Jamestown Canyon Virus (JCV) is a mosquito-borne virus found throughout most of the United States. It was first identified in 1961 in mosquitoes from Jamestown Canyon, Colorado. Although the number of cases reported each year is typically low, it is increasingly being recognized as a public health concern.

Which Mosquito Is the Primary Vector?

Several species of mosquitoes that commonly bite people are able to spread JCV. The Aedes, Culiseta, and Anopheles species are the primary vectors. These mosquitoes emerge in the spring and are often found in wooded areas.

Where is JCV Found

The number of reported human cases of the illness it causes (Jamestown Virus infection) has risen sharply in the northeastern and midwestern U.S. during the past decade. Wisconsin and Minnesota have the highest number of reported cases of the more serious form of the disease that attacks the nervous system.

Jamestown Canyon virus neuroinvasive disease cases reported to CDC by year, 2018–2022

Jamestown Canyon Virus cases
Source: Centers for Disease Control and Prevention,
National Notifiable Diseases Surveillance System


The time from mosquito bite to feeling ill ranges from a few days to two weeks. Symptoms can range from mild to severe. Most infections occur in adults, during the summer, and are asymptomatic. More serious symptoms can include fever and acute meningoencephalitis (inflammation of the brain and surrounding tissues).

Mild Symptoms May Include

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

Severe Symptoms May Include

  • Stiff neck
  • Confusion
  • Loss of coordination
  • Difficulty speaking
  • Seizures

Who Is Most at Risk?

Anyone can get Jamestown Canyon, but individuals who spend more time outdoors are at a higher risk of being bitten by an infected mosquito. Illness can occur in any age group. The median age of those who have contracted Jamestown Canyon virus is 48 years. Men are at slightly higher risk.


No vaccine or specific medications are available for preventing or treating Jamestown Canyon virus infection. About half of the patients reported to have become infected with Jamestown Canyon virus have been hospitalized for supportive treatment. Death from Jamestown Canyon infection is rare, but has been documented.


Mosquitoes capable of infecting humans with JCV are active during the day and night. To help prevent bites, when going outside use repellents containing DEET (or other EPA-registered active ingredients) according to label directions. The American Academy of Pediatrics and the Centers for Disease Control and Prevention note that products containing up to 30% DEET are appropriate for children over two months of age. For more information, please visit our prevention page.