Encephalitis

What is encephalitis?

Encephalitis is an inflammation of the brain. When the brain becomes inflamed—swollen and irritated—normal blood flow to the brain is altered, leading to symptoms such as confusion, fever, and severe headache. Encephalitis is rare.

What causes encephalitis?

Viral infections are the main cause of encephalitis. A common cause in the United States is the herpes simplex virus, the same virus that causes cold sores and genital herpes. The mumps, measles, chickenpox, mononucleosis (Epstein-Barr virus), influenza, and German measles (rubella) viruses are other common causes of encephalitis. These viruses only rarely infect the brain and cause encephalitis.

Another group of viruses, called arboviruses, can spread encephalitis mainly through bites from mosquitoes and ticks. Most people who are bitten by infected mosquitoes or ticks do not develop any symptoms, and only a very small number of people who develop symptoms of infection from arboviruses actually develop encephalitis. In the U.S., encephalitis caused by arboviruses tends to occur in the spring, summer, and early fall, when mosquitoes and ticks are biting and people are spending more time outdoors.

Although very rare, infection with the rabies virus can also lead to encephalitis that is almost always fatal if not treated before symptoms develop.

What are the symptoms?

The most common symptoms of encephalitis are fever, severe headache, and confusion. Other symptoms may develop, such as sensitivity to light, nausea and vomiting, stiff neck and back, and drowsiness. It is also possible to develop severe symptoms, such as seizures, tremors, personality changes, and even coma.

In general, symptoms that develop suddenly and are severe from the start usually indicate more serious, life-threatening encephalitis.

Early on, symptoms of encephalitis may be similar to those of meningitis, a serious viral or bacterial illness that causes inflammation of the tissues surrounding the brain and spinal cord.

How is encephalitis diagnosed?

Encephalitis is usually diagnosed by analyzing the fluid in the spine (cerebrospinal fluid) for evidence of infection, such as increases in white blood cells and protein. Samples of spinal fluid are taken during a lumbar puncture (also known as a spinal tap), in which a needle is inserted in the lower back between the bones of the spine.

Magnetic resonance imaging (MRI), which takes pictures of the structures inside the body, may reveal bleeding, inflammation, or other changes in certain areas of the brain, depending on what type of encephalitis you have.

An electroencephalogram (EEG), which uses small sensors (electrodes) to measure the electrical impulses in the brain, may show an abnormal change in the brain's electrical activity related to encephalitis.

Blood tests also may be used to identify the virus causing encephalitis.

Less commonly done is a brain biopsy to look for signs of infection.

How is it treated?

In the initial stage of the illness, you likely will be treated in a hospital's intensive care unit. During your stay, your treatment and supportive care will depend upon your particular symptoms and the cause of your illness. If the herpes simplex virus or chickenpox (varicella-zoster) virus is the cause, you will be given the antiviral medication acyclovir in a vein (intravenous, or IV). The success of this treatment depends on giving acyclovir as soon as encephalitis is suspected. Some health professionals also are using the herpes zoster medication valacyclovir for herpes simplex encephalitis, even though it has not yet officially been approved for the treatment of encephalitis (unlabeled use).

No antiviral medication is available to treat encephalitis caused by viruses spread by mosquitoes or ticks. Instead, health professionals provide supportive care to reduce symptoms and allow the body to heal on its own. Such treatment may involve medications to reduce pain and fever or stop seizures. In some cases, you may need a machine (ventilator) to help you breathe.

Frequently Asked Questions

It is important to seek immediate medical attention if you suspect that you have encephalitis. The key symptoms are fever, severe headache, and confusion.

Other symptoms that may occur include:

• Abnormal sensitivity to light (photosensitivity).
• Nausea and vomiting.
• Stiff neck and back.
• Lack of energy, sluggishness (lethargy).
• Drowsiness.

More serious symptoms can also develop, including:

• Seizures or tremors.
• Personality changes.
• Memory loss.
• Trouble learning and understanding.
• Restlessness.
• Confused speech.
• Hallucinations, which is seeing or hearing things that aren't there.
• Delirium, which is a sudden change in your mental status, leading to confusion and unusual behavior.

The most severe form of encephalitis can lead to coma and even death, especially if left untreated. In general, symptoms that develop suddenly and are severe from the start are more likely to progress to a life-threatening case of encephalitis.

