Japanese encephalitis

Japanese encephalitis   

Japanese encephalitis as its name suggests is a form of encephalitis that is inflammation of the encephalon that is cerebrum, the part of the brain. It is infectious disease spreading year to year in endemic areas. Every year it spreads after start of rainy season in the endemic parts of the world. It badly affects children less than 15 years of age, Its mortality rate is as high as 30 percent with those who recover may have permanent disability and neuropsychiatric disorders.

Japanese encephalitis occurs in nearly all Asian countries and mainly affects of countries that are in tropical and subtropical region and temperate region where temperature is hot and humid. Currently nearly 23 countries of Asia which are very densely populated are endemic to the Japanese encephalitis disease.

Epidemiology of Japanese encephalitis disease

Japanese encephalitis disease is endemic to the densely populated nations of the Asia specially south east Asia. It has propensity to spread to other areas too. Considering mortality rate reaching to 30 percent and significant proportion suffering from neuropsychiatric illness after the recovery from the disease it has been a serious public health concern in the many countries.

WHO estimates that nearly 50 thousand cases occur annually and 15 thousand of them die. The actual burden of disease may be 10 times higher than that reflected in the WHO reports. It is estimated that in last 60 years nearly 10 million children were affected by the Japanese encephalitis disease and 3 million of then died and nearly 4 million had permanent neurological disability. There is diagnostic challenge as it is difficult to do the clinical diagnosis and poor lab support in the affected areas. All the cases are not getting reported to get the real idea about the magnitude of the disease.

In India Japanese encephalitis is reported in 231 districts of 23 states. 37 more districts were added to this number reaching total to 268. So, Japanese encephalitis is spreading in other regions of the country. Inapparent infection tends to outnumber the clinical infection by 250 to 1000 times. The inapparent infection and disease provides the lifelong immunity. Highest risk is seen in children of 1-15 years age in rural areas and occurs in monsoon and post monsoon time.


In north temperate areas, which include countries like Japan, Taiwan, Nepal and North India, it tends to occur from May to October.

In southern tropical areas, which include South India, Indonesia and Sri lanka, It tends to occur from Jul to Dec.

Affected age 

Previously it was thought to be a disease of childhood. Now it is found that Japanese encephalitis can affect all age groups. In children less than 15 years old it is 10 times more common than in those more than 15 years old. In some populations almost half of the total cases are found in those more than 15 years of age and older.

About Japanese encephalitis virus: 

Japanese encephalitis is caused by Japanese encephalitis virus. This is single stranded RNA virus. It belongs to Family Flaviviridae.

How Japanese encephalitis virus is spread?

Japanese encephalitis virus is spread by mosquito bites. Mosquito of culex type spread this virus. Culex tritaeniorhynchus summarosus, this night biting mosquito mainly feeds on large domestic animals and birds and only infrequently bites human. This is the only vector to spread the Japanese encephalitis virus. 

Pigs serve as amplifying host for the Japanese encephalitis virus. Temperate, tropical or subtropical climate and pigs and humans at same location are the factors that favour the spread of the Japanese encephalitis virus.

Clinical manifestations of Japanese encephalitis:

  •  Clinical manifestations develop in four stages of the disease.
  • Incubation period lasts for 4 to 14 days.
  • Four stages of illness are prodromal illness, acute stage, subacute stage and convalescent stage.
  • Prodromal stage lasts for 2-3 days then followed by acute stage 3-4 days then subacute stage lasting for 7-10 days and convalescent stage lasting for 4-7 weeks.
  • The onset is abrupt and is featured by fever, headache, anorexia, nausea, abdominal pain and vomiting, respiratory symptoms and sensory changes including psychosis.
  • Generalized tonic clonic seizures are seen in some patients with parkinsons like feature and cogwheel rigidity in few cases.
  • Central nervous system signs may change rapidly as hyper reflexia to hyporeflexia. 
  • Sensorium is altered and patients may show confusion, delirium, decreased consciousness and leads to coma.
  • Albuminuria is common and those who deteriorate usually falls to coma and death in 10 days.

