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Abstract. Gaining a better understanding of the spatial population structure of infectious agents is increasingly recognized as being key to their more effective mapping and to improving knowledge of their overall population dynamics and control. Here, we investigate the spatial structure of bancroftian filariasis distribution using geostatistical methods in an endemic region in Southern India. Analysis of a parasite antigenemia prevalence dataset assembled by sampling 79 villages selected using a World Health Organization (WHO) proposed 25 × 25 km grid sampling procedure in a 225 × 225 km area within this region was compared with that of a corresponding microfilaraemia prevalence dataset assembled by sampling 119 randomly selected villages from a smaller subregion located within the main study area. A major finding from the analysis was that once large-scale spatial trends were removed, the antigenemia data did not show evidence for the existence of any small-scale dependency at the study sampling interval of 25 km. By contrast, analysis of the randomly sampled microfilaraemia data indicated strong spatial contagion in prevalence up to a distance of approximately 6.6 kms, suggesting the likely existence of small spatial patches or foci of transmission in the study area occurring below the sampling scale used for sampling the antigenemia data. While this could indicate differences in parasite spatial population dynamics based on antigenemia versus microfilaraemia data, the result may also suggest that the WHO recommended 25 × 25 km sampling grid for rapid filariasis mapping could have been too coarse a scale to capture and describe the likely local variation in filariasis infection in this endemic location and highlights the need for caution when applying uniform sampling schemes in diverse endemic regions for investigating the spatial pattern of this parasitic infection. The present results, on the other hand, imply that both small-scale spatial processes and large-scale factors may characterize the observed distribution of filariasis in the study region. Our preliminary analysis of a mountain range associated large-scale trend in the antigenemia data suggested that a nonlinear relationship of infection prevalence with elevation might be a factor behind such observed global spatial patterns. We conclude that geostatistic methods can provide a powerful framework for carrying out the empirical investigation and analysis of parasite spatial population structure. This study shows that their successful application, however, will crucially depend on our gaining a more thorough understanding of the appropriate geographic scales at which spatial studies should be carried out.

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Aedes aegypti and Aedes albopictus are known vector mosquitoes for several emerging arthropod-borne viruses (arboviruses) including dengue fever, chikungunya, Zika fever, Mayaro and yellow fever viruses across the world. Aedes species vector mosquitoes are blamed for the spread of dengue and chikungunya in India. Dengue and Chikungunya is the illustrious public health problems in the country, dengue has public health importance and cumulative burden to the affected community, especially in the Southern States of India, since 1991, and followed by the highest outbreaks of chikungunya in the Southern India, 2006. Dengue cases reported from 24 States and 3 Union Territories out of 34 States / Union Territories in India, and highest reports recorded in 5 major States (Tamil Nadu, Kerala, Karnataka, Punjab and West Bengal), during 2017. All the four serotypes of dengue virus (DEN-1, DEN-2, DEN-3, and DEN-4) are detected across the country various with space and time. Mapping the geographical distribution and seasonal variation of dengue and chikungunya vector mosquitoes (Aedes aegypti and Aedes albopictus) is absolutely significant for the systematic surveillance, organization, and implementation, accordingly, the public health authority possibly will make prevention measures to control the dengue epidemic earlier in advance and monitoring the endemic situation in the state as well as in the country, continuously [16,17,18]. Aedes aegypti and Aedes albopictus vector mosquito's density caused by the man-made containers (socio-economic variables), and the natural breeding habitats , and land use / land cover types, environmental risk factors, and climate determinants. All the four serotypes of dengue virus (DEN-1, DEN-2, DEN-3, and DEN-4) are reported in India. The study has mainly focused on the major endemic districts in India, where the state of endemic has accumulative problems, and is grumbling the community. Aedes aegypti and Aedes albopictus are the known vector mosquitoes of dengue and chikungunya. The endemic districts have unique landscape terrain and land use / land cover pattern, and climate factors (precipitation, temperature, relative humidity, and saturation deficiency). The major landscape terrain has hilly, plain and coastal areas. The epidemic areas receive rainfall by both the southwest monsoon and the northeast monsoon from April to November (almost 8 months), and has the average temperature range of 22°C to 31°C, and relative humidity of 70 % to 90 %, and the present study contains the vector density is highly influenced by the maximum number of rainy days, and the occurrences of dengue epidemics clustered regions in India mainly where it receives annual mean rainfall ranging from 300 mm to 1200 mm. The spatial distribution and seasonal variation of vector mosquitoes (Aedes aegypti and Aedes albopictus) in the identified endemic districts are absolutely griping the situation by seasonal variation in precipitation and temperature, land cover spatial variations, socioeconomic , and ecological differen...