Encephalitis

Definition

Encephalitis is an inflammation of the brain, usually caused by a direct viral infection or a hypersensitivity reaction to a virus or foreign protein. Brain inflammation caused by a bacterial infection is sometimes called cerebritis. When both the brain and spinal cord are involved, the disorder is called encephalomyelitis. An inflammation of the brain's covering, or meninges, is called meningitis .

Description

Encephalitis is an inflammation of the brain. The inflammation is a reaction of the body's immune system to infection or invasion. During the inflammation, the brain's tissues become swollen. The combination of the infection and the immune reaction to it can cause headache and a fever , as well as more severe symptoms in some cases.

The viruses causing primary encephalitis can be epidemic or sporadic. The polio virus is an epidemic cause. Arthropod-borne viral encephalitis is responsible for most epidemic viral encephalitis. The viruses live in animal hosts and mosquitoes that transmit the disease. The most common form of non-epidemic or sporadic encephalitis is caused by the herpes simplex virus, type 1 (HSV-1) and has a high rate of death. Mumps is another example of a sporadic cause.

Demographics

Approximately 2,000 cases of encephalitis are reported to the Centers for Disease Control and Prevention in Atlanta, Georgia, each year. Encephalitis can strike anyone, at any age, although some kinds of encephalitis are more common in children. Other kinds of encephalitis can affect anyone, but may affect children more severely.

Causes and symptoms

There are more than a dozen viruses that can cause encephalitis, spread by either human-to human contact or by animal bites . Encephalitis may occur with several common viral infections of childhood. Viruses and viral diseases that may cause encephalitis include:

• chickenpox
• measles
• mumps
• Epstein-Barr virus (EBV)
• cytomegalovirus infection
• HIV
• herpes simplex
• herpes zoster (shingles)
• herpes B
• polio
• rabies
• mosquito-borne viruses (arboviruses)

Primary encephalitis is caused by direct infection by the virus, while secondary encephalitis is due to a post-infectious immune reaction to viral infection elsewhere in the body. Secondary encephalitis may occur with measles, chickenpox, mumps, rubella , and EBV. In secondary encephalitis, symptoms usually begin five to ten days after the onset of the disease itself and are related to the breakdown of the myelin sheath that covers nerve fibers.

In rare cases, encephalitis may follow vaccination against some of the viral diseases listed above. Creutzfeldt-Jakob disease, a very rare brain disorder caused by an infectious particle called a prion, may also cause encephalitis.

Mosquitoes spread viruses responsible for equine encephalitis (eastern and western types), St. Louis encephalitis, California encephalitis, and Japanese encephalitis. Lyme disease , spread by ticks, can cause encephalitis, as can Colorado tick fever. Rabies is most often spread by animal bites from dogs, cats, mice, raccoons, squirrels, and bats and may cause encephalitis.

Equine encephalitis is carried by mosquitoes that do not normally bite humans but do bite horses and birds. It is occasionally picked up from these animals by mosquitoes that do bite humans. Japanese encephalitis and St. Louis encephalitis are also carried by mosquitoes. The risk of contracting a mosquito-borne virus is greatest in mid- to late summer, when mosquitoes are most active, in those rural areas where these viruses are known to exist. Eastern equine encephalitis occurs in eastern and southeastern United States; western equine and California encephalitis occur throughout the West; and St. Louis encephalitis occurs throughout the country. Japanese encephalitis does not occur in the United States but is found throughout much of Asia. The viruses responsible for these diseases are classified as arbovirus, and these diseases are collectively called arbovirus encephalitis.

Herpes simplex encephalitis, the most common form of sporadic encephalitis in western countries, is a disease with significantly high mortality. It occurs in children and adults and both sides of the brain are affected. It is theorized that brain infection is caused by the virus moving from a peripheral location to the brain via two nerves, the olfactory and the trigeminal (largest nerves in the skull).

Herpes simplex encephalitis is responsible for 10 percent of all encephalitis cases and is the main cause of sporadic, fatal encephalitis. In untreated people, the rate of death is 70 percent while the mortality is 15 to 20 percent in persons who have been treated with acyclovir. The symptoms of herpes simplex encephalitis are fever, rapidly disintegrating mental state, headache, and behavioral changes.

The symptoms of encephalitis range from very mild to very severe and may include:

• headache
• fever
• lethargy (sleepiness, decreased alertness, and fatigue)
• malaise
• nausea and vomiting
• visual disturbances
• tremor
• decreased consciousness (drowsiness, confusion, delirium, and unconsciousness)
• stiff neck
• seizures

Symptoms may progress rapidly, changing from mild to severe within several days or even several hours.

When to call the doctor

A physician should be called whenever a headache does not respond to medication or when a person experiences a fever over 104°F (40.0°C), nausea and vomiting , visual disturbances, a stiff neck, or seizures.

A doctor should be called when an infant's temperature rises above 100°F (37.8°C) and cannot be brought down within a few minutes. Infants whose temperatures exceed 102°F (38.9°C) should be sponge-bathed in cool water while waiting for emergency help to arrive.

