MO3

Vector-borne diseases (dengue, Zika, chikungunya) are an important public health issue. Understanding their transmission dynamics remains a major challenge at the sub-urban level. Indeed, environmental heterogeneities, variations in vector densities and daily mobility constitute a lock on the definition of epidemic risk indicators at this scale. MO3 therefore aims to (i) develop a simulation model to study the sensitivity of epidemic dynamics to targeted scenarios of anti-vector fights and (ii) evaluate in a large metropolis where dengue is endemic, Bangkok (Thailand), the effectiveness of these strategies. In cities where these diseases are endemic, our first hypothesis is that the urban territory has a limited number of places favorable to the maintenance of mosquito population during the inter-epidemic season, sufficient to ensure local, continuous and low-noise circulation of viruses. With seasonal changes (rising temperatures, monsoon rains), vector populations are exploding, increasing the risk of spreading viruses from these areas. Our second hypothesis is that the structuring of urban space (residence, economic and commercial activities, vegetated spaces) and the resulting discontinuities structure the daily mobilities of populations, and potentially the spread of pathogens in epidemic proportions. It is therefore essential to identify these potential reservoirs of pathogen diffusion early. Moreover, in cities where these diseases are not endemic, or not yet present, the dynamic mapping of the environmental risk based on the ecology of the mosquito must make it possible to identify and monitor the places and the periods favorable to the implantation and the proliferation of mosquito vectors. To achieve these objectives, the MO3 project will rely on differential equations and agent-based model, with high spatial and temporal resolution, to describe finely the urbanized space and the variety of dynamics that unfold there, those of vectors and human populations. Vector dynamics will be influenced by the spatial and temporal heterogeneity of their ecological niche, those of humans by their daily mobility, partly linked to their place of residence, their socio-economic profile and their age. The calibration of the model will be based on various data: satellite images, census, social networks, vector and epidemiological retrospective data. We also plan field surveys. Sites will be selected according to a value gradient of the ecological niche of the vector and a value gradient of centrality of the places. Weekly surveys over a 2-year period will be used to analyze the evolution of adult mosquito stocks with respect to these two indicators, and epidemiological surveys of at-risk populations will be used to assess exposure levels, according to these two indicators. All of this data will also be used to calibrate and validate the simulation model. Exploration methods based on evolutionary algorithms will be mobilized to evaluate, compare and hierarchize the mechanisms of the model with regard to simulated dynamics and observations that they can or must produce or reproduce. These methods will also evaluate and compare vector control strategies against the epidemiological dynamics simulated by the model, in search of the most effective strategy or strategies. MO3's ambition is therefore to develop a generic method that allows for vector-based struggles in priority areas, thus enabling local actors to optimally allocate their available but limited resources.