La Crosse encephalitis (LAC) is transmitted to humans by mosquito bites. The majority of those infected with the virus do not exhibit any symptoms. Some people may suffer severe illnesses like encephalitis (brain inflammation). Severe disease is more common in children under the age of 16. Most instances are found in the upper Midwest, mid-Atlantic, and southern states. By avoiding mosquito bites, you may reduce your risk of contracting the disease.


Most persons infected with this virus will either have no symptoms or a minor sickness similar to the flu. The quick onset of symptoms is typical and can occur anywhere from one to two weeks after being bitten by an infected insect. There is a risk of encephalitis for a specific subset of the population, particularly youngsters. 

There is a mortality rate of less than one percent in cases of encephalitis. Most patients fully recover, but some individuals are left with long-term difficulties with their neurological system, such as epileptic seizures or cognitive anomalies.

The majority of severe cases begin with the following:

  • fever
  • headache
  • nausea
  • weakness

The symptoms of the sickness might quickly escalate into:


Talk to your healthcare professional if you or a family member is experiencing symptoms of La Crosse encephalitis (LAC) virus illness.

Infection with the La Crosse encephalitis (LAC) virus is diagnosed by medical professionals based on the following:

  • history of living in or visiting a region where there is evidence that the LAC virus is circulating
  • history of probable exposure to mosquitoes that might have carried the LAC virus in their bites
  • examination in the laboratory of the patient’s blood or spinal fluid
  • signs and symptoms

Your healthcare practitioner can run tests to search for an infection caused by the LAC virus or other viruses that generate symptoms that are very similar to those symptoms.


La Crosse encephalitis (LAC) has no particular therapy; clinical care is supportive. Patients with severe meningeal symptoms frequently require pain relief for:

  • headaches
  • antiemetic medication
  • rehydration for nausea and vomiting

Patients suffering from encephalitis must be closely monitored for high intracranial pressure, convulsions, and an inability to protect their airways.

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