Japanese encephalitis


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What is Japanese encephalitis?

Japanese encephalitis is a disease spread to humans by the bite of an infected mosquito. It is caused by a flavivirus similar to West Nile Virus. It cancause swelling of the brain, and possible long-term nerve and brain damage.

Japanese encephalitis can be prevented with a vaccine.

What is my risk? 

The risk to most travellers is low, particularly for those staying in urban areas.

Travellers to countries where Japanese encephalitis occurs are at greater risk if:

  • visiting rural and agriculture areas, particularly if the stay is over an extended period of time (one month or more). 
  • participating in outdoor activities such as camping, hiking, cycling or fieldwork.

How is it transmitted?   

  • Japanese encephalitis is spread through the bite of an infected Culex mosquito.
  • Mosquitoes that carry Japanese encephalitis bite mainly from sunset to sunrise.   

What are the symptoms?        

  • Symptoms can take between 5 to 15 days to appear. It is common for most people to show no symptoms.
  • In more severe cases, they:
    • usually include sudden onset of fever, headaches, and vomiting.
    • can also include neck stiffness, confusion, mental or behavioural changes, generalized weakness, paralysis, coma, seizures, or convulsions.
  • The disease is fatal in about 20-30% of severe cases who develop encephalitis.

Can Japanese encephalitis be treated?    

There is no specific treatment for Japanese encephalitis but medical care can help with recovery and the control of symptoms.

Where is Japanese encephalitis a concern?   

  • Japanese encephalitis occurs in almost all Asian countries and parts of the western Pacific.
  • It is mainly a threat in rural agricultural areas, particularly in areas where there is widespread irrigation, including rice-growing areas.
  • In temperate regions (regions with four seasons), such as China, Japan and Korea, transmission generally occurs in the summer and fall.  
  • In tropical and subtropical areas of Southeast Asia (for example, Indonesia, Malaysia, Singapore, Thailand, Vietnam), transmission can occur year-round.

A map of countries and risk areas for Japanese encephalitis is available on the World Health Organization’s website.

Recommendations

Consult a health care provider or visit a travel health clinic preferably six weeks before you travel.

  1. Protect yourself from mosquito bites
  2. Consider getting vaccinated
    • Most travellers going to countries where Japanese encephalitis occurs are at low risk; however, those who may be at high risk should consult a health care provider to discuss the benefits of getting vaccinated.
    • It is recommended that the following travellers consider getting vaccinated:
      • Those spending one month or more in a rural or urban area where Japanese encephalitis is present.
      • Those spending less than one month in a rural or urban area where Japanese encephalitis is present, but spending a large amount of time outdoors, particularly at night.
  3. Monitor your health
    • If you develop symptoms similar to Japanese encephalitis when you are travelling or after you return, see a health care provider and tell them where you have been travelling or living.
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