Symptoms of La Crosse

For Everyone

Key points

  • La Crosse virus infection can result in mild febrile illness or severe neurologic disease, including meningitis or encephalitis.
  • If you think you or a family member might have La Crosse, talk to your healthcare provider.
A parent places a hand on a child's forehead while examining a thermometer.

Symptoms

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

Initial symptoms can include:

  • Fever (usually lasting 2-3 days)
  • Headache
  • Nausea
  • Vomiting
  • Fatigue (tiredness)
  • Lethargy (reduced activity or alertness)

Severe illness

La Crosse virus can cause severe illness, such as inflammation of the brain (encephalitis).

Symptoms of severe illness include:

  • High fever
  • Headache
  • Neck stiffness
  • Stupor
  • Disorientation
  • Coma
  • Seizures
  • Muscle weakness
  • Vision loss
  • Numbness
  • Paralysis

Treatment

No medicines are available to treat La Crosse. Rest, fluids, and over-the-counter pain medications may relieve some symptoms.

Outcome and complications

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%).

For Health Care Providers Clinical Signs and Symptoms of La Crosse Virus Disease

Risk factors

Severe illness occurs most frequently in children under 16 years old.

Testing and diagnosis

If you think you or a family member might have La Crosse, talk to 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 spread La Crosse virus
  • Laboratory testing

Your healthcare provider can order tests to look for La Crosse virus or other infections that cause similar symptoms.

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Content Source:
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)