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Table of Contents > Conditions > Encephalitis, Viral
Encephalitis, Viral
Also Listed As:  Brain Inflammation, Viral Encephalitis
Signs and Symptoms
Risk Factors
Preventive Care
Treatment Approach
Nutrition and Dietary Supplements
Massage and Physical Therapy
Other Considerations
Prognosis and Complications
Supporting Research

Encephalitis is an inflammation of the brain caused, most often, by a viral infection. The specific viruses that cause encephalitis vary. Exposure to viruses that cause encephalitis occur mostly through insect bites. The virus enters through the blood stream and spreads to the brain, causing inflammation of the nerve cells (encephalitis) and/or surrounding membranes (meningitis). Encephalitis is different than meningitis, but these two brain infections often occur together. Although the vast majority of individuals with encephalitis recover after a long period of time, inflammation may cause irreparable damage to the brain, bleeding within the brain, and even death. An estimated 10,000 to 20,000 cases of encephalitis are reported annually in the United States.

Signs and Symptoms
  • 90% of people with encephalitis experience flu-like symptoms such as fever, sore throat, cough, and malaise
  • If meningitis accompanies encephalitis, an individual may experience headache, stiff neck, intolerance to light, and/or vomiting
  • A change in the level of consciousness, ranging from mild confusion to coma, develops in virtually all people with encephalitis; often includes disorientation and delusion with possible hallucinations, agitation, and personality changes
  • Seizures occur in up to 50% of individuals with encephalitis
  • Other signs and symptoms of encephalitis depend on which area of the brain is most affected; these may include an impaired ability to use or comprehend words or coordinate voluntary muscle movements, muscle weakness or partial paralysis on one side of the body, uncontrollable tremors or involuntary movements, and an inability to regulate body temperature


Arboviruses, or viruses carried by insects, are among the most common causes of viral encephalitis. Some of the major arboviruses include:

  • Eastern equine encephalitis - transmitted by mosquito; primarily affects individuals along the eastern seaboard of the United States; one-third of infected individuals die of the condition and many others suffer permanent brain damage
  • European and Far Eastern (Russian) encephalitis - transmitted by ticks; although vaccine against this type of encephalitis is available in Europe, there is speculation that it may cause serious side effects
  • Japanese encephalitis - transmitted by mosquito; widespread in Asia; between 10% and 30% of infected individuals, primarily children, die of the condition
  • La Crosse encephalitis - transmitted by mosquito; primarily affects children under 16 years of age in the upper Midwestern United States; approximately 1% of infected individuals die of the condition.
  • St. Louis encephalitis - transmitted by mosquito; primarily affects individuals in rural Midwestern and southern United States; 7% of infected children and 30% of infected elderly die of the condition
  • Venezuelan equine encephalitis - transmitted by mosquito; primarily affects individuals in Central and South America; fatalities rare in humans but common in horses; epidemics in people occasionally occur after an outbreak in horses
  • West Nile encephalitis - transmitted by mosquito; primarily affects individuals in Africa and the Middle East, but outbreaks have also been recently recorded in the United States (New York City area and parts of New England); infections are most common in children and the elderly; as many as 10% of infected individuals die of the condition
  • Western Equine encephalitis - transmitted by mosquito; primarily affects individuals in western United States and Canada; usually causes a mild infection in people, except in children under 1 year of age, who often suffer permanent complications; 3% of infected individuals die of the condition.

