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JAPANESE ENCEPHALITIS

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This is another Flavivirus that occurs throughout Asia since 1871. In 1924 an outbreak surged in Japan that spread all over the islands with over 12-thousand cases from 1924 to 1933 (Matheson 1950). The mortality rate was very high at around 65 percent.

The transmission cycle involves mosquitoes biting water birds such as herons, egrets and ibises, which are the main reservoir hosts. Some infected mosquitoes also draw blood from pigs, which develop high viraemia and are thus amplifying hosts (Service 2008). When infected mosquitoes bite birds or pigs and later bite humans they can transmit the virus. Humans are dead-end hosts and thus there is no human-to-human transmission.

Vectors that transmit to birds, humans and pigs are the rice-field Culex tritaeniorhynchus, Culex vishnui and Culex pseudovishnui. Culex gelidus that breeds in streams and rice field is also a vector and is thought to maintain the virus in pig-to-pig transmission. In southern India Mansonia indiana behaves as a secondary vector.

Japanese Encephalitis - Life Cycle

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Key References: <medvet.ref.htm> <Hexapoda>

Matheson, R. 1950. Medical Entomology. Comstock Publ. Co, Inc. 610 p.

Service, M. 2008. Medical Entomology For Students. Cambridge Univ. Press. 289 p

Legner, E. F. 1995. Biological control of Diptera of medical and veterinary importance. J. Vector Ecology 20(1): 59_120.

Legner, E. F.. 2000. Biological control of aquatic Diptera. p. 847_870. Contributions to a Manual of Palaearctic Diptera,

Vol. 1, Science Herald, Budapest. 978 p.