Japanese encephalitis: problem in India
Japanese encephalitis is a mosquito-borne viral encephalitis.It is endemic in many regions of India.
The virus is particularly common in areas where rice cultivation occurs.
The irrigated rice fields attract the natural avian vertebrate hosts.They are breeding sites for mosquitoes such as Culex tritaeniorhyncus.
The mosquito which carries the Japanese Encephalitis virus
Culex tritaeniorhyncus
How does the disease spread?
Mosquitoes transmit the virus to humans. Humans get the disease.But humans don’t transmit the infection. Pigs and horses are amplifier hosts (that is the virus multiplies in their bodies ).
So vaccination of these additional amplifier hosts may definitely reduce virus transmission.
When does Japanese encephalitis occur?
In India, Japanese encephalitis outbreaks have been reported in most states and Union territories.
It occurs throughout the year.Significantly highest incidences occur during monsoon and post-monsoon period.
Who are most likely to get Japanese encephalitis?
In endemic areas unvaccinated children are most often affected.
But travelers of all ages may also be affected.
Statistics which give you a better perspective
Most human cases of JE (Japanese encephalitis) may be asymptomatic. Overt encephalitis may occur in 1 of 20-1000 cases.
However, the encephalitis when it occurs is severe.
Fatality being as high as 25%.
Significantly children constitute an unfortunately high percentage of the fatalities.
World Health Organization (WHO) estimates that there occurs at least 50,000, reported fatal cases in Asia every year.
Of this at least, 10,000 are children.
Serious neuropsychiatric sequelae may be observed in the encephalitis survivors in up to 30% cases.
Out of many causes of encephalitis, JE is the most significant one which is vaccine preventable.
How can JE be Prevented?
- Public health campaigns to raise awareness
- Surveillance for cases of encephalitis
- Vector(mosquito) control
- Vaccination.
Who needs Japanese encephalitis vaccine
- Children and adults in endemic , epidemic zones
- Travellers to endemic zones
- A spending month or longer in endemic area during the transmission season.
- Amplifier host vaccination( Pigs, horses)
Vaccination in India
1)Live stable, neuro attenuated strain of cell culture derived SA-14-14-2 vaccine.
Recent Indian data on efficacy /effectiveness suggests the need for two doses of vaccines for primary vaccination schedule.
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Primary immunization
Children less than 3 years:
2 doses of 0.25 ml.1st dose at 9 months along with measles vaccine.
2nd dose at 16 or 18 months at the time of first DTP booster.
Children more than 3 years, adolescents, adults less than 50 years:2 doses of 0.5 ml on days 0 and 28.
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Booster Doses
Long-term protective efficacy and requirement for boosters are still not fully determined
Adults have been recommended for a booster after 12 months.
2)Purified Japanese encephalitis Inactivated Vaccine(Human)
- It contains the JEV strain 821564-XY in a purified and inactivated form.
- Indicated above one year of age.
Composition
- JEV strain 821564-XY in a purified and inactivated form.
- Aluminium hydroxide gel
- Thiomersal(preservative)
- Phosphate Buffered solution
Site and route: Intramuscularly into deltoid of upper arm of adults
Children :anterolateral thigh
Primary vaccination dosage and schedule:
2 dose 0.5 ml each
First dose: Day 0
Second dose:28 days after the first dose
One dose offers >98% protection
You might need a booster:
- when visiting an endemic area , with chance of re-exposure
- more than one year has passed, since primary vaccination was given.
Possible Adverse effects of JE vaccine:
- Fever
- headache
- myalgia
- hypersensitivity reaction.
Contraindications of Japanese Encephalitis vaccine:
- Patient with known or suspected hypersensitivity to vaccine components.
- Severe allergic reaction after previous dose of vaccine.
- A patient who has fever.
The Big picture on Japanese encephalitis vaccine
The risk of JE associated encephalitis, it’s resultant mortalities and serious morbidity is on one side.This is weighed against the relatively safe vaccine with few side effects.The balance of facts makes this vaccine a very important vehicle to fight the endemic nature of the disease in India.
There’s a need for public awareness and vector control measures.These are the backbone of effective prevention.Prevention, as usual, is the best policy.Stay informed, take charge and make an informed decision.
Is your home mosquito Free?
Let me know in the comments section below.
Reference:
- VermaR.Hum Vaccin Immunother. 2012 Apr;8(4):491-3. doi: 10.4161/hv.18925. Epub 2012 Feb 28. Japanese encephalitis vaccine: need of the hour in endemic states
- Best of Indian Pediatrics vol1. Devendra Mishra, Dheeraj Shah
- Harrison’s Principles of Internal Medicine