethargy
    • Altered mental status
  • Meningitis (inflammation of the membranes around the brain and spinal cord)
    • Severe headache
    • Neck stiffness

 How is Jamestown Canyon virus treated?

There is currently no treatment or vaccine for Jamestown Canyon. Over-the-counter pain relievers may be given to relieve symptoms. In severe cases, patients may need to be hospitalized to receive supportive treatment. If you believe you or a family member may have Jamestown Canyon, contact your doctor immediately.


DHS Resources
Centers for Disease Control and Prevention (CDC) Resources

Mosquito Bites Are Bad: An educational activity book for kids about preventing illnesses spread by mosquitoes.

    Partner Resources
    Jamestown Canyon is preventable. Visit our Mosquito Bite Prevention page to learn how to protect yourself from Jamestown Canyon and other illnesses spread by mosquitoes.

    Questions about illnesses spread by mosquitoes? Contact us!
    Phone: 608-267-9003 | Fax: 608-261-4976

    Last Revised: June 29, 2020