Structure & Property

Transmission

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment

Family: flavivirus

Genome: single-strand RNA, +ve polarity.

Size: 40-50nm

Icosahedral nucleocapsid.

Enveloped virion

One serotype

Antigenically related to dengue viruses

Transmitted to humans by certain species of Culex mosquito endemic to Asian rice fields.

Two main reservoir hosts: humans and pigs.

Infection follows bite by infected mosquito.

Virus replicates locally either in skin, lymphatics or endothelium of blood vessels.

Transient viraemia.

Virus enters nervous system:

- by capillary seeding through endothelium into meninges and brain.

- infection of nerve endings with subsequent axoplasmic transport to neurons.

Destruction of neurons & glial cells, perivascular inflitration with lymphocytes, focal hemorrhages.

Most common cause of epidemic encephalitis.

Abrupt onset with fever, headache, malaise, drowsiness, vomiting & generalized convulsions.

Marked and increasing disturbances of sensorium & signs of meningeal irritation.

CSF abnormalities: pleocytosis, elevated glucose and protein content.

Mortality:

- <10% in endemic areas

- 20-50% in severe epidemics.

Neurological sequelae:

- motor weakness

- mental backwardness

- behavior disorders

Diagnosis:

- haemagglutiation-inhibition for rise in antibody titer.

- IgM and IgG ELISA

IgM produced in CNS during encephalitis, appears in CSF

Japanese encephalitis vaccine:

- inactivated virus in mouse brain

- in three doses subcutaneously.

- recommended for travelers to endemic areas in Far East and Southeast Asia.

Pesticides to control mosquito vector.