Japanese Encephalitis: Frequently Asked Questions (FAQs)

     What is Japanese encephalitis?

     How does it spread?

     Where and when does it occur?

     Am I at risk?

     What are the symptoms of JE infection?

     Can JE be confused with other diseases?

     How is it diagnosed?

     How is it treated?

     How can I prevent JE?

     Can I be vaccinated against JE?

1.   What is Japanese encephalitis?

Japanese encephalitis (JE) is a potentially fatal viral disease occurring primarily in Asia.  It is also the leading cause of viral neurological disease and disability in Asia. Patients who recover from the disease, may suffer life-long complications, such as paralysis and mental impairment. These occur particularly among infants and children.

2.   How does it spread?

The virus is transmitted through the bite of a type of mosquito called the Culex mosquito, which breeds in stagnant water.  Wild and domesticated animals like pigs and waterfowl serve as natural reservoirs for JE viruses. Culex mosquitoes get infected with the virus while feeding on the blood of infected animals. They then transmit the virus to humans that they bite.

JE does not spread directly from human to human.  It is also not spread through food consumption. Mosquitoes are the only mode of transmission of the JE virus.

3.   Where and when does it occur?

It is primarily a rural and seasonal disease: JE outbreaks usually occur during the rainy season in paddy-growing areas, when there is a large area of stagnant water. The mosquitoes breed in this water, resulting in a much higher likelihood of humans being frequently bitten. Occasionally, outbreaks have also been reported in peri-urban or slum areas where scavenging pigs are present and water-logged conditions exists during the rainy season.

4.   Am I at risk?

JE most commonly occurs among children between the ages of 1-15 years.  Children are at risk in areas wherever the disease is present, especially if they are involved in outdoor activities during and immediately after the rainy season. However, adults can be infected as well.

5.   What are the symptoms of JE infection?

Symptoms are usually seen 5-15 days after a mosquito bite and typically include high fever, headache, nausea and neck stiffness. Other symptoms may include change in behaviour, lethargy, sleepiness and irritability. On occasions, convulsions may also occur. 

However, in a large number of cases, the infection is mild and either there are no obvious symptoms, or there may only be mild fever with headaches. Studies have indicated that for every person who shows symptoms of the disease, there are 250 to 1000 infected persons with no obvious symptoms. In such cases, the infected person develops immunity to the disease.

6.   Can JE be confused with other diseases?

The clinical appearance of JE can be very similar to meningitis, cerebral malaria, typhoid fever, dengue fever and leptospirosis. For these reasons, laboratory confirmation of JE is essential.

7.   How is it diagnosed?

JE is diagnosed based on the clinical picture and confirmed by laboratory tests of blood and cerebrospinal fluid.

8.   How is it treated?

There is no specific treatment for Japanese encephalitis because existing antivirals are not effective against this virus.   However, supportive treatment and good nursing care can significantly improve the outcome, mitigate neurological complications and avert possible death.

9.   How can I prevent JE?

         Wear protective clothing i.e. clothing that cover the body.

         Use mosquito repellants, particularly when engaged in outdoor activities during the rainy season.

         Avoid staying outdoors in the early mornings or late evenings during the rainy season.

         Vaccinate children against JE.

10.     Can I be vaccinated against JE?

Effective vaccines against JE are available, and vaccination has proven to be effective in controlling the spread of JE.  Children should be vaccinated in areas where JE infection can occur.

There are currently two types of JE vaccines:

1.      A cell-culture derived, live attenuated JE vaccine:  A safe and effective vaccine, that is currently being used in many JE-endemic countries including Sri Lanka, Nepal and India. A single dose followed by a booster dose after a year provides very good protection.

2.      A mouse brain-derived inactivated JE vaccine that is also considered safe and effective, but may result in tenderness, redness or swelling at the site of injection in some people.  The vaccination schedule is usually two initial doses four weeks apart, followed by a booster after a year. It is currently being used in Thailand.