How the Japanese encephalitis is diagnosed?

  • After thorough history and clinical exam findings and considering the endemicity and local transmission season, the disease is suspected.
  • Those who are suspected having Japanese encephalitis undergo antibody tests antibody against Japanese encephalitis.
  • Detection of anti Japanese encephalitis IgM antibody in serum confirms the diagnosis.
  • Four fold rise of IgG against Japanese encephalitis when compared to convalescent serum is also diagnostic.
  • The virus can be detected by polymerase chain reaction.

What is treatment of Japanese encephalitis?

There is no specific treatment of Japanese encephalitis present currently. The symptomatic treatment is given to support the life and to support the nutrition.

The treatment is aimed at controlling the seizures and complications of encephalitis.

To control seizures medicines like phenytoin and leveteracetam are used.

If there is breathing difficulty supplemental oxygenation may be needed.

Ventilatory support needed in life threatening respiratory failure.

In encephalitis stage when child suffers depressed consciousness and coma there is need to maintain the nutrition as good as possible. Patient may need TPN if this stage is prolonged.

Even with best support mortality is high. Post disease complication like neuropsychiatric illness may remain. Patients need psychiatric support for the same.

What is prognosis of the Japanese encephalitis?

The mortality due to disease remains high ranging from 24 -42 percent. Mortality is highest in age group 5-8 years and above 65 years of age. 

The neuropsychiatric sequelae may be seen in 70 percent patients after recovery.

Important common sequelae are

  • Mental deterioration.
  • Emotional instability.
  • Personality changes.
  • Motor abnormality.
  • Speech disturbances.

How to prevent Japanses encephalitis?

This is preventable disease. Multifold strategy is needed to control the spread of infection. Mosquito control measures are utmost important. Using mosquito nets in nights with mosquito repellents and mosquito repellent fogging is recommended. The breeding places of the mosquito are controlled. 

Pigs should be raised away from residential areas.

Japanese encephalitis vaccines are available and suggested to be included in the national immunization schedules. 

Both live attenuated and killed vaccines are present currently and used.

About Japanese encephalitis (JE) vaccine:

  • Recommended only for individuals living in endemic districts. Both rural and urban children in a district should be vaccinated.
  • Three types of new generation JE vaccines are licensed in India: One, live attenuated, cell culture-derived SA 14-14-2, two inactivated JE vaccines, namely “vero cell culture-derived SA 14-14-2 JE vaccine” (JEEV® by BE India) and three “vero cell culture-derived, 821564XY, JE vaccine” (JENVAC® by Bharat Biotech).
  • Jeev, Jenvac, Ixiaro and Imojev are some brands of Japanese encephalitis vaccine.

Live attenuated, cell culture-derived SA-14-14-2:

  1. Minimum age: 8 months.

2. Two-dose schedule, first dose at 9 months along with measles and rubella (MR) vaccine and second at 16‒18 months along with diphtheria, tetanus toxoids and pertussis (DTP) booster.

3. Not available in private market for office use.

Inactivated cell culture-derived SA 14-14-2 (JEEV® by BE India):

1. Minimum age: 1 year [US Food and Drug Administration (FDA): 2 months].

2. Primary immunization schedule: Two doses of 0.25 mL each administered intramuscularly on days 0 and 28 for children aged ≥ 1 to ≤ 3 years.

3. Two doses of 0.5 mL for children >3 years and adults aged ≥18 years.

4. Need of boosters still undetermined.

Inactivated Vero cell culture-derived Kolar strain, 821564XY, JE vaccine (JENVAC® by Bharat Biotech):

1. Minimum age: 1 year.

2. Primary immunization schedule: Two doses of 0.5 mL each administered intramuscularly at 4 weeks interval.

3. Need of boosters still undetermined.


Catch-up vaccination:

1. All susceptible children up to 15 years should be administered during disease outbreak or ahead of anticipated outbreak in campaigns

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