Mode of Transmission of Japanese Encephalitis

• Japanese encephalitis is a vector borne disease.
• Several species of mosquitoes are capable of transmitting JE virus.
• JE is a zoonotic infection. Natural hosts of JE virus include water birds of Ardeidae family (mainly pond herons and cattle egrets). Pigs play an important role in the natural cycle and serve as an amplifier host since they allow manifold virus multiplication without suffering from disease and maintain prolonged viraemia.
• Due to prolonged viraemia, mosquitoes get opportunity to pick up infection from pigs easily.
• Man is a dead end in transmission cycle due to low and short–lived viraemia. Mosquitoes do not get infection from JE patient.

Japanese Encephalitis Vectors in India

• Japanese encephalitis virus isolation has been made from a variety of mosquito species.
• Culicine mosquitoes mainly Culex vishnui group (Culex tritaeniorhynchus, Culex vishnui and Culex pseudovishnui) are the chief vectors of JE in different parts of India.

The disease is transmitted to man by culex vishnui group. (C. Vishnui, C. pseudovishnui, C. tritaeneorhynchus). Man to man transmission has not been recorded so far.

Animal host
Pigs are a major source of reservoir of JE virus. Infected pigs do not show any overt symptoms of illness and can transmit the virus to human beings through mosquito bites. The pigs are considered as “Amplifiers” of the virus. Cattle, buffalow, horses are the animal hosts which can be infected.

Birds
Pond herons, cattle egrets, poultry ducks ardeid birds appear to be involved in the natural history of JE virus.

Mosquito vectors
C. Vishnui, C. pseudovishnui, C. tritaeneorhynchus, C. gelidus are the known vectors of JE virus.

Breeding places of mosquitoes

• Irrigated rice fields (Most important breeding place.)
• Shallow ditches.
• Pools and standing water.

There is no man to man transmission. Man is only an accidental and dead end host. Children below the age 15 are often victims of the disease.

Chandipura Encephalitis
Through Sandflies. (Information of sandflies is given below)

Sandflies are small insects, light or dark–brown in colour. They are smaller than mosquitoes, measuring 1.5 to 2.5 mm in length with their bodies and wings densely clothed with hair. Some 30 species of sand – flies have been recorded in India. The important ones are: Phlebotomus argentipes, P. papatasii, P. sergenti, and Sergentomyia punjabensis. (19).