Japanese Encephalitis
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Direct answer
Japanese encephalitis is a mosquito-borne flavivirus infection of the brain, spread by Culex mosquitoes that breed in flooded paddy fields and draw the virus from pigs and wading birds. Most infections are mild or asymptomatic, but severe disease causes encephalitis with a case fatality commonly quoted at 20 to 30 per cent. Bilateral thalamic lesions on MRI in a child with fever and altered sensorium strongly support the diagnosis.
What you must remember
- Virus and vector: a flavivirus transmitted mainly by Culex tritaeniorhynchus, which breeds in irrigated paddy fields.
- Reservoir: pigs act as amplifying hosts, and wading birds such as herons and egrets carry the virus; humans are dead-end hosts.
- Incubation: roughly 5 to 15 days after the mosquito bite.
- Clinical picture: sudden fever, headache, vomiting and altered sensorium, with seizures and neck stiffness in severe cases.
- Sequelae: parkinsonism, movement disorders, flaccid paralysis and cognitive deficits can persist in survivors.
- MRI: bilateral thalamic lesions, with basal ganglia and midbrain involvement, form a characteristic pattern.
- Diagnosis: JE-specific IgM antibody capture ELISA in CSF or serum, with CSF pleocytosis in most cases.
- Prevention: vaccination in endemic districts, given in infancy with a booster in the second year.
Where the exam tries to catch you
Most questions on this topic turn on the vector, the MRI pattern and the treatment answer.
- Trap: naming Aedes as the vector of JE Correct: Culex tritaeniorhynchus transmits JE, whereas Aedes is linked to dengue and chikungunya.
- Trap: choosing aciclovir as specific treatment for JE Correct: no proven antiviral exists for JE, so management is supportive, including seizure control and intensive care.
- Trap: expecting a temporal lobe pattern on MRI in JE Correct: the classic lesion is bilateral thalamic, with basal ganglia and midbrain involvement.
- Trap: considering humans as the source of spread Correct: humans are dead-end hosts, and transmission occurs through the mosquito and the animal reservoir.
Frequently asked questions
Which mosquito transmits the Japanese encephalitis virus?
Culex tritaeniorhynchus is the principal vector that transmits the Japanese encephalitis virus. The mosquito breeds in flooded paddy fields and feeds on pigs and wading birds. Aedes mosquitoes, which spread dengue, are not the vector for Japanese encephalitis.
What is the characteristic MRI finding in Japanese encephalitis?
The characteristic MRI finding in Japanese encephalitis is bilateral thalamic involvement, often with basal ganglia and midbrain lesions. These changes help separate Japanese encephalitis from other encephalitides. The MRI should be read alongside the history of mosquito exposure.
Is there a specific antiviral treatment for Japanese encephalitis?
No specific antiviral therapy has been proven effective for Japanese encephalitis. Management is supportive, including seizure control, airway protection and intensive care for severe cases. Aciclovir is used for herpes simplex encephalitis, not for Japanese encephalitis.
How is Japanese encephalitis diagnosed in children?
Japanese encephalitis is diagnosed by detecting JE-specific IgM antibodies in CSF or serum, usually by the IgM capture ELISA. The CSF often shows pleocytosis. A compatible clinical picture with recent mosquito exposure supports the diagnosis.
Which vaccine protects children against Japanese encephalitis in India?
Japanese encephalitis vaccine is given to children in endemic districts under the national immunisation programme. The schedule starts in infancy, with a booster in the second year of life. Vaccination is the main preventive measure against Japanese encephalitis.