Japanese Encephalitis

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What is Japanese Encephalitis?

Japanese Encephalitis (JE) is the leading cause of viral encephalitis (inflammation of the brain) in Asia due to an arbovirus. It is a mosquito-borne infection that primarily affects children, and mostly in rural areas. The specific mosquito that transmits the disease is called Culex tritaeniorhynchus mosquito, which lives in marshes, flooded rice fields and standing water pools in planted fields.

How prevalent is JE?

Japanese Encephalitis victimizes between 30,000 to 50,000 people each year, with a death rate of about 10,000 annually. This translates to about 10 to 100 clinical cases per 100,000 population in endemic areas. Most (85%) of these children afflicted are younger than 15. The transmission period is usually in April or May and go on till about September or October, and higher during or shortly after the rainy season.

Which are the endemic areas?

There are three areas: (1) China and Korea; (2) Indian subcontinent including India, Bangladesh, Sri Langka and southern Nepal; and (3) Southeast Asian countries of Laos, Cambodia, Taiwan, Myanmar, Indonesia, Malaysia, Thailand, Philippines, and Vietnam. The greatest prevalence is in the Southern and Eastern Asia. Affected to a lesser degree are Singapore, Japan, Hong Kong and eastern Russia.

Is the disease spread from person to person?

No, Japanese Encephalitis is not contagious or spread from one to another individual. It is transmitted by carrier (infected) mosquito bites. Symptoms, if they occur, will present themselves between 4 to 14 days after the mosquito bites.

How severe are the symptoms?

Majority of the cases have mild or no symptoms at all. About one in 300 infections leads to symptomatic state. The symptoms are flu-like in nature, with rapid onset of fever, headache, chills, fatigue, nausea and vomiting. Gastrointestinal discomfort and dysfunction may be the overwhelming signs during the early stage. After 3 or 4 days symptoms indicating brain involvement may manifest with varying level o consciousness from confusion to coma. Seizures are also common. In 30% of cases, the condition results in encephalitis and become fatal. One third of the survivors (usually under age 10) will have grave neurological (brain damage and paralysis) and psychiatric complications.

Could adults be affected?

Yes. If the patient is a woman and is pregnant, intrauterine infection and abortion can happen during the first and second trimester of pregnancy. Those on their third trimester appear not to have any adverse affect on the baby.

Is the risk to travelers high?

No, the risk of infection among travelers is low, about 1 in a million, depending on the area, season and duration of travel. Visitors to endemic areas should take preventive measures from mosquito bites, such as wearing long sleeve shirts, use of insect repellents, mosquito nets (when necessary), etc.

How is diagnosis made?

Serological tests of blood and the spinal fluid of the patient is used to confirm the diagnosis. Recently, a new method has been developed: the dot-blot or immunoprecipitation IgM assays.

Is this infection curable?

There is no specific treatment for Japanese Encephalitis at this time, only for control of symptoms and management of complications. No antibiotic or viral drugs have been discovered so far to cure this illness. Prophylactic vaccination is the only means to control this viral infection,

What vaccines are available?

There are three types of vaccines for Japanese Encephalitis that are available: mouse brain-derived inactivated vaccine, cell culture-derived inactivated vaccine, and cell-culture-derived live attenuated vaccine.

How effective are the vaccines?

The 3-dose regimen of the mouse brain-derived inactivated vaccine is about 90% (9 out of 10) effective in preventing the disease. This vaccine, which is the only one that is commercially available in the world market, is used for adults and recommended for children older than one year of age.

What are the possible complications of vaccination?

Just like any drug or other vaccines, the vaccines for Japanese Encephalitis have possible complications, which may include redness, swelling and tenderness of the injection site; rash, fever, chills, headache, dizziness, nausea and vomiting, abdominal pains. Most of these symptoms disappear after a short while and can be alleviated with the use of acetominophen.

Is allergic reaction common?

Serious allergic reactions to the vaccine have been reported in one-tenth (0.1) of a percent. Some of the symptoms are shortness of breath and wheezes, hives and swelling of some parts of the body, including the breathing pipes. Severe allergic shock complication (anaphylaxis), though rare, can happen within minutes, or up to 9 days, after receiving the immunization.

Has the vaccine cause encephalitis itself?

Yes, there were reports of some cases of acute encephalitis in 1992 temporally associated with the JE vaccination campaign in Korea. Overall, and for practical purposes, the currently used vaccines have a proven safety record.

How should the vaccination be done?

Vaccination for JE is recommended as a standard part of the established schedules of vaccinations (for other diseases), as a part of the national immunization program of the region.

Any other vaccine on the horizon?

The Chinese vaccine (live attenuated virus) is presently on the spotlight for Japanese Encephalitis prophylaxis. The vaccine has been reported to be more effective than the mouse brain-derived vaccine, have fewer side effects, needs fewer doses and much cheaper. Although it has been used for more than 12 years already in China, there is still some concerns in the western world about its safety. The United States and other major countries have ongoing studies on this Chinese vaccine. The World Health Organization meanwhile has issued some guidelines to allow its use outside of China. Remember, prevention is the key in controlling this incurable, devastating and potentially fatal illness.

©2003Raoul R. Diez, M.A.O.D.