Viral encephalitis
medical conditions

Viral encephalitis

Explore the available health information, treatment context, and integrative evidence for Viral encephalitis.

Background
  • Encephalitis literally means brain infection. Strictly speaking, "-itis" means inflammation, which includes redness, swelling, pain, and warmth, and can be due to infection or other types of irritation. The brain can become infected with many different germs, including viruses, bacteria, fungi, and parasites. The symptoms of encephalitis include fever, chills, headache, altered mental status (confusion, delirium, and agitation), stiff neck, nausea, vomiting, seizures, coma (unconsciousness), and death. Viral brain infections are rarely as serious as other kinds of encephalitis.
  • Japanese encephalitis (JE), St. Louis encephalitis (SLE), and tick-borne encephalitis (TBE) are all caused by viruses in the flavivirus group. The viruses of these diseases are transmitted by mosquitoes or ticks. Each virus is particular to certain regions of the world. The following geographical distributions are typical for each disease: Japanese encephalitis is found in Asia and Australia; St. Louis encephalitis is found in North, Central, and South America. Tick-borne encephalitis is found in Europe and Asia.
  • JE can be a risk to travelers in rural areas of Japan, where there are 30,000 to 50,000 cases annually. Fewer than one case per year is reported in Americans traveling to or working in Asia. Birds and domestic pigs can carry the virus. Symptoms appear six to eight days after the mosquito bite. JE kills roughly 30% of its victims. Another 30% will have serious and permanent brain damage. A vaccine known as Japanese encephalitis virus vaccine is available, but it is expensive and occasionally causes significant side effects. Ten percent of patients report fever, headache, malaise, rash, and other reactions such as chills, dizziness, muscle pain, nausea, vomiting, and abdominal pain. Twenty percent report pain at the injection site. A few suffer generalized allergic reactions.
  • SLE is similar to West Nile virus, LaCrosse virus, and eastern and western equine encephalitis. Birds can carry the virus. Symptoms appear five to 15 days after the mosquito bite. It kills 5% to 30% of its victims. Between 1964 and 2005, 4651 cases were reported in the United States. It occurs most often in warmer weather, when mosquitoes abound.
  • TBE occurs in many parts of Europe and Asia. Several thousand cases are reported every year. The disease can also be acquired from raw cow, goat, and sheep milk, and from the air in infectious disease laboratories. Symptoms appear seven to 14 days after the tick bite. Permanent brain damage occurs in 10% to 20% of patients. Death occurs in only one percent to two percent of victims.
Risk Factors and Causes
  • Japanese encephalitis (JE) can be a risk to travelers in rural areas of Japan, where there are 30,000 to 50,000 cases annually. Fewer than one case per year is reported in Americans traveling to or working in Asia. Birds and domestic pigs can carry the virus.
  • St. Louis encephalitis (SLE) is similar to West Nile virus, LaCrosse virus, and eastern and western equine encephalitis. Birds can carry the virus. Between 1964 and 2005, 4651 cases were reported in the United States. It occurs most often in warmer weather, when mosquitoes abound.
  • Tick-borne encephalitis (TBE) occurs in many parts of Europe and Asia. Several thousand cases are reported every year. The disease can also be acquired from raw cow, goat, and sheep milk, and from the air in infectious disease laboratories.
  • Viral encephalitis is a brain infection caused by one of several viruses. Japanese encephalitis (JE), St. Louis encephalitis (SLE), and tick-borne encephalitis (TBE) are all caused by viruses in the flavivirus group. The viruses of these diseases are transmitted by mosquitoes or ticks.
Signs and Symptoms
  • The symptoms of viral encephalitis include fever, chills, headache, altered mental status (confusion, delirium, and agitation), stiff neck, nausea, vomiting, seizures, coma (unconsciousness), and death. Viral brain infections are rarely as serious as other kinds of encephalitis.
  • Symptoms of Japanese encephalitis (JE) appear six to eight days after the mosquito bite. JE kills roughly 30% of its victims. Another 30% will have serious and permanent brain damage.
  • Symptoms of St. Louis encephalitis (SLE) appear five to 15 days after the mosquito bite. It kills 5% to 30% of its victims.
  • Symptoms of tick-borne encephalitis (TBE) appear seven to 14 days after the tick bite. Permanent brain damage occurs in 10% to 20% of patients. Death occurs in only one percent to two percent of victims.
Diagnosis
  • The most definitive method of diagnosis of viral encephalitis is a brain biopsy, in which a small sample of brain tissue is removed and analyzed in a laboratory.
  • The typical methods for identifying viruses that may cause encephalitis are products of molecular biology research. Virus detection can be accomplished by fluorescent tagging using antigen-antibody reactions or by polymerase chain reaction (PCR). Their presence can also be detected by isolation of antiviral antibodies in the blood or spinal fluid of patients.
