La Crosse: Symptoms, Diagnosis, and Treatment

Key points

  • La Crosse virus infection can result in febrile illness or neurologic disease, including meningitis or encephalitis.
  • If you think you or a family member might have La Crosse, talk with your healthcare provider.
  • There is no specific treatment for La Crosse.
  • Rest, fluids, and pain medications may relieve symptoms.
Parent checking child's tempature with a thermometer


Most people infected with La Crosse virus do not have symptoms. For people with symptoms, the time from infected mosquito bite to feeling sick (incubation period) ranges from 5 to 15 days.

  • Initial symptoms can include fever (usually lasting 2-3 days), headache, nausea, vomiting, fatigue (tiredness), and lethargy (reduced activity or alertness).
  • La Crosse virus can cause severe disease, such as inflammation of the brain (encephalitis).
    • Symptoms of severe disease include high fever, headache, neck stiffness, stupor, disorientation, coma, seizures, muscle weakness, vision loss, numbness, and paralysis.
    • Severe disease occurs most frequently in children under the age of 16 years.
    • Recovery time from severe illness varies and some effects can persist over time. These can include recurrent seizures and thinking or behavioral problems.
    • Most patients recover though death does occur rarely (<1%).

Take actions to prevent La Crosse in you and your family.‎

There are things that you and your family can do to lower your risk of La Crosse. Listen to the effect that La Crosse had one family's life and ways to protect yourself.


If you think you or a family member might have La Crosse, talk with your healthcare provider.

  • Healthcare providers diagnose La Crosse based on:
    • Signs and symptoms
    • History of living in or traveling to an area where La Crosse virus is known to circulate
    • History of possible exposure to the mosquitoes that can carry La Crosse virus
    • Laboratory testing of blood or spinal fluid
  • Your healthcare provider can order tests to look for La Crosse virus infection or other infections that cause similar symptoms.

To learn more about testing, visit our Healthcare Providers page.


  • There are no vaccines to prevent or medicines to treat La Crosse. Antibiotics do not treat viruses.
  • Rest, fluids, and over-the-counter pain medications may relieve some symptoms.
  • Patients with severe disease often need to be hospitalized to receive support for breathing, staying hydrated, or reducing swelling in the brain.

To learn more about treatment, visit our Healthcare Providers page.