Diagnosis

Diagnosis of encephalitis includes careful questioning to determine possible exposure to viral sources. Tests that can help confirm the diagnosis and rule out other disorders include:

• blood tests (to detect antibodies to viral antigens and foreign proteins)
• cerebrospinal fluid analysis, or spinal tap (to detect viral antigens and provide culture specimens for the virus or bacteria that may be present in the cerebrospinal fluid)
• electroencephalogram (EEG)
• CT and MRI scans

A brain biopsy (surgical gathering of a small tissue sample) may be recommended in some cases in which treatment has thus far been ineffective and the cause of the encephalitis is unclear. Definite diagnosis by biopsy may allow specific treatment that would otherwise be too risky.

Treatment

Choice of treatment for encephalitis depends on the cause. Bacterial encephalitis is treated with antibiotics . Viral encephalitis is usually treated with antiviral drugs , including acyclovir, ganciclovir, foscarnet, ribavirin, and AZT. Viruses that respond to acyclovir include herpes simplex, the most common cause of sporadic (non-epidemic) encephalitis in the United States.

The symptoms of encephalitis may be treated with a number of different drugs. Corticosteroids, including prednisone and dexamethasone, are sometimes prescribed to reduce inflammation and brain swelling. Anticonvulsant drugs, including phenytoin, are used to control seizures. Fever may be reduced with acetaminophen or other fever-reducing drugs.

A person with encephalitis must be monitored carefully, since symptoms may change rapidly. Blood tests may be required regularly to track levels of fluids and salts in the blood.

Prognosis

Encephalitis symptoms may last several weeks. Most cases of encephalitis are mild, and recovery is usually quick. Mild encephalitis usually leaves no residual neurological problems. Overall, approximately 10 percent of those with encephalitis die from their infections or complications such as secondary infection. Some forms of encephalitis have more severe courses, including herpes encephalitis, in which mortality is 15 to 20 percent with treatment, and 70 to 80 percent without. Antiviral treatment is ineffective for eastern equine encephalitis, and mortality is approximately 30 percent.

Permanent neurological consequences may follow recovery in some cases. Consequences may include personality changes, memory loss, language difficulties, seizures, and partial paralysis.

Prevention

Because encephalitis is caused by infection, it may be prevented by avoiding the infection. Minimizing contact with others who have any of the viral illnesses listed above may reduce one's chances of becoming infected. Most infections are spread by hand-to-hand or hand-to-mouth contact; frequent hand washing may reduce the likelihood of infection if contact cannot be avoided.

Mosquito-borne viruses may be avoided by preventing mosquito bites. Mosquitoes are most active at dawn and dusk and are most common in moist areas with standing water. Covering skin and using mosquito repellents on exposed skin can reduce the chances of being bitten.

KEY TERMS

Cerebrospinal fluid analysis —A laboratory test, important in diagnosing diseases of the central nervous system, that examines a sample of the fluid surrounding the brain and spinal cord. The fluid is withdrawn through a needle in a procedure called a lumbar puncture.

Computed tomography (CT) —An imaging technique in which cross-sectional x rays of the body are compiled to create a three-dimensional image of the body's internal structures; also called computed axial tomography.

Electroencephalogram (EEG) —A record of the tiny electrical impulses produced by the brain's activity picked up by electrodes placed on the scalp. By measuring characteristic wave patterns, the EEG can help diagnose certain conditions of the brain.

Inflammation —Pain, redness, swelling, and heat that develop in response to tissue irritation or injury. It usually is caused by the immune system's response to the body's contact with a foreign substance, such as an allergen or pathogen.

Magnetic resonance imaging (MRI) —An imaging technique that uses a large circular magnet and radio waves to generate signals from atoms in the body. These signals are used to construct detailed images of internal body structures and organs, including the brain.

Vaccine —A substance prepared from a weakened or killed microorganism which, when injected, helps the body to form antibodies that will prevent infection by the natural microorganism.

Virus —A small infectious agent consisting of a core of genetic material (DNA or RNA) surrounded by a shell of protein. A virus needs a living cell to reproduce.

Vaccines are available against some viruses, including polio, herpes B, Japanese encephalitis, and equine encephalitis. Rabies vaccine is available for animals; it is also given to people after exposure. Japanese encephalitis vaccine is recommended for those traveling to Asia and staying in affected rural areas during transmission season.

Nutritional concerns

Adequate nutrition and fluids improve the chances for a full recovery from encephalitis.

Parental concerns

Parents should carefully monitor their infants and young children for symptoms of fever. Any fever that exceeds 103°F (39.4°C) for more than a few minutes should be promptly treated. Any complaints of a stiff neck, loss of consciousness, unexplained vomiting, or seizure activity should be promptly brought to competent medical attention.

Resources

BOOKS

Halstead, Scott A. "Arbovirus Encephalitis in North America." In Nelson Textbook of Pediatrics, 17th ed. Edited by Richard E. Behrman et al. Philadelphia: Saunders, 2003, pp. 1086–8.

Johnston, Michael V. "Encephalopathies." In Nelson Textbook of Pediatrics, 17th ed. Edited by Richard E. Behrman et al. Philadelphia: Saunders, 2003, pp. 2023–8.

Nath, Avindra, and Joseph R. Berger. "Acute Viral Meningitis and Encephalitis." In Cecil Textbook of Medicine, 22nd ed. Edited by Lee Goldman, et al. Philadelphia: Saunders, 2003, pp. 2232–5.

Tyler, Kenneth L. "Viral Meningitis and Encephalitis." In Harrison's Principles of Internal Medicine, 15th ed. Edited by Eugene Braunwald et al. New York: McGraw-Hill, 2001, pp. 2471–80.

