Overview, Causes, & Risk Factors

Encephalitis is an inflammation of the brain.

What is going on in the body?

Encephalitis is usually caused by a viral infection of the braintissue. The infection can also be caused by bacteria, fungi, or parasites.These tiny organisms can enter the brain tissue by any of the following routes:

  • direct infection of the cells in the brain, often following ahead injury
  • through the bloodstream after a bite from a tick or mosquito
  • through the respiratory or gastrointestinal tracts. They then travelthrough the bloodstream and invade the brain.
  • traveling up nerves to the brain. This happens with a dormant herpesinfection or after a bite from an animal withrabies.
  • What are the causes and risks of the condition?

    Most cases of encephalitis are caused by a viral infection of thebrain tissue. Viruses that commonly cause encephalitis include the following:

  • adenovirus, which also causes respiratory infections
  • Borrelia burgdorferi, which also causesBorrelia burgdorferi.\ It is passed to humans through tick bites. Lyme disease
  • Colorado tick virus, which also causes Colorado tick fever
  • cytomegalovirus,which also causes a common childhood infection with mild or vague symptoms
  • enteroviruses, a group of viruses that also causepoliomyelitis andupper respiratory infections
  • Epstein-Barr virus, which also causesmononucleosis
  • herpes simplex viruses, a group of viruses that also causecold sores andgenital herpes
  • La Crosse encephalitis virus
  • measles virus, which also causes measles
  • rubella virus, which also causes German measles
  • St. Louis encephalitis virus
  • varicella zoster viruses, which also causeshingles andchickenpox
  • Western and Eastern equine encephalitis virus
  • West Nile virus
  • Bacteria that can cause encephalitis include the following:

  • leptospirosis, which also causes a flu-like illness
  • mycobacteria, a group of bacteria that also cause tuberculosis
  • mycoplasma, which also cause pneumonia
  • rickettsia, a group of bacteria that also causeRocky Mountain spotted fever
  • West Nile virus,which also causes a flu-like illness
  • Other less-common causes of encephalitis include the following:

  • drug reactions
  • infections with fungi, such as histoplasma and cryptococcus
  • infections with parasites such as those that causemalaria
  • vasculitis, which is an inflammation of the blood vessels that supply the brain
  • People at high risk for encephalitis include those whose age is very young orvery old, and those who have compromised immune systems.

    Symptoms & Signs

    What are the signs and symptoms of the condition?

    Symptoms of encephalitis include the following:

  • confusion
  • drowsiness
  • headache
  • irritability
  • light sensitivity
  • loss of consciousness
  • memory loss
  • muscle weakness
  • poor judgment
  • seizures
  • stiff neck and back
  • sudden fever
  • sudden severe dementia
  • tremors
  • unstable walking
  • vomiting
  • Diagnosis & Tests

    How is the condition diagnosed?

    Diagnosis of encephalitis begins with a medical history andphysical examination. A spinal tap may be done to obtain a sample of thefluid that bathes the brain and spinal cord. The doctor mayorder other tests, including:

  • antibody titer blood teststo detect antibodies to certain organisms
  • blood cultures todetect organisms in the blood
  • cranial CT scan
  • cranial MRI
  • electroencephalogram, also called EEG,which shows brain waves
  • polymerase chain reaction, a blood test that identifies organisms by theirgenes
  • Prevention & Expectations

    What can be done to prevent the condition?

    There are a few ways to prevent encephalitis.Diseases such as polio and measles can be prevented by vaccination.Avoiding ticks and controlling mosquitoes can help prevent the illnessescarried by them. Certain antibiotics, like chloroquine, can help prevent malaria.

    What are the long-term effects of the condition?

    Brain damage is a possible long-term effect of encephalitis.Some individuals will have permanent disability.

    What are the risks to others?

    Some of the organisms that cause encephalitis can spreadfrom person to person.

    Treatment & Monitoring

    What are the treatments for the condition?

    Treatment options vary, depending on what causesthe encephalitis. Medicines used to treat encephalitis include the following:

  • acetaminophen or ibuprofen for headacheand fever
  • antibiotics for infections caused by bacteria
  • anticonvulsants to treat seizures
  • antiviral medicines for infections caused by a virus
  • corticosteroids to reduce brain swelling
  • sedatives for irritability
  • People who develop severe and permanent disabilities may bereferred to a rehabilitation program once their condition is stable.

    What are the side effects of the treatments?

    Many of the medicines used to treat encephalitis may causestomach upset or allergic reactions.Anticonvulsants may cause drowsiness.

    What happens after treatment for the condition?

    Some people with encephalitis have a mild infection thatresolves with effective treatment. Others may have a serious infectionleading to permanent disability or death.

    How is the condition monitored?

    Regular visits to the doctor will be used tomonitor recovery from encephalitis. Any new or worsening symptomsshould be reported to the doctor.

    Article type: xmedgeneral