Mobility and non-household environments: understanding dengue transmission patterns in urban contexts
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Households (HH) have been traditionally described as the main environments where people are at risk of dengue (and other arbovirus) infection. Mounting entomological evidence has suggested a larger role of environments other than HH in transmission. Recently, an agent-based model estimated that over half of infections occur in non-household (NH) environments like workplaces, markets, and recreational sites. However, the importance of human and vector mobility and the configurations of urban spaces in mediating the effects of NH on dengue transmission remains understudied. To improve our knowledge of the relevance of these spaces in transmission, we expanded an agent-based model calibrated from field data in Kenya to examine movement of people and vectors under different spatial configurations of buildings. In this model, we assessed the number of people traveling between HH and NH, their distance, and the number of mosquitoes migrating. Those were studied on three different urban configurations, on which the NH are spatially distributed either randomly (scattered), centered (in a single center), or clustered (in more than one cluster). Across simulations, the number of people moving is a major influential variable where higher levels of movement between HH and NH increases the number of cases. In addition, the number of cases is higher when NH are scattered. These results highlight the importance of NH in transmission as a major spreader of infections between households. In addition, we found an inverse relationship between mosquito migration and population size and hence transmission, which underscores the high cost of migration for mosquitoes. Intriguingly, the distance that people travel from HH to NH seems to have little effect on dengue burden; however, it affects the level of spatial clustering of cases. The results of this work support the relevance of NH in transmission and its interaction with human movement in driving dengue dynamics.
Author summary
Recent evidence describes a major role of non-household (NH) environments in dengue transmission. This new knowledge implies that spatial distribution of these locations and the movement of both vectors and humans among them has implications in dynamics of transmission. However, these haven’t been evaluated neither together nor considering a differential role in transmission of urban environments. We modified a previously informed agent-based model to include spatial variables by assessing three different urban conformations, i.e. when NH are randomly distributed (scattered), centered, or grouped in differed clusters (clustered). On these, we also evaluated the movement of both vectors and people from households (HH) to NH (both distance and number of individuals). Our findings, which includes a higher burden of dengue when NH are scattered and at higher levels of human movement and low level of vector migration, are aligned with the idea that infections are mainly happening in NH mediated by human mobilization. Infected people reach the households where local subpopulation of vector spread the virus to remaining inhabitants. This work highlights the role of NH and human mobility in dengue transmission.
