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Encephalitis is an inflammation of the brain. It usually follows or results from an infection.

What is going on in the body? 
Bacteria, viruses, fungi or parasites can cause encephalitis. A drug reaction or a non-infectious disease like vasculitis (inflammation of the blood vessels) can also lead to encephalitis. Viruses, often the enteroviruses (a family of viruses), are the most common cause of the condition. Organisms can get into the central nervous system by several routes. Commonly, they enter the body through the respiratory or gastrointestinal tracts. They then travel through the bloodstream and invade the brain. Some organisms, such as the one that causes Rocky Mountain spotted fever, enter the bloodstream through the bite of a tick or other arthropod. Other organisms gain access to the brain by travelling up nerves. One example of such an organism is the rabies virus. The symptoms of encephalitis can be due to direct infection of the cells in the brain. They can also be caused by the attempts of the immune system (the body's defence system) to fight the infection.

What are the signs and symptoms of the condition? 
  • confusion
  • lethargy, coma
  • fever
  • seizure
  • headache

What are the causes and risks of the condition? 
  • viruses: enteroviruses, herpes simplex virus, varicella-zoster virus, Epstein-Barr virus, cytomegalovirus, adenovirus, rubella and measles.
  • bacteria: listeria, tuberculosis, brucella, mycoplasma, leptospirosis, Lyme disease, etc.
  • fungi: cryptococcus, histoplasma, etc.
  • parasites: malaria, acanthamoeba, etc.
What can be done to prevent the condition? 
There are a few ways to prevent development of encephalitis. Contracting polio, which is associated with encephalitis, can be prevented by vaccination. Avoiding ticks and controlling mosquitos can help prevent the illnesses carried by them. Certain antibiotics, like chloroquine, can help prevent malaria.

How is the condition diagnosed? 
Diagnosis is usually based on the symptoms, the findings in the cerebrospinal fluid (CSF) (clear fluid surrounding the brain and spinal cord), and findings on imaging of the brain, such as magnetic resonance imaging (MRI) (special three-dimensional image using magnets) or computed tomography (CT) scan (special three-dimensional xray). Electroencephalography (EEG) (recording of brain waves) can sometimes be helpful. Some of the organisms can be seen with a microscope, or cultured from the CSF. Finding antibodies to the organisms in the blood or CSF can identify many of the organisms causing the brain swelling. Polymerase chain reaction (test that identifies organisms by their genes) can also be used to detect many of these organisms.

What are the long-term effects of the condition? 
Brain damage is a possible long-term effect of encephalitis.

What are the risks to others? 
Some of the organisms that cause encephalitis can spread from person to person.

What are the treatments for the condition? 
Treatment depends on which organism is causing the encephalitis. For those that are treatable, therapy must be begun quickly.

Author: Danielle Zerr, MD
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Potential conflict of interest information for reviewers available on request

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