PERIODICALS

Arciniegas, D. B., and C. A. Anderson. "Viral encephalitis: neuropsychiatric and neurobehavioral aspects." Current Psychiatry Reports 6, no. 5 (2004): 372–9.

Cunha, B. A. "Differential diagnosis of West Nile encephalitis." Current Opinions in Infectious Disease 17, no. 5 (2004): 413–20.

Lyle, P., et al. "Evaluation of encephalitis in the toddler: what part of negative don't you understand?" Current Opinions in Pediatrics 16, no. 5 (2004): 567–70.

Morgan, R. "West Nile viral encephalitis: a case study." Journal of Neuroscience of Nursing 36, no. 4 (2004): 185–8.

Savas, L., et al. "Full recovered meningoencephalomyelitis caused by mumps virus." European Journal of Neurology 11, no. 9 (2004): 639–40.

ORGANIZATIONS

American Academy of Neurology. 1080 Montreal Avenue, St. Paul, MN 55116. Web site: <www.aan.com>.

American Academy of Pediatrics. 141 Northwest Point Blvd., Elk Grove Village, IL 60007–1098. Web site: <www.aap.org/>.

American College of Emergency Physicians. PO Box 619911, Dallas, TX 75261-9911. Web site: <www.acep.org/>.

WEB SITES

"Arboviral Encephalitides." Centers for Disease Control and Prevention. Available online at <www.cdc.gov/ncidod/dvbid/arbor/> (accessed January 5, 2005).

"Encephalitis." Mayo Clinic. Available online at <www.mayoclinic.com/invoke.cfm?id=DS00226> (accessed January 5, 2005).

"Encephalitis." MedlinePlus. Available online at <www.nlm.nih.gov/medlineplus/encephalitis.html> (accessed January 5, 2005).

"Encephalitis." World Health Organization. Available online at <www.who.int/topics/encephalitis/en/> (accessed January 5, 2005).

Encephalitis Information Resource. Available online at <www.encephalitis.info/> (accessed January 5, 2005).

"NINDS Encephalitis and Meningitis Information Page." National Institute of Neurological Disorders and Stroke. Available online at <www.ninds.nih.gov/health_and_medical/disorders/encmenin_doc.htm> (accessed January 5, 2005).

L. Fleming Fallon, Jr., MD, DrPH

Encephalitis

Definition

Encephalitis is an inflammation of the brain, usually caused by a direct viral infection or a hyper-sensitivity reaction to a virus or foreign protein. Brain inflammation caused by a bacterial infection is sometimes called cerebritis. When both the brain and spinal cord are involved, the disorder is called encephalomyelitis. An inflammation of the brain's covering, or meninges, is called meningitis.

Description

Encephalitis is an inflammation of the brain. The inflammation is a reaction of the body's immune system to infection or invasion. During the inflammation, the brain's tissues become swollen. The combination of the infection and the immune reaction to it can cause headache and a fever, as well as more severe symptoms in some cases.

Approximately 2,000 cases of encephalitis are reported to the Centers for Disease Control in Atlanta, GA each year. The viruses causing primary encephalitis can be epidemic or sporadic. The polio virus is an epidemic cause. Arthropod-borne viral encephalitis is responsible for most epidemic viral encephalitis. The viruses live in animal hosts and mosquitos that transmit the disease. The most common form of non-epidemic or sporadic encephalitis is caused by the herpes simplex virus, type 1 (HSV-1) and has a high rate of death. Mumps is another example of a sporadic cause.

Causes and symptoms

Causes

There are more than a dozen viruses that can cause encephalitis, spread by either human-to human contact or by animal bites. Encephalitis may occur with several common viral infections of childhood. Viruses and viral diseases that may cause encephalitis include:

• chickenpox
• measles
• mumps
• Epstein-Barr virus (EBV)
• cytomegalovirus infection
• HIV
• herpes simplex
• herpes zoster (shingles )
• herpes B
• polio
• rabies
• mosquito-borne viruses (arboviruses)

Primary encephalitis is caused by direct infection by the virus, while secondary encephalitis is due to a post-infectious immune reaction to viral infection elsewhere in the body. Secondary encephalitis may occur with measles, chickenpox, mumps, rubella, and EBV. In secondary encephalitis, symptoms usually begin five to 10 days after the onset of the disease itself and are related to the breakdown of the myelin sheath that covers nerve fibers.

In rare cases, encephalitis may follow vaccination against some of the viral diseases listed above. Creutzfeldt-Jakob disease, a very rare brain disorder caused by an infectious particle called a prion, may also cause encephalitis.

Mosquitoes spread viruses responsible for equine encephalitis (eastern and western types), St. Louis encephalitis, California encephalitis, and Japanese encephalitis. Lyme disease, spread by ticks, can cause encephalitis, as can Colorado tick fever. Rabies is most often spread by animal bites from dogs, cats, mice, raccoons, squirrels, and bats and may cause encephalitis.

Equine encephalitis is carried by mosquitoes that do not normally bite humans but do bite horses and birds. It is occasionally picked up from these animals by mosquitoes that do bite humans. Japanese encephalitis and St. Louis encephalitis are also carried by mosquitoes. The risk of contracting a mosquito-borne virus is greatest in mid- to late summer, when mosquitoes are most active, in those rural areas where these viruses are known to exist. Eastern equine encephalitis occurs in eastern and southeastern United States; western equine and California encephalitis occur throughout the West; and St. Louis encephalitis occurs throughout the country. Japanese encephalitis does not occur in the United States, but is found throughout much of Asia. The viruses responsible for these diseases are classified as arbovirus and these diseases are collectively called arbovirus encephalitis.

