Forecasting Spatial Distribution of Japanese Encephalitis Occurrence- A Remote Sensing and GIS Based Study in Assam, India

Abstract

Japanese Encephalitis (JE) is one of the dreaded mosquito borne viral diseases mostly prevalent in South Asian countries including India. It is important to study the detail of the JE affected areas in terms of environmental and social factors that determines the outbreak of the disease. A comprehensive study was conducted during the period 2003-2007 in Dibrugarh, a JE endemic district of Assam. Effect of landscape and socio-economic factors on mosquito vector density was investigated with remote sensing and Geographic Information System (GIS) inputs and developed the methodology for predicting spatial distribution of occurrence JE in the district. The methodology was validated during subsequent 5 years (2008-2012) and accuracy of forecasts has been assessed. Wetlands have been found to be the most preferred habitat type for majority of the JE transmitting mosquitoes followed by paddy growing areas and ponds. Based on the spatial distribution of habitat types, villages in the district divided into three categories of vector abundance and hence the risk of JE. Among socio-economic determinants, pig rearing habitat of the villagers have been found to be most significant. Based on the pig rearing distribution pattern in the village, all the villages have been categorized into three categories of JE virus reservoir abundance viz. high, medium and low. Along with these two categorization approaches, villages were also categorized into three relative scale based on retrospective data on disease intensity. Final JE risk map was prepared with integration of vector abundance map with the map of host abundance and retrospective disease intensity in GIS domain. JE risk maps were prepared at the beginning of the disease season that is at the beginning of April for past five years (2008-2012). Actual cases occurred in the district was overlaid on the JE risk map to verify the accuracy of forecasts. It has been observed that about 70-81% JE cases reported from the High JE risk areas identified under the study during past five years (2008-2012).