Information on the following diseases can be found in the Related Disorders section of this report:

• Murray Valley Encephalitis
• Saint Louis Encephalitis
• West Nile Encephalitis

Japanese Encephalitis is a rare viral disorder characterized by high fever, headaches, weakness, nausea, vomiting, mental deterioration, personality changes, psychoses, impaired speech, spastic rigidity, and paralysis of the face or extremities.

In adults, paralysis may occur on both sides of the body without altered sensation. The duration of symptoms can vary widely and convalescence may be prolonged. Some affected individuals may experience swelling and small areas of bleeding within the brain. Wasting away (atrophy) of brain and nerve cells may also occur. The immune system is also weakened by the virus, potentially making affected individuals vulnerable to more serious infections.
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Japanese Encephalitis is caused by the Japanese B Encephalitis Virus, an arbovirus (mediated via insect bites), and transmitted through the bite of infected mosquitoes. Symptoms occur as the virus directly invades the central nervous system causing selective infection, destruction of nerve cells, and weakening of the immune system.

Japanese Encephalitis occurs in approximately 20,000 people each year. The disorder erupts in the form of epidemics usually during the summer months in India, Bangladesh, the eastern part of Russia, China, Korea, Nepal, Burma, Viet Nam, and northern Thailand. In tropical areas of southeast Asia, southern India, southern Thailand, and Sri Lanka, the disease is present year-round and causes sporadic outbreaks. During the tropical rainy season, the illness can be transmitted in epidemic proportions.

Japanese Encephalitis is the leading cause of viral encephalitis in Asia, with approximately 30,000-50,000 cases being reported. Fewer than one case per year is reported among U.S. citizens and military personnel traveling to, or living in, Asia.
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Symptoms of the following disorders can be similar to those of Japanese Encephalitis. Comparisons may be useful for a differential diagnosis:

Murray Valley Encephalitis is also known as Australian X Disease and is characterized by severe brain inflammation. The virus which causes this disorder is related to the Japanese B virus and is transmitted from mosquitoes to birds to other mosquitoes. Cases among children tend to be most severe. The first noticeable symptoms may be headache, fever, a general feeling of discomfort, drowsiness and/or convulsions, and a stiff neck. Extensive brain damage may result.

Saint Louis Encephalitis is characterized by less severe inflammation of the brain and the sheath surrounding the brain and spinal cord. Group B Arbovirus causes this type of Encephalitis in sporadic outbreaks in urban areas of Missouri, Arizona, Colorado, Nevada, Texas, Indiana, Illinois, Kentucky, Florida, New Jersey, Pennsylvania, and the Ohio Valley. This disorder tends to be more prevalent during midsummer to early fall. High fever, headache, nausea, vomiting, tiredness, dizziness, neck stiffness, irritability, confusion, and speech problems may occur.

West Nile Encephalitis is also known as West Nile Fever and is characterized by severe headaches, high fever, enlargement of the lymph nodes, and inflammation of the sheath surrounding the brain and spinal cord. Inflammation of the spinal cord may also occur. Symptoms of this disorder may last only a few weeks, but it may cause permanent neurological damage.

In Asian nations, vaccinations are available that prevent Japanese Encephalitis. American travelers to areas at risk can obtain the vaccination in the United States. High risk areas include India, Bangladesh, the eastern part of Russia, China, Korea, Nepal, Burma, Viet Nam, northern Thailand, tropical areas of southeast Asia, southern India, southern Thailand, and Sri Lanka.

Short-term travelers to Asian urban centers are at low risk to contract this disorder. The mosquitoes which transmit the virus appear in the greatest numbers in rural areas where standing water may be common and are most active at dawn, dusk, and on overcast days. Precautions against mosquito bites such as sleeping in screened quarters under mosquito netting, wearing clothing that adequately covers the skin, and using insect repellents on exposed skin are also advised. Repellents containing over thirty percent active ingredient N,N-diethyl-meta-toluamide ("deet") are recommended.

Research on the antiviral inducing chemical known as carboxymethylacridanone (CMA), is underway to determine it's action against the Japanese Encephalitis virus. It has shown possible benefits against infection in laboratory animals. More investigation is needed before the treatment can be recommended for use in humans.

In 1999, a live attentuated vaccine for Japanese Encephalitis was designated as an orphan drug. Additional studies are required to determine the safety and efficacy of this treatment.

A pharmaceutical company known as Genelabs Technologies, Inc., is working on an RNA-binding drug program that has produced several compounds that potentially inhibit viral activity. It is hoped that this might lead to drug treatment options for RNA viruses, including yellow fever, hepatitis C, Japanese Encephalitis, and Dengue fever. More research is necessary to develop and test such drugs for safety and long-term effectiveness.

TEXTBOOKS
Thoene JG., ed. Physicians’ Guide to Rare Diseases. Montvale, NJ: Dowden Publishing Company Inc; 1995:545-46.

Fauci AS, et al., eds. Harrison's Principles of Internal Medicine, 14th Ed. New York, NY: McGraw-Hill, Inc; 1998:1138 .

Bennett JC, Plum F., eds. Cecil Textbook of Medicine. 20th ed. Philadelphia, PA: W.B. Saunders Co; 1996:1813-14.

Mandell GL, et al., eds. Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases. 4th ed. New York, NY: Churchill Livingstone Inc; 1995:1466-67.

REVIEW ARTICLES
Thompson, RF, et al., Travel vaccines. Infect Dis Clin North Am. 1999;13:149-67.

Sabchareon A, et al., Japanese encephalitis. Ann Trop Paediatr. 1998;18 Suppl:S67-71.

Abe T, et al., Japanes encephalitis. J Magn Reson Imaging. 1998;8:755-61.

JOURNAL ARTICLES
Nakashima A, et al., A case of Japanese encephalitis: CT and MRI findings in acute and
convalescent stages. Radiat Med. 1999;17:369-71.

Cuzzubbo AJ, et al., Evaluation of a new commercially available immunoglobulin M capture enzyme-linked immunosorbent. J Clin Microbiol. 1999;37:3738-41.

Defraites RF, et al., Japanese encephalitis vaccine (inactivated, BIKEN) in U.S. soldiers: immunogenicity and safety of vaccine administered in two dosing regimens. Am J Trop Med Hyg. 1999;61:288-93.

Khang G, et al., Preparation and characterization of Japanese encephalitis virus vaccine loaded poly(L-lactide-co-glycide) microspheres for oral immunization. Biomed Mater Eng. 1999;9:49-59.

Robert-Thomson L, Japanese encephalitis. Aust Fam Physician. 1999;28:480.