Herpes simplex encephalitis, the most common form of sporadic encephalitis in western countries, is a disease with significantly high mortality. It occurs in children and adults and both sides of the brain are affected. It is theorized that brain infection is caused by the virus moving from a peripheral location to the brain via two nerves, the olfactory and the trigeminal (largest nerves in the skull).

Herpes simplex encephalitis is responsible for 10% of all encephalitis cases and is the main cause of sporadic, fatal encephalitis. In untreated patients, the rate of death is 70% while the mortality is 15-20% in patients who have been treated with acyclovir. The symptoms of herpes simplex encephalitis are fever, rapidly disintegrating mental state, headache, and behavioral changes.

Symptoms

The symptoms of encephalitis range from very mild to very severe and may include:

• headache
• fever
• lethargy (sleepiness, decreased alertness, and fatigue)
• malaise
• nausea and vomiting
• visual disturbances
• tremor
• decreased consciousness (drowsiness, confusion, delirium, and unconsciousness)
• stiff neck
• seizures

Symptoms may progress rapidly, changing from mild to severe within several days or even several hours.

Diagnosis

Diagnosis of encephalitis includes careful questioning to determine possible exposure to viral sources. Tests that can help confirm the diagnosis and rule out other disorders include:

• Blood tests. These are to detect antibodies to viral antigens, and foreign proteins.
• Cerebrospinal fluid analysis (spinal tap). This detects viral antigens, and provides culture specimens for the virus or bacteria that may be present in the cerebrospinal fluid.
• Electroencephalogram (EEG).
• CT and MRI scans.

A brain biopsy (surgical gathering of a small tissue sample) may be recommended in some cases where treatment to date has been ineffective and the cause of the encephalitis is unclear. Definite diagnosis by biopsy may allow specific treatment that would otherwise be too risky.

Treatment

Choice of treatment for encephalitis will depend on the cause. Bacterial encephalitis is treated with antibiotics. Viral encephalitis is usually treated with antiviral drugs including acyclovir, ganciclovir, foscarnet, ribovarin, and AZT. Viruses that respond to acyclovir include herpes simplex, the most common cause of sporadic (non-epidemic) encephalitis in the United States.

The symptoms of encephalitis may be treated with a number of different drugs. Corticosteroids, including prednisone and dexamethasone, are sometimes prescribed to reduce inflammation and brain swelling. Anticonvulsant drugs, including dilantin and phenytoin, are used to control seizures. Fever may be reduced with acetaminophen or other fever-reducing drugs.

A person with encephalitis must be monitored carefully, since symptoms may change rapidly. Blood tests may be required regularly to track levels of fluids and salts in the blood.

Prognosis

Encephalitis symptoms may last several weeks. Most cases of encephalitis are mild, and recovery is usually quick. Mild encephalitis usually leaves no residual neurological problems. Overall, approximately 10% of those with encephalitis die from their infections or complications such as secondary infection. Some forms of encephalitis have more severe courses, including herpes encephalitis, in which mortality is 15-20% with treatment, and 70-80% without. Antiviral treatment is ineffective for eastern equine encephalitis, and mortality is approximately 30%.

Permanent neurological consequences may follow recovery in some cases. Consequences may include personality changes, memory loss, language difficulties, seizures, and partial paralysis.

Prevention

Because encephalitis is due to infection, it may be prevented by avoiding the infection. Minimizing contact with others who have any of the viral illness listed above may reduce the chances of becoming infected. Most infections are spread by hand-to-hand or hand-to-mouth contact; frequent hand washing may reduce the likelihood of infection if contact cannot be avoided.

Mosquito-borne viruses may be avoided by preventing mosquito bites. Mosquitoes are most active at dawn and dusk, and are most common in moist areas with standing water. Minimizing exposed skin and use of mosquito repellents on other areas can reduce the chances of being bitten.

Vaccines are available against some viruses, including polio, herpes B, Japanese encephalitis, and equine encephalitis. Rabies vaccine is available for animals; it is also given to people after exposure. Japanese encephalitis vaccine is recommended for those traveling to Asia and staying in affected rural areas during transmission season.

Resources

ORGANIZATIONS

Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. 〈http://www.cdc.gov〉.

KEY TERMS

Cerebrospinal fluid analysis— A analysis that is important in diagnosing diseases of the central nervous system. The fluid within the spine will indicate the presence of viruses, bacteria, and blood. Infections such as encephalitis will be indicated by an increase of cell count and total protein in the fluid.

Computerized tomography (CT) Scan— A test to examine organs within the body and detect evidence of tumors, blood clots, and accumulation of fluids.

Electroencephalagram (EEG)— A chart of the brain waves picked up by the electrodes placed on the scalp. Changes in brain wave activity can be an indication of nervous system disorders.

Inflammation— A response from the immune system to an injury. The signs are redness, heat, swelling, and pain.

Magnetic Resonance Imaging (MRI)— MRI is diagnostic radiography using electromagnetic energy to create an image of the central nervous system (CNS), blood system, and musculoskeletal system.

