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What is Encephalitis ?

Encephalitis is a severe inflammation of the brain characterized by intense lymphocytic infiltration of brain tissues and the leptomeninges. This causes cerebral edema, degeneration of the brain's ganglion cells, and diffuse nerve cell destruction.

Encephalitis is usually caused by a mosquito-borne or, in some areas, a tick-borne virus. Transmission by means other than arthropod bites may occur through ingestion of infected goat's milk and accidental injection or inhalation of the virus.

Causes of Encephalitis

Encephalitis is caused by several types of viral infections. Herpesvirus is the most common cause and encephalitis can also result from infection following smallpox vaccination and reactivation of viral infection such as influenza, chickenpox, measles, mumps, and rabies (usually in undeveloped countries).

Arthropod-borne viruses, which are usually transmitted by mosquitoes, cause arboviral encephalitis. People who live in warm, moist climates are at higher risk for this type.

Signs & Symptoms of Encephalitis

Most people infected with viral encephalitis have only mild symptoms — headache, irritability or lethargy — or no symptoms, and the illness doesn't last long. Serious cases can cause:

  • Drowsiness
  • Confusion and disorientation
  • Sudden fever
  • Severe headache
  • Nausea and vomiting
  • Visual disturbances
  • Tremor or convulsions
  • Stiff neck
  • Seizures

Symptoms may progress rapidly, changing from mild to severe within several days or even several hours.

Diagnostic Tests

During an encephalitis epidemic, diagnosis is readily made from clinical findings and patient history. Sporadic cases are difficult to distinguish from other febrile illnesses, such as gastroenteritis or meningitis. The following tests help establish a diagnosis:

Blood tests to confirm the presence of bacteria or viruses in the blood, and whether a person is producing antibodies (specific proteins that fight infection) in response to a germ

Serologic studies in herpes encephalitis may show rising titers of complement-fixing antibodies. In some types of encephalitis, serologic tests of blood may be diagnostic.

Lumbar puncture, also known as a spinal tap, in which cerebrospinal fluid (the fluid that surrounds the brain and spinal cord) is checked for signs of infection

EEG reveals abnormalities such as generalized slowing of waveforms.

Computed tomography scanning may be ordered to check for temporal lobe lesions that indicate herpesvirus and to rule out cerebral hematoma.


The antiviral agent vidarabine is effective only against herpes encephalitis and only if it's administered before the onset of coma.

Treatment of all other forms of encephalitis is supportive. Drug therapy includes reduction of intracranial pressure (lCP) with I.V. mannitol and corticosteroids (to reduce cerebral inflammation and resulting edema); phenytoin or another anticonvulsant, usually given I.V.; sedatives for restlessness; and aspirin or acetaminophen to relieve headache and reduce fever.

Other supportive measures include adequate fluid and electrolyte intake to prevent dehydration and appropriate antibiotics for associated infections, such as pneumonia or sinusitis; maintenance of the patient's airway; administration of oxygen to maintain arterial blood gas levels; and maintenance of nutrition, especially during periods of coma. Isolation is unnecessary.
Prevention Tips

Controlling mosquitoes (a mosquito bite can transmit some viruses) may reduce the chance of some infections that can lead to encephalitis.

Animal vaccination is important to prevent encephalitis caused by rabies virus. Vaccination is available to prevent a form of viral encephalitis that often affects people living in dorms or in the military.

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