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Encephalitis, Herpes Simplex

The information in NORD’s Rare Disease Database is for educational purposes only. It should never be used for diagnostic or treatment purposes. If you have questions regarding a medical condition, always seek the advice of your physician or other qualified health professional. NORD’s reports provide a brief overview of rare diseases. For more specific information, we encourage you to contact your personal physician or the agencies listed as “Resources” on this report.

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Synonyms of Encephalitis, Herpes Simplex

Disorder Subdivisions

General Discussion

Herpes simplex encephalitis (HSE) is a rare neurological disorder characterized by inflammation of the brain (encephalitis). Common symptoms include headaches, fevers, drowsiness, hyperactivity, and/or general weakness. The disorder may have some symptoms similar to those associated with meningitis, such as a stiff neck, altered reflexes, confusion, and/or speech abnormalities. Skin lesions usually are not found in association with herpes simplex encephalitis. Herpes simplex encephalitis is caused by a virus known as herpes simplex virus (HSV).


Symptoms associated with herpes simplex encephalitis usually develop over several days, often without warning. Early symptoms include headaches, fevers, and seizures. Additional symptoms include drowsiness with general weakness (stupor), and confusion or disorientation.

After the initial symptoms appear, affected individuals may develop speech abnormalities such as a diminished ability to communicate by speech, writing, and/or signs (aphasia), absence of the sense of smell (anosmia), and memory loss. In some cases, behavioral changes such as hyperactivity or psychotic episodes occur. Some symptoms of herpes simplex encephalitis may mimic meningitis. These symptoms may include a stiff neck, altered reflexes, confusion, convulsions, and paralysis.

Individuals with herpes simplex encephalitis may develop more severe symptoms, including loss of consciousness, hallucinations, and partial paralysis (hemiparesis). In some rare cases, herpes simplex encephalitis may affect the nerve-rich membrane lining the eyes (retina), resulting in inflammation of the retina (retinitis).


Herpes simplex encephalitis is a complication of infection with the herpes simplex virus. In most cases, the disorder results from herpes simplex virus type I (HSV-I). In rare cases, usually in newborns (neonatals), the disorder is caused by herpes simplex virus type II (HSV-II).

Herpes simplex infection is an acute viral disease usually spread from person to person. It is marked by small fluid-filled blisters appearing on the lips or genitals often accompanied by fever. Herpes simplex encephalitis rarely occurs in conjunction with oral or genital lesions. The herpes virus may become immediately active or remain in the body in an inactive (dormant or latent) state. After being active, the virus may become inactive and then recur (reactivate).

Symptoms associated with herpes simplex encephalitis may occur due to tissue degeneration associated with bleeding (hemorrhagic necrosis) of a tongue-shaped lobe (i.e., temporal lobe) of the cerebral hemisphere.

Affected Populations

Herpes simplex encephalitis usually occurs during early childhood or adulthood. It affects males and females in equal numbers. The disorder is the most common form of acute encephalitis in the United States with approximately 2,000 cases occurring per year. It accounts for 10 percent of all cases of encephalitis in the United States per year.

Related Disorders

Symptoms of the following disorders can be similar to those of herpes simplex encephalitis. Comparisons may be useful for a differential diagnosis:

Encephalitis is an inflammation of the brain. There are several different types of encephalitis that differ in cause, parts of the body affected, severity, and areas of the world where they occur. The symptoms of these disorders may also overlap with or resemble other infectious disorders. Symptoms common to all forms of encephalitis include fever, fatigue, drowsiness, and confusion. Causes of encephalitis include herpes simplex virus, varicella zoster virus, arboviruses, and enteroviruses. Encephalitis may also occur secondary to other disorders.

Meningitis is a disorder characterized by inflammation of the membranes surrounding the brain and spinal cord. There are many types of meningitis, caused by many different infectious agents. The infection can range from mild to severe. Meningitis may also accompany other infections such as herpes simplex encephalitis. Symptoms may include fever, headaches, nausea, vomiting, and stiff neck. (For more information on this disorder, choose "meningitis" as your search term in the Rare Disease Database.)

Neurosyphilis occurs when the syphilis bacterium spreads to the central nervous system. Syphilis is a chronic infectious disease caused by a bacterium (microorganism) (treponema pallidum). Affected individuals may not develop any associated symptoms. In some cases, individuals will experience seizures, headaches, fevers, stiff neck, dementia, and behavioral abnormalities. (For more information, choose "syphilis" as your search term in the Rare Disease Database).

Standard Therapies

A diagnosis of idiopathic herpes simplex encephalitis is made based upon a detailed patient history, a thorough clinical evaluation, identification of classic symptoms, and a variety of specialized tests. These tests include polymerase chain reaction (PCR) in cerebrospinal fluid (CSF), which may confirm infection of CSF with the herpes simplex virus. In some cases, advanced imaging techniques such as computed tomography and magnetic resonance imaging (MRI) can also be beneficial in diagnosing a case of herpes simplex encephalitis.

Prompt treatment of individuals with herpes simplex encephalitis is important as it improves the efficiency of treatment options.

Treatment with the antiviral drug Zovirax (acyclovir) has resulted in a dramatic improvement of symptoms in most individuals with herpes simplex encephalitis. It is manufactured by GlaxoSmithKline.

Another antiviral drug that has been used to treat herpes simplex encephalitis is vidarabine. However, antiviral therapy may not benefit affected individuals in advanced stages of the infection. Antiviral therapy should be started as soon as herpes simplex encephalitis is suspected.

Seizures that are often associated with herpes simplex encephalitis may be treated with drugs that reduce, prevent, or suppress seizures (anticonvulsants).

Investigational Therapies

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

For information about clinical trials sponsored by private sources, contact:

Encephalitis, Herpes Simplex Resources



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Hokkanen L, et al. Cognitive recovery instead of decline after acute encephalitis: a prospective follow up study. J Neurol Neurosurg Psychiatry. 1997;63:222-27.

Paillard C, et al. Recurrence of herpes simplex encephalitis. Arch Pediatr. 1999;6:1081-85.

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Taylor WB, et al. Ocular infection with herpes simplex virus type 1: prevention of acute herpetic encephalitis by systemic administration of virus-specific antibody. J Infect Dis. 1979;140:534-40.

Report last updated: 2009/05/15 00:00:00 GMT+0