Other viruses that commonly cause viral encephalitis include:

  • Herpes simplex virus type 1 (HSV1)
  • Measles
  • Enteroviruses (viruses that typically occur in the gastrointestinal tract)
  • Mumps

Less common causes include:

  • Cytomegalovirus
  • Epstein-Barr virus (EBV)
  • Human immunodeficiency virus (HIV)
  • Varicella-zoster virus (VZV)
  • Rabies virus

Not all cases of encephalitis are caused by viruses. Some nonviral causes of encephalitis include:

  • Bacterial infection
  • Fungal infection
  • Parasitic infection
  • Noninfectious causes, such as allergic reactions or toxins

Risk Factors

The following factors may increase an individual's risk for becoming infected with viral encephalitis:

  • Very young or very old age
  • Exposure to mosquitoes or ticks
  • Compromised immune system
  • Not being immunized against measles, mumps, and rubella
  • Traveling to areas where viral encephalitis is prevalent
  • Handling potentially infected animals


Encephalitis is a serious condition, so diagnosis and initial treatment usually take place in a hospital setting. After performing a physical exam, a physician may take the following steps to diagnose the condition:

  • Blood test - detects viruses in the blood
  • Spinal tap - detects viruses in the cerebrospinal fluid
  • MRI and CT scan - determines whether bleeding is present in the brain
  • Electroencephalogram (EEG) - detects abnormal brain waves

Preventive Care

The most effective way for an individual to prevent encephalitis is to avoid contracting viruses that lead to encephalitis:

  • Take protective measures when working or playing outside, such as using insect repellant and wearing long pants and long sleeves
  • Immunize against viruses that lead to encephalitis with vaccines such as the measles, mumps, rubella (MMR), and rabies
  • Maintain a balanced diet to keep the immune system healthy
  • An infectious disease specialist may recommend a particular Japanese encephalitis vaccine for those traveling to Asia during the summer, but serious allergic reactions have been reported with its use

Treatment Approach

Because encephalitis is a serious condition that can cause severe complications, treatment usually occurs in the hospital and sometimes requires intensive care. Generally, there are no specific medications to treat the viruses causing encephalitis. HSV1, VZV, and EBV are exceptions to this rule, however, as acyclovir is an excellent treatment. Often, people with symptoms of encephalitis are treated with this medication until the virus causing the condition is identified. Behavioral techniques, such as those used to treat individuals with traumatic brain injury, have been recently explored in the treatment of individuals recovering from the condition. Although complementary and alternative therapies have not been extensively studied for the treatment of encephalitis, some studies indicate that scalp acupuncture, combined with proper medication, may aid in the healing process. Careful observation and supportive care, including rest, proper nutrition, and fluids are a mainstay of treatment for encephalitis and allow the body to fight the infection.


Medications used to treat viral encephalitis include:

  • Acyclovir - treats encephalitis caused by HSV, VZV, and EBV
  • Ganciclovir or foscarnet - treats encephalitis caused by cytomegalovirus and HSV1
  • Anticonvulsant medications - prevent and treat seizures associated with encephalitis

Nutrition and Dietary Supplements


Although nutrition and dietary supplements have not been scientifically evaluated for use in treating encephalitis in humans, some studies suggest that melatonin may protect animals from serious complications associated with the condition and even increase their survival rates. In one study of mice that had been infected with Venezuelan equine encephalitis virus, melatonin supplements significantly reduced the presence of viruses in the blood and decreased the rate of death by more than 80%. More studies are needed, however, to determine whether similar treatment may offer the same protection to humans with viral encephalitis.


Astragalus (Astragalus membranaceus)

Animal studies suggest that Astragalus (Astragalus membranaceus), an herb used in Asia to improve weakness and to enhance immune function, may also protect humans from contracting viral encephalitis. In one study, mice that were given astragalus extracts before being infected with Japanese encephalitis virus, had a 60% to 80% chance of survival. Mice that did not receive astragalus extracts before being infected with the virus only had a 10% chance of survival. More studies are needed, however, to determine whether similar treatment may offer the same protection to humans with viral encephalitis.