Vaccine— A prepartation containing killed or weakened microorganisms used to build immunity against infection from that microorganism.

Virus— A very small organism that can only live within a cell. They are unable to reproduce outside that cell.

encephalitis , general term used to describe a diffuse inflammation of the brain and spinal cord, usually of viral origin, often transmitted by mosquitoes, in contrast to a bacterial infection of the meninges (membrane surrounding the brain and spinal cord), known as meningitis . Diagnostic symptoms include capillary congestion, small hemorrhages into perivascular spaces, accumulation of plasma cells and lymphocytes, and increased pressure and protein content of cerebrospinal fluid.

Among the several forms of viral brain inflammation are rabies, polio, and two types transmitted by the mosquito: equine encephalitis in its various forms and St. Louis encephalitis. The latter two have appeared in epidemic form in the United States and are characterized by high fever, prolonged coma (which is responsible for the disease being known as a "sleeping sickness" ; see also trypanosomiasis ), and convulsions sometimes followed by death. Encephalitis that results as a complication of another systemic infection is known as parainfectious encephalitis and can follow such diseases as measles (rubeola), influenza, and scarlet fever. The AIDS virus also infects the brain and produces dementia in a predictably progressive pattern. Although no specific treatment can destroy the virus once the disease has become established, many types of encephalitis can be prevented by immunization.

ENCEPHALITIS

DEFINITION

Encephalitis (pronounced in-seh-fuh-LIE-tess) is an inflammation of the brain. It may be caused by a number of different factors. One of the most common causes is direct infection of the brain by a virus or bacterium. Inflammation can also occur as a complication of some other disorder, such as mumps (see mumps entry) or herpes simplex (see herpes infections entry). About two thousand cases of encephalitis are reported in the United States each year.

DESCRIPTION

Inflammation of the brain is a reaction of the body's immune system. The immune system is a network of cells, tissues, and chemical substances designed to protect the body against invasion by foreign agents. Sometimes, a foreign agent gets directly into the brain. In the process of fighting off the foreign agent, brain tissues become swollen and inflamed. In other cases, the infection occurs elsewhere in the body, such as the throat or neck. The immune reaction to those infections can also cause inflammation of the brain.

CAUSES

There are more than a dozen viruses that can cause encephalitis. In some cases, the viruses are spread by direct contact between two people. In other cases, the viruses are transmitted by means of an animal or insect bite. Some common viruses and viral diseases that can cause encephalitis include:

• Chickenpox (see chickenpox entry)
• Measles (see measles entry)
• Mumps
• Epstein-Barr virus
• Cytomegalovirus infection (EBV)
• Human immunodeficiency virus (HIV; see AIDS entry)
• Herpes simplex virus
• Herpes zoster virus (shingles)
• Herpes B virus
• Polio (see polio entry)
• Rabies (see rabies entry)
• Viruses carried by mosquitoes (arboviruses)

Some of these viruses may infect the brain directly. In other cases, the infection spreads from another part of the body, as is usually the case with chickenpox, measles, mumps, rubella (see rubella entry), and Epstein-Barr virus. For example, a person may develop a case of chickenpox, then about five to ten days later, as an immune reaction to the chickenpox virus, the brain becomes inflamed and swollen.

Many forms of encephalitis are spread by the bites of insects or animals. Mosquitoes are common carriers of encephalitis viruses. They carry the viruses in their blood and saliva. When they bite a human, they may transfer the virus to the human's bloodstream. The virus multiplies and spreads throughout the body. When it reaches the brain, it may cause encephalitis.

Dogs, cats, mice, raccoons, squirrels, and bats are also carriers of encephalitis viruses. These animals also carry the virus in their blood and saliva. When they bite a human, they can transmit the virus to the human bloodstream.

Encephalitis: Words to Know

Cerebrospinal fluid:

Fluid found within the spinal column that is often used to diagnose infections of the central nervous system (the brain and spinal cord).

Electroencephalogram (EEG):

A test in which electrical currents in the brain are measured to see if there has been damage to the brain.

Inflammation:

A response by the immune system to invasion by a foreign body; signs of an inflammation are redness, heat, swelling, and pain.

Magnetic resonance imaging (MRI):

A technique for studying the structure of internal organs by using magnetic waves.

Vaccine:

A preparation containing dead or weakened viruses or bacteria to increase a person's immunity (protection) against a certain type of infection.

Virus:

A very small organism that can live only within a cell and that can cause some form of disease.

One of the most serious forms of encephalitis is caused by the herpes simplex virus. The herpes simplex virus causes cold sores and genital herpes. Sometimes the herpes virus spreads directly to the brain, causing an encephalitis infection. About 10 percent of all encephalitis cases are caused by this virus. In untreated patients, the rate of death is 70 percent. The rate drops to 15 to 20 percent if patients receive treatment.

SYMPTOMS

The symptoms of encephalitis range from very mild to very severe. They include:

• Headache
• Fever
• Lethargy (sleepiness and fatigue)
• Malaise (a feeling of weakness and poor health)
• Nausea and vomiting
• Visual problems
• Tremor (shaking)
• Decreased consciousness (drowsiness and confusion)
• Stiff neck
• Seizures

Symptoms often progress rapidly. They change from being mild to severe within several days or even a few hours.

