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"Encephalitis" means "inflammation of the brain," but it usually refers to brain inflammation caused by a virus. This severe and potentially life-threatening disease is rare.

A severe inflammation of the brain, encephalitis is usually caused by a mosquito-borne or, in some areas, a tickborne 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. Eastern equine encephalitis may produce permanent neurologic damage and is often fatal.

In encephalitis, intense lymphocytic infiltration of brain tissues and the leptomeninges causes cerebral edema, degeneration of the brain's ganglion cells, and diffuse nerve cell destruction.


Encephalitis generally results from infection with arboviruses specific to rural areas. In urban areas, it's most frequently caused by enteroviruses (coxsackievirus, poliovirus, and echovirus).

Other causes include herpes virus, mumps virus, human immunodeficiency virus, adenoviruses, and demyelinating diseases after measles, varicella, rubella, or vaccination.

Between World War I and the Depression, a type of encephalitis known as lethargic encephalitis, von Economo's disease, or sleeping sickness occurred with some regularity. The causative virus was never clearly identified, and the disease is rare today. Even so, the term sleeping sickness persists and is often mistakenly used to describe other types of encephalitis as well.

Signs and symptoms

All viral forms of encephalitis have similar clinical features, although certain differences do occur.

Usually, the acute illness begins with sudden onset off ever, headache, and vomiting and progresses to include signs and symptoms of meningeal irritation (stiff neck and back) and neuronal damage (drowsiness, coma, paralysis, seizures, ataxia, and organic psychoses). After the acute phase of the illness, coma may persist for days or weeks.

The severity of arbovirus encephalitis may range from sub clinical to rapidly fatal necrotizing disease. Herpes encephalitis also produces signs and symptoms that vary from subclinical to acute and often fatal fulminating disease. Associated effects include disturbances of taste or smell.


Doctors use several tests to diagnose encephalitis, including:

  • imaging tests , such as computed tomography (CT) scans or magnetic resonance imaging (MRI), to check the brain for swelling, bleeding, or other abnormalities
  • electroencephalogram (EEG), which records the electrical signals in the brain, to check for abnormal brain waves
  • 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
  • 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


The antiviral agent acyclovir is effective only against herpes encephalitis. Treatment of all other forms of encephalitis is entirely supportive.

Drug therapy includes phenytoin or another anticonvulsant, usually given l.V.; glucocorticoids to reduce cerebral inflammation and edema; furosemide or mannitol to reduce cerebral swelling; sedatives for restlessness; and aspirin or acetaminophen to relieve headache IInd reduce fever.

Other supportive measures include adequate fluid and electrolyte intake to prevent dehydration and antibiotics for an associated infection such as pneumonia. Isolation is unnecessary.

In areas where arboviral encephalitis is prevalent, insecticide spraying may be used to control outbreaks. Wearing insect repellent and avoiding outdoor activities when mosquitoes are active may also be helpful.

A vaccine for Japanese encephalitis is available in the United States. People traveling to areas of the world where this disease is prevalent should be vaccinated. A vaccine for tick-borne encephalitis is available in Europe.

Administering antiviral medication (e.g., acyclovir) as soon as possible when encephalitis caused by herpes virus is suspected may prevent serious neurological complications.

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