Japanese viral encephalitis

Japanese Encephalitis : Is Routine Immunization Required?

Japanese encephalitis is the leading cause of viral encephalitis in Asia. In endemic areas annual incidence ranges from 10-100 per 100000 population. Case fatality averages 30% and a high percentage of the survivors are left with permanent neuropshychiatric sequelae. There is no effective drug treatment for this disease. In recent decades, Japanese encephalitis virus has caused epidemics in previously unaffected countries like India, Myanmar, Nepal, Sri Lanka, Thailand and Viet Nam. No effective environmental control is known. Although socioeconomic improvement and changes in agricultural practices are likely to reduce viral transmission, large-scale vaccination of affected populations with an effective and affordable vaccine appears logical at least in the short term. The impact of large-scale Japanese Encephalitis vaccination is documented in some regions of China and systematic vaccination has contributed to significant decline in incidence in Japan, Republic of Korea and Thailand.

Shifting epidemiology of Flaviviridae

The dengue, West Nile, Japanese encephalitis and yellow fever viruses are important mosquito-borne viruses whose epidemiology is shifting in response to changing societal factors, such as increasing commerce, urbanization of rural areas, and population growth. All four viruses are expanding geographically, as exemplified by the emergence of West Nile virus in the Americas and Japanese encephalitis virus in Australasia. The large, recent global outbreaks of severe neurological disease caused by West Nile virus, the increasing frequency of dengue hemorrhagic fever outbreaks in the Americas, and the emergence of yellow fever virus vaccination-associated viscerotropic disease, are new clinical epidemiologic trends. These worrisome epidemiologic trends will probably continue in coming decades, as a reversal of their societal and biological drivers is not in sight. Nevertheless, the substantial reductions in Japanese encephalitis virus incidence resulting from vaccination programs and economic development in some Asian countries provide some encouragement within this overall guarded outlook.