health

1. Definition .
   
2. Description .
   
3. Demographics .
   
4. Causes and Symptoms .
   
5. Diagnosis .
   
6. Treatment .
   
7. Prognosis .
8. Prevention .
   
9. The Future .

Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis EncephalitisEncephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis Encephalitis

Encephalitis is a severe infection or inflammation of the brain itself. It
should be distinguished from meningitis, which is an inflammation of
the protective membranes that cover the brain and line the spinal cord.
However, the two conditions can exist together. Encephalitis is usually
caused by viruses, but can also result from infections caused by bacteria,
fungi, or parasites.

Encephalitis is an illness that can range from mild cases with flu-like
symptoms to life-threatening, severe cases that can kill patients or leave
them with permanent problems. The severity of the illness varies
according to the patient’s age, the organism that is causing the encephalitis,
and the condition of the person’s immune system. Mild viral encephalitis
may have no symptoms at all, or a brief period of headaches,
tiredness, and irritability.
Severe encephalitis often begins with a prodrome, or a period of
warning symptoms. After the prodrome, victims of the disease may become
feverish, vomit, become drowsy, find that their eyes are sensitive to light,
complain of a stiff neck, or feel unsteady on their feet when they try to
walk. They should see their doctor at once. If they lose their memory, have
speech problems, are paralyzed, or go into a coma, they need emergency
medical treatment and should be taken to the hospital as soon as possible.

The exact number of cases of encephalitis in the United States in an
average year is difficult to estimate because mild cases may not be diagnosed,
and the reporting of severe cases is not standardized. Between
1,500 and 3,000 cases of viral encephalitis are reported to the Centers for
Disease Control and Prevention (CDC) each year, but most doctors
think that the actual number of cases is higher. According to the CDC,
it costs about $150 million each year to control the mosquitoes that
spread some types of viral encephalitis.

Some statistics for specific types of viral encephalitis are as follows:

• Japanese encephalitis: 30,000–50,000 cases each year in Asia;
  about one case per year in Americans traveling in Asia.
  
• Eastern equine encephalitis, found in the eastern United States:
  five cases per year on average.
  
• La Crosse encephalitis, found in California and the Great Lakes region:
  seventy cases per year on average.
• West Nile virus: about 1,200 cases per year in the United States.
• Herpes simplex encephalitis, caused by the virus that causes cold sores:
  about one person in every 250,000 per year in the United States.
• Encephalitis following measles: about one case per 1,000 infected persons.
• Encephalitis following chickenpox: one case in every 2,000 infected persons.
• Encephalitis following rabies: one tothree cases in the United States each year
  
  

Most cases of encephalitis in the United States are caused by viruses:

• Herpes simplex virus (HSV) 1 and 2. This is the virus responsible
  for cold sores and genital herpes.
  
• Poliovirus.
  
• Arboviruses. The arboviruses are a family of viruses transmitted to
  humans by infected mosquitoes, ticks, or other blood-sucking
  insects. These types of encephalitis include West Nile virus,
  Japanese encephalitis, equine encephalitis, La Crosse encephalitis,
  and St. Louis encephalitis.
  
• The rabies virus.

Toxoplasmosis, a disease caused by a parasite, and Lyme disease, a
bacterial infection, can cause encephalitis.

Symptoms of encephalitis in infants may include:

• Vomiting
  
• Body stiffness
  
• Crying that increases when the baby is picked up or held
  
• A fullness or bulge in the soft spot at the top of the baby’s head

In addition to the symptoms of encephalitis in adults discussed earlier,
people with severe infections may also have:

• Visual hallucinations
  
• Seeing double
  
• Personality changes
  
• Loss of sensation in some parts of the body
  
• Impaired judgment
  
• Muscle weakness
  

The patient’s history of recent travels, exposure
to animals or infected persons, or exposure to
the herpes simplex virus or arboviruses are important clues in diagnosis.
If the patient is unconscious or cannot speak, family members may be
asked for information about his or her recent activities.

