In this disorder, a person develops severe inflammation and swelling of the brain. This disorder may produce only mild effects, or it may be severe, causing permanent neurologic damage and even death.

What causes it?

In rural areas, encephalitis is usually caused by a virus carried by a mosquito or a tick. However, the disorder may be transmitted by other means. For example, a person may get the disorder by accidentally inhaling or ingesting the virus - perhaps by drinking infected goat's milk.

In urban areas, encephalitis is most frequently caused by a group of viruses called enteroviruses, which infect the gastrointestinal tract and are discharged in feces. Encephalitis also may be caused by other types of viruses (herpesvirus, mumps virus, HIV, and adenoviruses). It may also result from diseases that destroy the protective sheath surrounding the nerves or spinal cord. Such diseases may occur following measles, chickenpox, rubella, or vaccination.

What are its symptoms?

All forms of encephalitis caused by viruses produce similar signs and symptoms, although certain differences do occur. Usually, the acute illness begins with sudden onset of fever, headache, and vomiting. Later, the person may experience neck and back stiffness. Many symptoms may result from physiologic changes to the brain and nervous system: drowsiness, coma, paralysis, seizures, inability to coordinate voluntary muscular movements and, possibly, psychotic behavior. After the acute phase of illness, coma may persist for days or weeks.

The severity of encephalitis symptoms varies greatly. Encephalitis caused by mosquito- or tick-borne virus may be so mild that it goes unnoticed, or it may be rapidly fatal. Encephalitis caused by herpesvirus also produces effects that range from mild illness to acute and potentially fatal disease. Severe disease may occur suddenly and with great intensity.

How is it treated?

The antiviral drug Avirax is effective in treating encephalitis caused by herpesvirus, but it does not work against encephalitis caused by other viruses. Treatment of all other forms of encephalitis addresses the effects of illness, but does not eliminate the causal viruses. Drug therapy includes antiseizure drugs such as Dilantin, usually administered intravenously; glucocorticoids to reduce cerebral inflammation and swelling; Lasix or Osmitrol to reduce cerebral swelling; sedatives for restlessness; and aspirin or Tylenol (or another drug with acetaminophen) to reduce fever.

Other treatment measures include making sure the person gets enough fluids and electrolytes to prevent dehydration and providing antibiotics to treat any associated infection, such as pneumonia.