DIAGNOSIS

The first step in diagnosis may be a medical history. A doctor will try to determine if the patient has had recent contact with a virus that can cause encephalitis. The diagnosis can be confirmed with a variety of tests. These include:

• Blood tests. Blood tests may detect antibodies against viruses. Antibodies are chemicals produced by the body's immune system. They are manufactured when a foreign agent, such as a virus, enters the body.
• Lumbar puncture (spinal tap). In a lumbar puncture, a long, thin needle is inserted into the spinal column. A small amount of cerebrospinal (pronounced suh-REE-bro-spyn-al) fluid (CSF) is removed. The fluid can be tested to see if viruses or bacteria are present.
• Electroencephalogram (pronounced ih-LEK-tro-en-SEF-ah-lo-gram; also called an EEG). An EEG is a test in which electrical currents in the brain are measured. The test can show whether there has been damage to the brain.
• Imaging scans. The brain can be studied by a number of imaging techniques, such as X rays and magnetic resonance imaging (MRI). These techniques often reveal abnormal structures in the brain.
• Biopsy. In a biopsy, a needle is used to remove a small portion of brain tissue. The brain tissue can then be studied under a microscope. The presence of viruses or other foreign agents may be detected.

TREATMENT

The treatment used for encephalitis depends on the cause of the infection. Bacterial encephalitis can be treated with antibiotics. Antibiotics kill bacteria, but not viruses. Viral encephalitis can be treated with drugs that kill viruses. Relatively few drugs of this kind have been developed. Some antivirals that can be used are acyclovir (pronounced a-SIGH-klo-veer), ganciclovir (pronounced gan-SIGH-klo-veer), foscarnet (pronounced fos-KAHR-net), ribovarin, and azidothymidine (AZT, pronounced AZE-ih-do-thigh-mih-deen). These drugs are more effective with some forms of encephalitis than with others.

Other drugs are available for the treatment of the symptoms of encephalitis. For example, corticosteroids (pronounced kor-tih-ko-STAIR-oids) are used to reduce inflammation and swelling. Anticonvulsant drugs can be used to control seizures. Fever can be treated with aspirin or acetaminophen. Aspirin should not be given to childen due to the risk of Reye's syndrome (see Reye's syndrome entry).

PROGNOSIS

Encephalitis symptoms may last several weeks. Most cases of encephalitis are mild, however, and patients recover quickly and completely. They experience no further problems after the disease has disappeared.

About 10 percent of all encephalitis patients die from the infection. The death rate varies, depending on the kind of encephalitis. For example, there aren't any effective treatments for eastern equine encephalitis and the death rate is usually about 30 percent. Herpes encephalitis has one of the highest death rates. With treatment, 15 to 20 percent of herpes encephalitis cases result in death. Without treatment, the number of deaths jumps to 70 to 80 percent.

Some people do experience long-term neurological damage (damage to the nervous system, including the brain) after having encephalitis. The effects include personality changes, memory loss, language difficulties, seizures, and partial paralysis.

PREVENTION

There are two major ways to avoid encephalitis. One is to reduce the risk of getting the disease from another human who has been infected. Most infections of this kind are spread hand-to-hand or mouth-to-hand. To avoid transmission of this kind, a person should remember to wash his or her hands frequently during the day.

A second way to avoid encephalitis is to reduce the chance of being bitten by mosquitoes, rats, bats, and other animals that carry the disease. One should be aware when such animals may be around. For example, mosquitoes tend to be more common in warm, moist areas. They tend to be more active at dawn and dusk. A person who has to be outdoors during these times should try not to have bare arms and legs. Mosquito repellent should be used to prevent bites.

Vaccines (treatments that enable the body to build immunity to certain viruses) are available for some viruses, such as polio, herpes B, and equine encephalitis. A person who may be at risk for these viruses should have injections of the vaccines.

FOR MORE INFORMATION

Organizations

Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (404) 639–3311. http://www.cdc.gov.

Encephalitis

What Is Encephalitis?

How Common Is Encephalitis?

Is the Disease Contagious?

How Is Encephalitis Spread?

What Are the Signs and Symptoms?

How Do Doctors Make the Diagnosis?

How Do Doctors Treat Encephalitis?

How Long Does the Illness Last?

What Are the Complications?

How Is Encephalitis Prevented?

Resources

Encephalitis (en-seh-fuh-LYE-tis) is inflammation of the brain.

KEYWORDS

for searching the Internet and other reference sources

Arboviruses

Herpes simplex virus

Immunizations

La Crosse encephalitis

Meningitis

Mosquito-borne illnesses

St. Louis encephalitis

Tick-borne illnesses

West Nile virus

What Is Encephalitis?

There are several different causes of encephalitis. The most common is infection, usually by a virus. The condition can range from mild to severe, depending on the type of germ producing the infection. Encephalitis can occur with certain childhood viral illnesses, such as mumps, measles, varicella (chicken pox), rubella (German measles), or mononucleosis.

A much more serious type of encephalitis is caused by the herpes simplex virus* (HSV). HSV rarely infects the brain, but when it does, it can be life threatening. West Nile virus, which first arrived in the United States from other parts of the world in the late 1990s, can cause encephalitis as well. Infected birds carry this virus, but mosquitoes can pick up the virus when they bite infected birds and then spread the virus to humans through a bite.

*herpes simplex

(HER-peez SIM-plex) virus is a virus that can cause infections of the skin, mouth, genitals, and other parts of the body.