  • Fluorescent tagging is done by creating an antibody to the virus, attaching to it a chemical moiety that glows under ultraviolet light, mixing the tag with the sample to be tested, and looking for the fluorescent signature in the mixture.
  • PCR is a method of multiplying a segment of a gene millions of times so that it can be identified by fluorescence or other similar techniques. Antibodies in infected individuals take time to develop as the disease progresses, but they can also be identified by standard medical laboratory techniques.
Complications
  • Depending on the severity of the infection and the health status of the infected individual, viral encephalitis may cause seizures, coma, or death.
Treatment
  • Specific treatments for Japanese encephalitis, St. Louis encephalitis, or tick-borne encephalitis are currently unknown. Treatment generally focuses on the reduction of symptoms and prevention or management of complications. Therefore, treatment usually does not kill the virus but is directed towards sustaining the patient until the disease runs its course.
  • Treatment of viral encephalitis should focus on maintaining normal breathing, kidney and bladder function, fluid and electrolyte balance, and proper nutrition. In addition, patients should be monitored for additional infections, fevers, and bedsores.
  • Increased pressure in the brain should be monitored. Diuretics, mannitol, and hyperventilation may reduce this pressure. If seizures result from viral encephalitis, anti-seizure drugs such as phenytoin, valproic acid, and carbamazepine may be used.
  • For tick-borne encephalitis, specific immunoglobulin is available. An immunoglobulin is an antibody that is prepared in an animal and then purified and injected into a patient. Snake venom antitoxin is an example. These antibodies perform the same function as antibodies produced by the patient, but there is no wait time for the patient to produce them, which may take so long that the disease does its damage before they become effective.
Prevention
  • Except in rare circumstances, ordinary precautions against insect bites are advised to prevent these diseases. Insect repellants, clothing that covers most of the body, and socks and bed nets soaked in insecticide (permethrin) will prevent most arthropod-borne diseases.
  • A vaccine for Japanese encephalitis is available, but it is expensive and occasionally causes significant side effects. Ten percent of patients report fever, headache, malaise, rash, and other reactions such as chills, dizziness, muscle pain, nausea, vomiting, and abdominal pain. Twenty percent report pain at the injection site. A few suffer generalized allergic reactions. This vaccine is recommended only for those anticipating extended stays in high-risk regions.
  • A vaccine for tick-borne encephalitis is available in some countries but not in the United States. Its side effects include high fevers, particularly in children.
  • Individuals who travel to regions where these diseases are found must inform themselves of the risks and take whatever precautions are advised. In most cases, standard traveler vaccinations and routine precautions against known sources of disease are adequate.
References
  1. Centers for Disease Control. .
  2. Diagana M, Preux PM, Dumas M. Japanese encephalitis revisited. J Neurol Sci. 2007 Nov 15;262(1-2):165-70.
    View Abstract
  3. Dumpis U, Crook D, Oksi J. Tick-borne encephalitis. Clinical Infectious Diseases. 1999;2882-890.
    View Abstract
  4. Gould EA, Solomon T. Pathogenic flaviviruses. Lancet. 2008 Feb 9;371(9611):500-9.
    View Abstract
  5. Haglund M, Forsgren M, Lindh G, et al. A 10-year follow-up study of tick-borne encephalitis in the Stockholm area and a review of the literature - Need for a vaccination strategy. Scand J Infect Dis. 1996; 28(3)217-224.
    View Abstract
  6. Hoenninger VM, Rouha H, Orlinger KK, et al. Analysis of the effects of alterations in the tick-borne encephalitis virus 3'-noncoding region on translation and RNA replication using reporter replicons. Virology. 2008;377(2):419-30.
    View Abstract
  7. Japanese Encephalitis. U.S. Army Center for Health Promotion and Preventive Medicine, Entomological Sciences program, 5158 Blackhawk Road, Aberdeen Proving Ground, Maryland. .
  8. Kabilan L, Rajendran R, Arunachalam N, et al. Japanese encephalitis in India: an overview. Indian J Pediatr. 2004 Jul;71(7):609-15.
    View Abstract
  9. Kabilan L. Control of Japanese encephalitis in India: a reality. Indian J Pediatr. 2004 Aug;71(8):707-12.
    View Abstract
  10. Natural Standard: The Authority on Integrative Medicine. . Copyright © 2008.
  11. Pletnev AG, Bray M, Hanley KA, et al. Tick-borne Langat/mosquito-borne dengue flavivirus chimera, a candidate live attenuated vaccine for protection against disease caused by members of the tick-borne encephalitis virus complex: evaluation in rhesus monkeys and in mosquitoes. J Virol. 2001;75(17):8259-67.
    View Abstract
  12. Sejvar JJ, Bode AV, Curiel M, et al. Post-infectious encephalomyelitis associated with St. Louis encephalitis virus infection. Neurology 2004;63(9):1719-21.
    View Abstract
  13. Wootton SH, Kaplan SL, Perrotta DM, et al. St. Louis encephalitis in early infancy. Pediatr Infect Dis J 2004;23(10):951-4.
    View Abstract