The specific diagnostic tests that may be done depend partly on the
type of disease organism that the doctor suspects is causing the encephalitis.
Some common diagnostic tests include:

• Blood tests. Blood tests can be used to diagnose West Nile virus
  
• A neurological examination. This examination allows the doctor to
  evaluate the patient’s memory and other mental functions, sight
  and hearing, reflexes, gait and movement, mood, level of consciousness,
  and other functions of the nervous system that may
  be affected by encephalitis.
• Spinal tap. In a spinal tap, a small sample of spinal fluid is withdrawn
  through a needle inserted into the lower back. It can be
  tested for evidence of a bacterial or fungal infection. In some cases,
  a spinal tap can also be used to diagnose HSV encephalitis.
• Electroencephalogram (EEG). An EEG is a test that measures patterns
  of electrical activity in the brain. HSV encephalitis produces
  a telltale abnormal EEG pattern.
  
• Imaging studies of the brain. Computed tomography (CT) scans
  and magnetic resonance imaging (MRI) are the types of imaging
  studies most frequently used to diagnose encephalitis.
  
• Brain biopsy. In a brain biopsy, a surgeon removes a small sample
  of brain tissue to analyze it for the presence of HSV. This test is
  rarely done except when brain imaging or other tests for HSV do
  not provide definite results.
  

Treatment of mild encephalitis usually includes bed rest at home, drinking
lots of fluids, and taking over-the-counter pain relievers to bring down
fever and treat headaches. If the patient gets worse suddenly, or if the infection
is severe from the start, emergency treatment in a hospital is necessary.

Specific forms of treatment for encephalitis in the hospital may
include:

• Acyclovir for HSV encephalitis. Acyclovir is an antiviral drug that
  is given intravenously when the doctor suspects HSV encephalitis.
  It is given for a period of two to three weeks.
  
• If the encephalitis is caused by a bacterium, the doctor may prescribe
  antibiotics. Antibiotics cannot be used to treat encephalitis
  caused by viruses, however.
  
• Patients are monitored for signs of swelling of the brain, and they
  are given intravenous fluids to prevent dehydration.
  
• Patients who are having seizures are given anticonvulsants (antiseizure
  drugs).
  
• Sedatives may be given to patients who are restless or having
  trouble sleeping.
  
• Patients who are partially paralyzed or having trouble breathing are
  put on a respirator.

Patients who have had severe encephalitis may suffer permanent
damage if they survive. They may need physical therapy, speech therapy,
or psychological counseling after the acute illness has passed.

The prognosis for recovery from encephalitis depends on the virus or
other disease agent that is causing the infection, the patient’s age, and his
or her general state of health. In general, infants and the elderly are at the
greatest risk of death from encephalitis.
People with mild cases of encephalitis usually recover without longterm
complications.

The prognoses for specific types of encephalitis are as follows:

• Rabies encephalitis: 100 percent mortality.
  
• Japanese encephalitis: 60 percent mortality, usually within the first
  week of illness.
  
• Untreated HSV encephalitis: 50–75 percent of patients die within
  eighteen months. The fatality rate drops to 20 percent in patients
  treated with acyclovir. Forty percent of survivors have long-range
  learning disabilities, epilepsy, movement disorders, memory loss,
  and psychiatric problems.
  
• St. Louis encephalitis: 30 percent mortality.
  
• West Nile virus: 10 percent mortality.
  

Japanese encephalitis is the only encephalitis for which there is an effective
vaccine for humans. People planning a trip to Japan or eastern Asia
may want to consider being vaccinated before departure. There was a
vaccine for horses against West Nile virus but not one for humans as
of late 2008.

Other preventive measures to lower one’s risk of encephalitis
include:

• Draining water from bird baths, wading pools, and other outdoor
  water containers when not in use.
  
• Using insect repellent when outdoors; applying it to exposed skin
  and spraying clothing with repellent.
  
• Wearing long-sleeved shirts and long pants on hikes or other outdoor
  activities when the weather permits.
  
• Keeping window and door screens in good repair so that mosquitoes
  cannot get inside the house.
  
• Covering baby strollers or carriers with mosquito netting when
  taking the baby for a walk outdoors.
• Having pet dogs and cats vaccinated against rabies, and avoiding
  bats, raccoons, and other wild animals that are acting aggressive.
  
• Avoiding sexual contact with people infected by genital herpes.
  Avoiding kissing or sharing drinking glasses with people with cold
  sores.
  
• Having children vaccinated against diseases such as measles and
  mumps.
  
• Seeking prompt medical treatment for any high fever associated
  with an infection.
  

Researchers are working on developing vaccines against West Nile virus
and other mosquito-borne viral infections. As of 2008, the National
Institutes of Health was testing a recently developed vaccine against
equine encephalitis, and a new drug related to acyclovir as a treatment for
HSV encephalitis.