Although complications such as speech or memory problems can occur, most people fully recover from encephalitis when treated promptly. However, your chances for a full recovery decrease if you have severe symptoms, such as seizures or coma, or if you delay treatment.¹

The early stage of encephalitis may cause symptoms similar to meningitis, a serious viral or bacterial illness that causes inflammation of the tissues that surround the brain and spinal cord.

Your doctor will ask questions about your medical history and your symptoms. It is important to tell your doctor if you have taken any recent trips or have been sick lately. Your doctor may also ask about your sexual history to see if it's possible that you have had herpes simplex virus.

If your doctor thinks that you may have encephalitis, lab tests usually will be done to confirm the diagnosis.

Spinal fluid analysis

An analysis of the fluid in the spine (cerebrospinal fluid) is one of the most important tests in diagnosing encephalitis. Samples are taken during a lumbar puncture (spinal tap), in which a needle is inserted in the lower back between the bones of the spine. The spinal fluid is examined for evidence of infection, such as increases in white blood cells and protein. In the case of herpes simplex encephalitis, health professionals can test for traces of the virus's genetic material. Also, your doctor may do a viral culture to identify the virus causing encephalitis. For a viral culture, a small amount of the fluid is placed in a container with other cells that grow a virus. It may take several weeks before the results of a viral culture are known.

Imaging tests

Magnetic resonance imaging (MRI) of the head may be used to detect specific areas of inflammation or bleeding in the brain caused by encephalitis. However, most people with encephalitis have normal MRIs.

Another imaging test, computed tomography (CT) scan of the head and face, also may be used to see these changes in the brain. A CT scan uses X-rays to take pictures of the brain. See an illustration of a CT scan of encephalitis .

Blood tests

Testing for antibodies in the blood can identify some causes of encephalitis, including mosquito-borne viruses and the viruses that cause mononucleosis (Epstein-Barr virus), cytomegalovirus, and toxoplasmosis.

Electroencephalogram (EEG)

An electroencephalogram (EEG) can help confirm a diagnosis of encephalitis. An EEG records electrical activity in the brain through wires (electrodes) taped to your head and hooked up to a computer. If you have encephalitis, the EEG may show an abnormal increase or decrease in electrical activity; however, an EEG does not indicate whether the abnormal electrical activity is caused by encephalitis.

Brain biopsy

Brain biopsy sometimes may be used to find the cause of encephalitis, especially if herpes simplex encephalitis is suspected and you do not appear to be improving after treatment with acyclovir (an antiviral medication used to treat the herpes simplex virus). An MRI may also help guide the doctor in determining which tissue to biopsy should a biopsy be needed. Using MRI to guide the biopsy needle, the doctor removes a small sample of brain tissue and examines it for viral infection. Brain biopsy is seldom used because tests of blood and spinal fluid usually can accurately diagnose encephalitis caused by the herpes simplex virus.

You may be treated for encephalitis in a hospital's intensive care unit. During your stay, your vital signs (blood pressure, heart rate, breathing, and level of body fluids) will be closely monitored. Treatment will depend on your symptoms and the particular cause of encephalitis, if the cause can be determined.

Encephalitis caused by the herpes simplex virus or the chickenpox (varicella-zoster) virus is treated with the antiviral medication acyclovir, which is given in a vein (intravenous, or IV).¹ It is important to start acyclovir treatment as soon as encephalitis is suspected, even if the exact cause of the illness is not known. This is because early treatment makes it more likely that you will get better.

Call your doctor immediately if you think you have symptoms of encephalitis, such as a sudden and severe headache, fever, and confusion, especially if you also have a stiff neck, nausea, vomiting, and drowsiness. Treatment works best when given early in the illness.

Some health professionals also are using the herpes zoster (shingles) medication valacyclovir for herpes simplex encephalitis, even though this medication has not officially been approved for the treatment of encephalitis (unlabeled use).

Encephalitis caused by arboviruses, which are carried by mosquitoes and ticks, will not respond to acyclovir or other medications. Instead of trying to kill the virus, doctors treat the symptoms so that you are comfortable and the body can heal itself.

• High fever may be reduced with acetaminophen (Tylenol) or nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, aspirin, or naproxen. However, a mild fever may actually promote healing and is usually not treated. Aspirin should not be given to anyone younger than 20 because of the risk of Reye's syndrome.
• Seizures may be controlled with anticonvulsant medications such as phenytoin (Dilantin) or phenobarbital.
• A machine to help you breathe (ventilator) and other supportive measures may be needed if you go into a coma.

