Japanese Encephalitis

Japanese encephalitis is a mosquito-borne flavivirus infection of the central nervous system. It is the leading cause of viral encephalitis in Asia.

Transmission

• Japanese encephalitis virus is harboured by pigs/birds and transmitted to humans through the bite of an infected Culex mosquito.
• No human to human transmission occurs.
• Culex mosquitoes breed in water pools and rice paddies, preferentially feeding on animals/birds.
• Culex mosquitoes feed outdoors in the hours around dusk.

Vaccine Schedule

Rapid Schedule

Epidemiology + Risk Areas

• Japanese encephalitis is found mainly in South-East Asia and the Indian subcontinent, see map below.
• It is estimated that 60-70 000 cases occur annually in endemic regions with 13-20 000 deaths per annum.
• 40 clinical cases reported in travellers over 30 year period.
• Transmission patterns are highly specific to locations and vary year to year; in some countries transmission is seasonal and in others, disease occurs all year round.
• Risk is reduced at altitude and absent at high altitude.
• While traditionally considered a childhood disease, Japanese encephalitis can occur at all ages, especially in a population with no pre-existing immunity.

MAP OF RISK AREAS - Japanese Encephalitis

Clinical Aspects

• Incubation: 5-15 days.
• Illness: 10-14 days.
• Convalescence: 4-6 weeks.
• Infection is believed to confer lifelong immunity.

Risk of severe illness

• The majority of infections are asymptomatic.
• Approximately 1:250 of those infected have severe clinical disease.
• This ratio is higher in young children and mortality rate may be 30%.
• Symptomatic individuals have a high case fatality rate (25-30%) and there is a high rate of permanent neurological sequelae in survivors (30%).

Signs and Symptoms

• Fever.
• Headache.
• Convulsions.
• Encephalitis.
• Meningitis.
• Cranial nerve paralysis.

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