California Encephalitis Clinical Presentation

Updated: May 14, 2021
  • Author: Folusakin O Ayoade, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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History and Physical Examination

The incubation period of California encephalitis is usually 3-7 days. A prodromal phase of 1-4 days commonly precedes the onset of encephalitis. This phase manifests as any or all of the following:

  • Fever

  • Chills

  • Nausea

  • Vomiting

  • Headache

  • Abdominal pain

The encephalitis is characterized by fever and somnolence, which may progress to obtundation. Although most patients make uneventful recoveries, electroencephalographic findings are abnormal 1-5 years later in 75% of cases, emotional lability is persistent in 10%, and epilepsy is a chronic problem in 6%-10% of all diagnosed cases. Although uncommon, frank neurologic deficit can also occur. [3] Twenty percent of children develop focal neurologic signs (eg, asymmetrical reflexes, Babinski signs), and 10% of patients develop coma. Periodic lateralizing epileptiform discharges (PLEDS) can be seen in the temporal lobe. The total duration of illness rarely exceeds 10-14 days.

Two reports in the literature have described LaCrosse encephalitis manifesting as signs and symptoms of herpes simplex encephalitis. [4, 5]

In adults, infection is asymptomatic or causes a benign febrile illness or aseptic meningitis.

Physical findings may include the following:

  • Fever

  • Lethargy

  • Focal neurologic findings (eg, aphasia)

  • Incoordination

  • Focal motor abnormalities

  • Paralysis



Complications may be associated with more severe disease. These include the following:

  • Epilepsy (commonest and most serious)
  • Cognitive and memory deficits
  • Lethargy
  • Aphasia
  • Incoordination
  • Focal motor abnormalities
  • Paralysis