Japanese Encephalitis Virus

It is common in the South East Asia and Far East.

Epidemic and sporadic cases can occur.

Transmission between birds and animals occur by the bites of Culex mosquitoes (feeds in the night).

Person to person transmission is rare.

Pigs can be considered as amplifying host.

JE mainly affects children under the age 15 years.

Fatality rate is between 10-60 %.

In endemic areas the seroprevalance is very high

Incubation period is between 1 and 6 days.

 

Clinical Presentations

Asymptomatic infection is common.

Abrupt onset with flu like symptoms is common- coryza, headache and cough.

There is also an increase in intracranial pressure.

Aseptic meningitis is common in children and it may present with febrile convulsion.

Other patients may present with Polio like acute flaccid paralysis.

 

Uncommon presentations include

Upper motor neuron signs- rigidity, spasm, flexor an extensor posturing

Parkinson sign – tremor, cogwheel rigidity

 

Complications

Neuropsychiatric problems- aphasia, slurred speech & intellectual impairment.

Gastric haemorrhage

Pulmonary oedema

Secondary bacterial infection (Pneumonia and UTI)

Investigations

CBC- Leukocytosis, increase in PMNL.

CSF- increase in protein level and cell count. Normal glucose. Protein <900mg/l.

EEG- non-specific abnormal EEG reading.

CT Scan- non-enhancing low density area in the thalamus, basal ganglia and mid-brain can be found.

MRI is more sensitive.

 

Tests

Viral isolation- suckling mouse, vero cell and LLC MK cell

EIA- IgM and IgG in serum and CSF

 

Management

 

There is no specific treatment

Supportive and symptomatic.

The main objective of therapy in hospitalised  patient is reducing the case fatality rate by reducing intracranial pressure and convulsions. These include

  • Positioning of patients

  • Controlling the body temperature

  • Sedating the patient with diazepam

  • Controlling seizure with anticonvulsant drugs.

  • Keeping fluid and electrolyte balance

  • Reducing IC pressure with mannitol or fursamide.

Prevention

Formalin inactivated vaccine has been used widely and found to be effective. Recently attenuated vaccine has been developed and used in China.

Insect repellent and bed net may be effective measures.

Wearing long sleeves shirt and long trousers.

Animal should be kept away from residential area.

Effective vector control.

Use of insecticide. 

 

 

 

Text Box:   Japanese encephalitis virus vaccination Formalin inactivated vaccine cultivated on mice brain. Two doses are given at interval of 1-2 weeks, subcutaneously. Most individuals respond to the vaccine (91 %). The live vaccine is cheaper and more effective.   Indications ü      For people living in endemic countries. ü      For travellers to endemic countries for more than 3 weeks. ü      To control epidemic. ü      For laboratory staff working on live JE virus.   Contraindications       Fever and acute infection       Allergic reactions to JEV vaccine   Adverse effect Local- tenderness, redness and swelling Fever, headache and rash may be seen in 10 % of recipients. Serious complication is rare. Hypersensitivity reaction and neurological problems.