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Encephalitis

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 brain tissue. 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 a head injury

through the bloodstream after a bite from a tick or mosquito

through the respiratory or gastrointestinal tracts. They then travel through the bloodstream and invade the brain.

traveling up nerves to the brain. This happens with a dormant herpes infection or after a bite from an animal with rabies.

What are the causes and risks of the condition?

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

adenovirus, which also causes respiratory infections

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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 cause poliomyelitis and upper respiratory infections

Epstein-Barr virus, which also causes mononucleosis

herpes simplex viruses, a group of viruses that also cause cold sores and genital 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 cause shingles and chickenpox

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 cause Rocky 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 cause malaria

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 or very 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 and physical examination. A spinal tap may be done to obtain a sample of the fluid that bathes the brain and spinal cord. The doctor may order other tests, including:

antibody titer blood tests to detect antibodies to certain organisms

blood cultures to detect 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 their genes

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 illnesses carried 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 spread from person to person.

Treatment & Monitoring

What are the treatments for the condition?

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

acetaminophen or ibuprofen for headache and 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 be referred 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 cause stomach upset or allergic reactions. Anticonvulsants may cause drowsiness.

What happens after treatment for the condition?

Some people with encephalitis have a mild infection that resolves with effective treatment. Others may have a serious infection leading to permanent disability or death.

How is the condition monitored?

Regular visits to the doctor will be used to monitor recovery from encephalitis. Any new or worsening symptoms should be reported to the doctor.

Attribution

Author:Danielle Zerr, MD
Date Written:
Editor:Crist, Gayle P., MS, BA
Edit Date:09/19/02
Reviewer:Kathleen A. MacNaughton, RN, BSN
Date Reviewed:09/18/02