Encephalitis may develop in a person who has meningitis (meh-nin-JY-tis), an inflammation of the membranes surrounding the brain and spinal cord, called the meninges (meh-NIN-jeez). It also can be a complication of other infectious diseases, such as rabies, cytomegalovirus* infection, listeriosis*, syphilis*, or Lyme disease. In people with a weakened immune system, for instance, those with HIV/AIDS, infection by parasites can lead to encephalitis, especially the parasite that causes toxoplasmosis*.

*cytomegalovirus

(sy-tuh-MEH-guh-lo-vy-rus), or CMV, infection is very common and usually causes no symptoms. It poses little risk for healthy people, but it can lead to serious illness in people with weak immune systems.

*listeriosis

(lis-teer-e-O-sis) is a bacterial infection that can cause a form of meningitis in infants and other symptoms in children and adults.

*syphilis

(SIH-fih-lis) is a sexually transmitted disease that, if untreated, can lead to serious lifelong problems throughout the body, including blindness and paralysis.

*toxoplasmosis

(tox-o-plaz-MO-sis) is a parasitic infection that usually causes no symptoms in healthy people, but it can cause serious problems in unborn babies and people with weak immune systems.

How Common Is Encephalitis?

Each year, several thousand cases of encephalitis are reported to the U.S. Centers for Disease Control and Prevention. Health officials believe that many more cases go unreported when the symptoms are mild.

Is the Disease Contagious?

Although the brain inflammation itself is not contagious, viruses that cause encephalitis may be contagious. When someone contracts the same virus that a person with encephalitis has, however, it does not mean that he or she also will develop encephalitis.

How Is Encephalitis Spread?

Because several different germs can cause encephalitis, spread of the infection may take place in different ways. For example, mosquitoes transmit viruses that cause West Nile encephalitis, St. Louis encephalitis, and western equine encephalitis. Other viruses (such as herpes simplex virus or varicella-zoster, var-uh-SEH-luh ZOS-ter, virus, which causes chicken pox) are spread in fluids from the mouth, throat, or nose; tiny drops of these fluids, such as saliva and nasal mucus*, may be sprayed into the air

*mucus

(MYOO-kus) is a thick, slippery substance that lines the insides of many body parts.

by a cough or sneeze from someone who is infected. Ticks spread Lyme disease, and humans can contract rabies from the bite of infected animals, such as raccoons and bats.

What Are the Signs and Symptoms?

Many people who are infected with a virus that can cause encephalitis have only mild symptoms. Symptoms in people who develop encephalitis may appear suddenly and include headache, fever, sensitivity to light, loss of appetite, and a stiff neck and back. In more serious cases there may be high fever, nausea (NAW-zee-uh), vomiting, confusion, double vision*, personality changes, problems with hearing and speech, hallucinations*, sleepiness, clumsiness, muscle weakness, loss of sensation, and irritability. In the most severe cases, seizures* and loss of consciousness may occur. A person who has any of these symptoms requires immediate medical attention.

*double vision

is a vision problem in which a person sees two images of a single object.

*hallucinations

(ha-loo-sin-AY-shuns) occur when a person sees or hears things that are not really there. Hallucinations can result from nervous system abnormalities, mental disorders, or the use of certain drugs.

*seizures

(SEE-zhurs) are sudden bursts of disorganized electrical activity that interrupt the normal functioning of the brain, often leading to uncontrolled movements in the body and sometimes a temporary change in consciousness.

How Do Doctors Make the Diagnosis?

Doctors use several tests to diagnose encephalitis. Imaging tests, such as computerized tomography* scans or magnetic resonance imaging*, provide special views of the brain that allow doctors to check for swelling, bleeding, or other abnormalities. An electroencephalogram (e-lek-tro-en-SEF-a-loh-gram), which measures brain electrical activity, will show abnormal patterns in a person with encephalitis. Doctors also might order blood tests to look for the microorganism in the blood and tests that can tell whether the person’s body is producing antibodies* in response to a specific virus or bacterium. A spinal tap, also called a lumbar puncture, often is performed. In this procedure a needle is inserted into the lower end of the spine and a small sample of cerebrospinal (seh-ree-bro-SPY-nuhl) fluid, which surrounds the brain and spinal cord, is removed. This fluid is examined under a microscope and tested for signs of infection. In addition, cotton swabs can be used to take fluid samples from the nose, throat, and rectum* to test for certain viruses that might be causing the infection.

*computerized tomography

(kom-PYOO-ter-ized toe-MgAH-gruh-fee), or CT, also called computerized axial tomography (CAT), is a technique in which a machine takes many X rays of the body to create a three-dimensional picture.

*magnetic resonance imaging

(MRI) uses magnetic waves, instead of X rays, to scan the body and produce detailed pictures of the body’s structures.

*antibodies

(AN-tih-bah-deez) are protein molecules produced by the body’s immune system to help fight specific infections caused by microorganisms, such as bacteria and viruses.

*rectum

is the final portion of the large intestine, connecting the colon to the anus.

How Do Doctors Treat Encephalitis?

Encephalitis is a very serious disease that can be life threatening. Although very mild cases can be treated at home, it is often necessary for patients to be hospitalized. Patients usually are admitted to an intensive care unit, where doctors carefully monitor blood pressure, heart rate, and ability to breathe. Such patients may require a ventilator (VEN-tuh-layter), a machine that does the breathing for very ill people until they can breathe on their own again. Doctors also monitor the body fluids to help prevent or control swelling of the brain, which can lead to a dangerous increase in the pressure within the skull.