Professional herbalists may also use a combination of herbs to relieve the symptoms associated with viral encephalitis, such as cognitive impairment, visual and speech disturbances, and difficulty performing routine functions. This herbal mixture includes:

  • Ginkgo (Ginkgo biloba)
  • St. John's wort (Hypericum perforatum)
  • Rosemary (Rosmarinus officinalis)


A study of a small number of individuals with complications associated with encephalitis suggests that acupuncture delivered to the scalp may lessen the severity of such complications and reduce the symptoms associated with the condition. Some researchers theorize that scalp acupuncture is effective for individuals with encephalitis because all meridians converge at the head, and the method can stimulate and regulate qi throughout the entire body. More research is necessary, however, to conclusively determine whether scalp acupuncture is safe and effective for individuals with encephalitis.

Massage and Physical Therapy

Behavioral and Physical Training

Recently, behavioral and physical training techniques have been explored in the treatment of individuals recovering from encephalitis. In one case, a woman experiencing poor short-term memory and decreased muscle coordination as a result of viral encephalitis began to improve significantly after participating in a behavioral rehabilitation training program. As a result of the program, she gained a high level of independence and was able to return home from the hospital with only minimal assistance by a caregiver. More studies are needed to determine whether behavioral training is safe and effective for other individuals recovering from encephalitis.

Other Considerations

The most common cause of encephalitis in newborns is vaginal delivery from a mother who is infected with herpes simplex virus 2 (HSV 2). This infection in newborns is often severe and fatal. For this reason, cesarean section may be advised for pregnant women with a history of HSV 2, even if there is no sign of an active infection.

Prognosis and Complications

Full recovery from encephalitis can take weeks or months, during which time many individuals experience complications ranging from fatigue and difficulty concentrating to tremors and personality changes. The most severe complications associated with encephalitis result from the destruction of nerve cells in the brain that do not regenerate. The severity of complications depends on the condition of the immune system (whether it is healthy or weak) and the infection causing the encephalitis. For example, 80% of those infected with Eastern equine encephalitis, St. Louis encephalitis, and Japanese encephalitis, have permanent neurologic impairments (such as memory, speech, vision, hearing, muscle control, and sensation) and a very low survival rate, while those infected with EBV or Venezuelan equine encephalitis rarely experience any serious complications. The long-term outlook for those with HSV encephalitis depends primarily on how quickly the condition is treated.

Between 80% and 95% of individuals infected with viral encephalitis will survive the condition, but 20% will experience debilitating side effects or complications, such as memory loss or severe personality changes. The survival rate for those with HSV encephalitis increases dramatically from 30% to 70% when the condition is detected early and treated with antiviral medications.

Supporting Research

Abe T, Kojima K, Shoji H, et al. Japanese encephalitis. J Magn Reson Imaging. 1998;8(4):755-761.

Adams RD, Victor M, Ropper AH. Principles of Neurology. 6th ed. New York, NY: McGraw-Hill; 1997:749-755.

Arribas JR, Storch GA, Clifford DB, Tselis AC. Cytomegalovirus encephalitis. Ann Intern Med. 1996;125(7):577-587.

Bale JF Jr. Viral encephalitis. Med Clin North Am. 1993;77(1):25-42.

Ben-Nathan D, Maestroni GJ, Lustig S, Conti A. Protective effects of melatonin in mice infected with encephalitis viruses. Arch Virol 1995;140(2):223-230.

Bonilla E, Valero-Fuenmayor N, Pons H, Chacin-Bonilla L. Melatonin protects mice infected with Venezuelan equine encephalomyelitis virus. Cell Mol Life Sci 1997;53(5):430-434.

Clifton ER. Herpes simplex encephalitis: an overview. J Miss State Med Assoc. 1991;32(12):437-440.

Evansa RW: Diagnostic Testing in Neurology. Philadelphia, Pa: W.B. Saunders Company; 1999:187-188.

Fauci AS, Braunwald E, Isselbacher KJ, et al, eds. Harrison's Principles of Internal Medicine. 14th ed. Vol 1. New York, NY: McGraw-Hill; 1998:1136-1139, 2442-2445.

Feign RD, Cherry JD. Textbook of Pediatric Infectious Diseases. 3rd ed. Vol 1. Philadelphia, Pa: W.B. Saunders Company; 1992:445-452.

