Estimated Global Incidence of Japanese Encephalitis: A Systematic review/Estimation De L'incidence Mondiale De L'encephalite Japonaise: Une Evaluation Systematique/ Incidencia Global Estimada De la Encefalitis Japonesa: Una Revision Sistematica

TL;DR: In this paper, the authors present a review of Japanese encephalitis (JE) in Asia, focusing on rural and suburban areas where rice culture and pig farming coexist.

Abstract: Introduction Japanese encephalitis (JE) is among the most important viral encephalitides in Asia, especially in rural and suburban areas where rice culture and pig farming coexist. (1-3) It has also occurred rarely and sporadically in northern Australia and parts of the Western Pacific. (4-6) JE is due to infection with the JE virus (JEV), a mosquito-borne flavivirus. The main JEV transmission cycle involves Culex tritaeniorhynchus mosquitoes and similar species that lay eggs in rice paddies and other open water sources, with pigs and aquatic birds as principal vertebrate amplifying hosts. (1,2,7) Humans are generally thought to be dead-end JEV hosts, i.e. they seldom develop enough viremia to infect feeding mosquitoes. Fewer than 1% of human JEV infections result in JE. Approximately 20-30% of JE cases are fatal and 30-50% of survivors have significant neurologic sequelae. (8) JE is primarily a disease of children and most adults in endemic countries have natural immunity after childhood infection, but all age groups are affected. In most temperate areas of Asia, JEV is transmitted mainly during the warm season, when large epidemics can occur. In the tropics and subtropics, transmission can occur year-round but often intensifes during the rainy season. (1-3) The global incidence of JE is unknown because the intensity and quality of JE surveillance and the availability of diagnostic laboratory testing vary throughout the world. Countries that have implemented high-quality childhood JE vaccination programmes have seen a dramatic decline in JE incidence. Although JE is reportable to the World Health Organization (WHO) by its Member States, reporting is highly variable and incomplete. In the late 1980s, Burke and Leake estimated that 50 000 new cases of JE occurred annually among the 2.4 billion people living in the 16 Asian countries considered endemic at the time (approximate overall annual incidence: 2 per 100 000). (2) In the intervening two decades, despite major population growth, urbanization, changes in agricultural practices and increased use of the JE vaccine in many countries, this figure has been widely quoted, including very recently. (9-13) In 2000, assuming an annual, age-group-specific incidence of 25 cases per 100 000, Tsai estimated that in the absence of vaccination 175 000 cases of JE would occur annually among Asian children aged 0-14 years living in rural areas. (14) The current study used more recent, published, local or national incidence estimates and current population data to produce an updated estimate of the annual global incidence of JE. Methods We approximated the JE-affected territory of each of the 24 countries endemic for JE using a recent update (15) of an earlier approximation by Tsai (16) with some modifications (Table 1, available at: http://www.who.int/bulletin/ volumes/89/10/10-085233). Based on these same approximations, (15,16) we then stratified the JE-affected territory of some countries (e.g. China excluding Taiwan, India and Nepal) into two or more incidence strata. Because suitable studies of JE incidence were not available for every endemic country or incidence stratum, we sorted JE-endemic countries and incidence strata into 10 incidence groups (A, B, C1, C2 and D through I) based primarily on geographic proximity, ecologic similarity, vaccine programme similarity. Table 1 briefly describes the status of each endemic country's JE vaccination programme as of 2009, according to recent publications and unpublished sources. (8,17-20) Incidence data We identified studies that contained potentially useful data on the incidence of JE in Asia in a manner similar to the one used in a recent study of global typhoid fever incidence. (21) Whenever possible, this review followed the relevant guidelines for Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). (22) The review process is described as follows and no protocol is available. …