Japanese B Encephalitis

Japanese encephalitis is a mosquito-borne disease caused by the Japanese encephalitis virus.  It occurs mainly in the rural and agricultural areas of Asia and Western Pacific.  In temperate regions such as China, Japan and Korea, the transmission is highest from April to September.  

Most infections are asymptomatic.  The incubation period is about 5-15 days.  Usual symptoms include headache, fever, nausea and vomiting.  Severe cases may progress to confusion and coma.  The mortality can be as high as 25%.   
Mode of Transmission
The virus is transmitted by the bite of infected Culex mosquitoes.  The mosquitoes bit domestic animals such as pigs and then carry the virus to others.   
Diseases Control
There is no specific treatment for this disease.  The mainstay of treatment is symptomatic and supportive.
Preventive Measures

Travelers can protect themselves by taking the following simple precautionary measures:

  • Avoiding outdoor exposure to mosquito bites at dusk and dawn, especially in rural area
  • Apply effective insect repellents with DEET to exposed parts of their bodies.
  • Vaccines are available which consist of 2 doses at an interval of 1-2 weeks. The course should be completed at least 10 days before departure.  An additional dose is recommended for those age over 60 at one month after the first dose. The vaccine is indicated mainly for persons spending 30 days or more in a rural agricultural endemic area during the transmission season.
Vaccination Schedule

For initial immunization, usually two injections are administered subcutaneously at an interval of 1-2 weeks.  One additional dose is recommended one month after the initial immunisation to those who are over 60 years of age.

For booster immunisation, one dose is recommended every year or at least every four years to maintain the immune level.  For children below 3 years of age, the dose should be decreased by halve for each administration.
Adverse Reactions
They mainly consist of local reactions showing varying degrees of induration, redness and tenderness, and systemic reactions as evidenced by chills, headache and fever.
Contraindications
The vaccine is not recommended for people suffering from severe febrile illnesses or other active infections.  Patients having heart, kidney or liver diseases, diabetes or other malnutrition states should not receive the vaccine.  Leukemic patients or patients having lymphomas or generalized malignancies should also avoid this vaccination.  Vaccination is also contraindicated in pregnant women, infants, and people with hypersensitivity reactions to previous vaccination.