Several medications may be given to people with encephalitis. Over-the-counter medicines such as acetaminophen (uh-SEE-teh-MIH-noh-fen) may be used to treat minor symptoms such as fever and headache. Antiviral medications sometimes can help prevent the spread of the virus and are very important in the treatment of encephalitis caused by herpes simplex virus. If a patient is having seizures, anticonvulsants* may help control them. Anti-inflammatory medications called corticosteroids (kor-tih-ko-STIR-oyds) may lessen swelling in the brain.

*anticonvulsants

(an-tie-kon-VULsents) are medications that affect the electrical activity in the brain and are given to prevent or stop seizures.

How Long Does the Illness Last?

The acute phase of the disease, the time when symptoms are most severe, usually lasts up to a week. Full recovery can take much longer, often several weeks or months.

What Are the Complications?

Most people recover from encephalitis completely. For some people, however, swelling of the brain may lead to permanent brain damage. These patients may face long-term complications, such as learning disabilities, seizures, speech problems, memory loss, lack of muscle control, paralysis*, or coma*. In the rare cases where brain damage is severe, death can result. Infants younger than 1 year and adults older than 55 have the greatest risk of permanent brain damage and death from encephalitis.

*paralysis

(pah-RAH-luh-sis) is the loss or impairment of the ability to move some part of the body.

*coma

(KO-ma) is an unconscious state in which a person cannot be awakened and cannot move, see, speak, or hear.

How Is Encephalitis Prevented?

Some of the viral infections that can cause encephalitis, including measles, mumps, and chicken pox, can be prevented with vaccines given in childhood. To prevent encephalitis caused by West Nile virus or other viruses transmitted by mosquitoes, people are encouraged to avoid being outside at dawn and dusk, when mosquitoes are most active. If they do go out, they are advised to wear light-colored, long-sleeved shirts and long pants and to use insect repellent. Mosquitoes breed in places where there is standing water, such as in buckets, birdbaths, and flower pots, so draining these containers frequently can help control the mosquito population and decrease the risk of infection.

Causes OF Encephalitis

Encephalitis may be caused by a variety of viruses, bacteria, and other organisms. These agents include:

• Measles, chicken pox, rubella (German measles), mumps, polio, and other viral illnesses, which generally lead to a mild form of encephalitis known as postinfectious or para-infectious encephalitis.
• Enteroviruses (en-tuh-ro-VY-ruh-sez), viruses that typically infect the intestines and then may spread to other parts of the body, including the brain.
• Herpes simplex virus, a virus that can infect the mouth, skin, and other parts of the body.
• HIV (human immunodeficiency virus), the virus that causes AIDS (acquired immunodeficiency syndrome) and is transmitted when an infected person’s blood or body fluids are introduced into the bloodstream of a healthy person.
• Arboviruses (ar-buh-VY-ruh-sez), which multiply in and are transmitted by blood-sucking insects (such as ticks and mosquitoes) when they bite infected birds, rodents (chipmunks and squirrels, for example), and other small animals and then bite humans.
• Animal-borne illnesses, such as rabies, toxoplasmosis, cat scratch disease, and Lyme disease, that are transmitted to humans by contact with an infected animal’s saliva (through a bite or lick, for example), contact with an infected animal’s feces (FEE-seez, or bowel movements), or an insect that bites an infected animal and then bites a person.

See also

AIDS and HIV Infection

Cytomegalovirus (CMV) Infection

Herpes Simplex Virus Infections

Immune Deficiencies

Lyme Disease

Measles (Rubeola)

Meningitis

Mononucleosis, Infectious

Mumps

Rabies

Rubella (German Measles)

Syphilis

Varicella (Chicken Pox) and Herpes Zoster (Shingles)

West Nile Fever

Resources

Organization

U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333. The CDC provides fact sheets and other information on encephalitis at its website.

Telephone 800-311-3435 http://www.cdc.gov

Website

KidsHealth.org. KidsHealth is a website created by the medical experts of the Nemours Foundation and is devoted to issues of children’s health. It contains articles on a variety of health topics, including encephalitis.

http://www.KidsHealth.org

encephalitis (en-sef-ă-ly-tis) n. inflammation of the brain. It may be caused by a viral (e.g. herpes simplex) or bacterial infection or it may be part of an allergic response to a systemic viral illness or vaccination (see encephalomyelitis). e. lethargica a form of viral encephalitis that is marked by headache and drowsiness, progressing to coma (hence its popular name – sleepy sickness). It can cause postencephalitic parkinsonism. See also Rasmussen's encephalitis.

encephalitis Inflammation of the brain, usually associated with a viral infection; often there is an associated meningitis. Symptoms include fever, headache, lassitude, and intolerance of light; in severe cases there may be sensory and behavioural disturbances, paralysis, convulsions, and coma. Tests on cerebrospinal fluid provide a diagnosis of encephalitis.

en·ceph·a·li·tis / enˌsefəˈlītis/ • n. inflammation of the brain, caused by infection or an allergic reaction. DERIVATIVES: en·ceph·a·lit·ic / -ˈlitik/ adj.

encephalitis Inflammation of the brain, which may be due, for example, to virus infection.

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