**5. Transmission**

The JE virus exists in a zoonotic transmission cycle between mosquitoes and pigs and/or water birds; humans get infected only accidentally when bitten by an infected mosquito [Fig 3] and are a dead-end host [Gould *et al*., 2008]. JEV has been isolated from many mosquito species in field studies, and even though the major mosquito vectors differ in diverse geographical regions, the most important is *Culex tritaeniorhynchus*. For Eastern Asia, Southern Asia and Southeastern Asia, the chief vector is *C. tritaeniorhynchus* [Rao *et al*., 2001]. For Northern Australia, the chief vector is *C. annulirostris.* From India's outlook, there are several other secondary vectors such as *Anopheles peditaeniatus*, *A. subpictus, C. epidesmus, C. gelidus, C. pseudovishnui, C. whitemorei, Mansonia uniform* and *M. Indiana* [Borah *et al*., 2013]. Pigs are the key component in the transmission cycle with respect to human infection, while egrets, herons and other ardeid birds are significant maintenance hosts [Hecker *et al*., 2013; Sarkar *et al*., 2013]. Of other vertebrates, horses can develop CNS infection but are a dead-end host; Other domestic animals may also get infected, but do not show any evidence of viremia. Rodents are refractory to infection; and amphibians, bats and reptiles can be infected experimentally and virus can persist, but the role of these species in hibernating and maintaining the virus in the environment is undisclosed.

There are two epidemiological forms of transmission: an endemic form in tropical areas with virus circulation almost throughout the year, but with a wide seasonal peak probably due to irrigation practices; and an epidemic form in more temperate areas with clear summer seasonality [Schuh *et al.,* 2013; Gao *et al*., 2013]. Subsequently, JE is mainly a rural disease, where *Cx. tritaeniorhynchus* mosquitoes breed in rice paddies and pigs provide the main source of blood meals, with the consequence of transmission cycles in close proximity to human habitation.

antigens in the CNS. Histopathology inspection is also very obliging for clinical association and diagnosis of JEV. Diagnosis is accordingly targeted towards the detection of antibodies in serum and cerebrospinal fluid. Cases like cross-reactivity of antibodies to other flaviviruses cause confusion in the diagnosis of JEV. IgM capture ELISA has been the most extensively used diagnostic method for JE detection [Hobson-Peters *et al*., 2012; Palani *et al*., 2013; Borthakur *et al*., 2013]. Currently, dipstick method, JEV-CheX and reverse transcriptase PCR are some of the methods which are used for the early detection of JEV [Yang *et al.,* 2013; Seo

**Figure 3.** Transmission cycle of Japanese encephalitis virus. Infected Culex mosquitoes (vectors) play the role in the spread of JEV. Pigs are the amplifying hosts and birds (egrets) are the maintenance hosts while humans are the dead-

Japanese Encephalitis: A Neglected Viral Disease and Its Impact on Global Health

http://dx.doi.org/10.5772/58529

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Immunogold Silver Staining (IGSS) Antigens in mononuclear cells peripheral blood and CSF

*et al*., 2013; Zheng *et al.,* 2013].

end hosts.

**Diagnostic tool Detects**

Hemagglutination test Antigens in CSF MAC-ELISA IgM antibodies Dipstick method, JEVCheX Antibodies

**Table 2.** Laboratory diagnostic tools for Japanese encephalitis

RT-PCR, RT-LAMP Universal oligonucleotide primers
