Abstract
Limited surveillance programs and lack of diagnostic laboratory testing capacity in many low and middle income Asian countries have made it difficult to validate epidemiological patterns and anticipate future changes in disease risk. In this study, we consider the case of Japanese Encephalitis in Asia and examine how populations of human hosts and animal reservoirs are expected to change over the next three decades. Growth was modelled at the sub-national level for rural and urban areas to estimate where high-density, susceptible populations will potentially overlap with populations of the virus' amplifying host. High-risk areas based on these projections were compared to the current distribution of Japanese Encephalitis, and known immunization activities in order to identify areas of highest priority for concern. Results indicated that mapping JE risk factors at the sub-national level is an effective way to contextualize and supplement JE surveillance data. New patterns of risk factor change occurring in Southeast Asia were identified, including around major urban areas experiencing both urbanization and growth in pig populations. A hotspot analysis of pig-to-population ratio found a significant spatial cluster extending northward through Southeast Asia and interior China. Mapping forecasted changes in risk factors for JE highlights regions vulnerable to emerging zoonoses and may be an important tool for developing effecting transnational health policies.
Highlights
Japanese Encephalitis (JE) is the leading cause of viral encephalitis in Asia [1, 2]
We propose a method that compensates for under-reporting using demographic trends as a forecasting tool
Rice agriculture areas provide ideal habitat for Culex mosquitoes, and risk of acquiring the virus tends to increase with proximity to paddy fields [10, 11]. [12] estimated that area dedicated to rice agriculture in Asia increased by 22% during the period 1963–2003, which has directly contributed to habitat expansion of Culex mosquitoes
Summary
Japanese Encephalitis (JE) is the leading cause of viral encephalitis in Asia [1, 2]. Rice agriculture areas provide ideal habitat for Culex mosquitoes, and risk of acquiring the virus tends to increase with proximity to paddy fields [10, 11]. [12] estimated that area dedicated to rice agriculture in Asia increased by 22% during the period 1963–2003, which has directly contributed to habitat expansion of Culex mosquitoes. Wading birds from the family Ardeidae (herons, bitterns, and egrets) are a natural reservoir for the virus These birds require shallow water bodies as feeding grounds [13] and frequent areas dedicated to rice agriculture. The distribution of risk factors related to pig husbandry, mosquito life cycle development and habitat, and interactions between hosts and vectors is extremely difficult to track over large areas.
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