Symptoms:

Some patients may have symptoms of a cold or stomach infection before encephalitis symptoms begin.

When a case of encephalitis is not very severe, the symptoms may be similar to those of other illnesses, including:

• Fever that is not very high
• Mild headache
• Low energy and a poor appetite

Other symptoms include:

• Clumsiness, unsteady gait
• Confusion, disorientation
• Drowsiness
• Irritability or poor temper control
• Light sensitivity
• Stiff neck and back (occasionally)
• Vomiting

Symptoms in newborns and younger infants may not be as easy to recognize:

• Body stiffness
• Irritability and crying more often (these symptoms may get worse when the baby is picked up)
• Poor feeding
• Soft spot on the top of the head may bulge out more
• Vomiting

Emergency symptoms:

• Loss of consciousness, poor responsiveness, stupor, coma
• Muscle weakness or paralysis
• Seizures
• Severe headache
• Sudden change in mental functions:
  • "Flat" mood, lack of mood, or mood that is inappropriate for the situation
  • Impaired judgment
  • Inflexibility, extreme self-centeredness, inability to make a decision, or withdrawal from social interaction
  • Less interest in daily activities
  • Memory loss (amnesia), impaired short-term or long-term memory

Signs and tests:

An examination may show:

• Abnormal reflexes
• Increased intracranial pressure
• Mental confusion
• Mouth ulcers
• Muscle weakness
• Neck stiffness
• Signs in other organs, such as the liver and lungs
• Skin rash
• Speech problems

Tests may include:

• Brain MRI
• CT scan of the head
• Culture of cerebrospinal fluid (CSF), blood, or urine (however, this test is rarely useful)
• Electroencephalogram (EEG)
• Lumbar puncture and CSF examination
• Tests that detect antibodies to a virus (serology tests)
• Test that detects tiny amounts of virus DNA (polymerase chain reaction -- PCR)