Gorbach SL, Bartlett JG, Blacklow NR: Infectious Diseases. 2nd ed. Philadelphia, Pa: W.B. Saunders Company; 1998:1408-1414.

Gresikova M, Kaluzova M. Biology of tick-borne encephalitis virus. Acta Virol. 1997;41(2):115-124.

Irani MT, Singh AR, Udwadia AD, Merchant RH. Neonatal herpes simplex virus-2 encephalitis. Indian Pediatr. 1995;32(4):476-480.

Johnson RT. Acute encephalitis. Clin Infect Dis. 1996;23(2):219-224.

Kajimura K, Takagi Y, Ueba N, et al. Protective effects of Astragali radix by intraperitoneal injection against Japanese encephalitis virus infection in mice. Biol Pharm Bull. 1996;19(6):855-859.

Katzmann S, Mix C. Improving functional independence in a patient with encephalitis through behavior modification shaping techniques. Am J Occup Ther. 1994;48(3):259-262.

Levitz RE. Herpes simplex encephalitis: a review. Heart Lung. 1998;27(3):209-212.

Liang D. Treatment of the sequelae of viral encephalitis by needling Sishencong (Extra). J Chinese Med. 1996;50:26.

Luft BJ, Remington JS. Toxoplasmic encephalitis in AIDS. Clin Infect Dis. 1992;15(2):211-222.

Mrak RE, Young L. Rabies encephalitis in humans: pathology, pathogenesis, and pathophysiology. J Neuropathol Exp Neurol. 1994;53(1):1-10.

O'Meara M, Ouvrier R. Viral encephalitis in children. Curr Opin Pediatr. 1996;8(1):11-15.

Roos KL.Encephalitis. Neurol Clin. 1999;17(4):813-833.

Rosen P, et al. Emergency Medicine: Concepts and Clinical Practice. 4th ed. Vol 3. St. Louis, Mo: Mosby; 1998:2198-2209.

Rubeiz H, Roos RP. Viral meningitis and encephalitis. Semin Neurol. 1992;12(3):165-177.

Rust RS, Thompson WH, Matthews CG, Beaty BJ, Chun RW. La Crosse and other forms of California encephalitis. J Child Neurol. 1999;14(1):1-14.

Samuels MA, Feske S. Office Practice of Neurology. New York, NY: Churchill Livingstone; 1996:401-408.

Skoldenberg B. Herpes simplex encephalitis. Scand J Infect Dis Suppl. 1996;100:8-13.

Toltzis P. Viral encephalitis. Adv Pediatr Infect Dis. 1991;6:111-136.

Whitley RJ, Kimberlin DW. Viral encephalitis. Pediatr Rev. 1999;20(6):192-198.

Zupanc ML, Handler EG, Levine RL, et al. Rasmussen encephalitis: epilepsia partialis continua secondary to chronic encephalitis. Pediatr Neurol. 1990;6(6):397-401.

Review Date: March 2001
Reviewed By: Participants in the review process include: Jacqueline A. Hart, MD, Department of Internal Medicine, Newton-Wellesley Hospital, Harvard University and Senior Medical Editor Integrative Medicine, Boston, MA; David Winston, Herbalist, Herbalist and Alchemist, Inc., Washington, NJ.

Copyright © 2004 A.D.A.M., Inc

The publisher does not accept any responsibility for the accuracy of the information or the consequences arising from the application, use, or misuse of any of the information contained herein, including any injury and/or damage to any person or property as a matter of product liability, negligence, or otherwise. No warranty, expressed or implied, is made in regard to the contents of this material. No claims or endorsements are made for any drugs or compounds currently marketed or in investigative use. This material is not intended as a guide to self-medication. The reader is advised to discuss the information provided here with a doctor, pharmacist, nurse, or other authorized healthcare practitioner and to check product information (including package inserts) regarding dosage, precautions, warnings, interactions, and contraindications before administering any drug, herb, or supplement discussed herein.

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