Because encephalitis can be a life-threatening condition, it is not appropriate to treat it at home. Symptoms such as high fever, severe headache, and confusion along with nausea and vomiting and possibly a stiff neck and back may be caused by encephalitis. If you think you or someone you know may have encephalitis, seek immediate medical attention.

Once you have been released from the hospital or are under the care of your doctor, it may take several weeks or months to fully recover from your symptoms. You can do things at home to help yourself feel better.

• Get good nutrition and plenty of rest to help your body heal.
• Follow your doctor's instructions on drinking fluids; sometimes, too much fluid can cause more swelling in the brain and make symptoms of encephalitis worse.
• Take nonprescription pain relievers, such as acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs) such as naproxen, ibuprofen, or aspirin, for headaches unless your doctor has prescribed another pain reliever. Do not give aspirin to anyone younger than 20 because of the risk of Reye's syndrome.
• Keep the lights low if you are sensitive to light.
• Try to be patient while you are recovering—it may take several weeks or months to fully recover from all of your symptoms. Most people with encephalitis make a full recovery.

If you have muscle weakness or problems with coordination as a result of encephalitis, your doctor may prescribe physical therapy and range-of-motion exercises. Likewise, if you have continued problems with speech or memory loss, your doctor may order speech and occupational therapies.

It is, of course, best if you can prevent encephalitis from ever occurring. You can decrease your risk of getting encephalitis by taking the following steps:

• Make sure you are vaccinated against measles, mumps, rubella, chickenpox, and influenza. Encephalitis is a rare complication of these diseases.
• Avoid areas where there has been an outbreak of viral encephalitis. If you cannot avoid these areas, you can reduce your risk of mosquito bites.
  • Stay indoors at dawn and dusk and in the early evening, when mosquitoes are most active.
  • Wear long-sleeved shirts and long pants when you go outdoors.
  • Avoid wearing floral fragrances from perfumes, soaps, hair care products, and lotions. These may attract mosquitoes.
  • Spray clothing with an insect repellent containing permethrin or DEET (N,N-diethyl-meta-toluamide) to prevent mosquitoes from biting through clothing. Apply insect repellent sparingly to exposed skin. An effective repellent will contain 35% DEET; concentrations greater than 50% do not provide any additional protection.
  • Avoid applying repellent to the hands of children. Repellents may irritate the eyes and mouth.
• Do not use old tires as swings or play equipment or keep them on your property for other reasons. When old tires collect water, they become excellent breeding grounds for mosquitoes.

Vaccines are available for certain types of mosquito- and tick-borne encephalitis that occur in the Far East and in central and eastern Europe. Japanese encephalitis virus may be prevented by taking three doses of a vaccine.^{2, 1} If you are planning an extended visit to one of these areas, especially if you will be spending time in rural areas, you may want to be vaccinated against the type of encephalitis that is widespread in that area.

No human vaccine is available yet for any of the types of mosquito-borne encephalitis that occur in the United States.

Online Resource

Organization

• Headaches
• Meningitis
• West Nile Virus

Citations

1. Roos KL (2003). Encephalitis. In RW Evans, ed., Saunders Manual of Neurologic Practice, pp. 711–713. Philadelphia: Saunders.

2. Kirkpatric BD, Alston WK (2003). Current immunizations for travel. Current Opinion in Infectious Diseases, 16: 369–374.

Other Works Consulted

• Drugs for non-HIV viral infections (2005). Treatment Guidelines from the Medical Letter, 3(32): 23–32.

• Gilden DH (2006). Acute viral central nervous system diseases. In DC Dale, DD Federman, eds., ACP Medicine, section 11, chap. 16. New York: WebMD.

• Griffin DE (2005). Encephalitis, myelitis, and neuritis. In GL Mandell et al., eds., Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 6th ed., vol. 1, pp. 1143–1150. Philadelphia: Elsevier Churchill Livingstone.

• Romero JR, Newland JG (2003). Viral meningitis and encephalitis: Traditional and emerging viral agents. Seminars in Pediatric Infectious Diseases, 14(2): 72–82.

Author:	Amy Fackler, MA Debby Golonka, MPH	Last Updated August 17, 2006
Medical Review:	Adam Husney, MD - Family Medicine W. David Colby, MSc, MD, FRCPC - Infectious Disease
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