Abstract
BackgroundPredicting the spatial distribution of pathogens with an environmental stage is challenging because of the difficulty to detect them in environmental samples. Among these pathogens, the parasite Toxoplasma gondii is the causative agent of the zoonosis toxoplasmosis, which is responsible for public health issues. Oocysts of T. gondii are excreted by infected cats in the environment, where they may survive and remain infectious for intermediate hosts, specifically rodents, during months to years. The landscape structure that determines the density and distribution of cats may thus impact the spatial distribution of T. gondii. In this study, we investigated the influences of rural settings on the spatial distribution of oocysts in the soil.MethodWe developed a spatially explicit agent based model to study how landscape structures impact on the spatial distribution of T. gondii prevalence in its rodent intermediate host as well as contamination in the environment. The rural landscape was characterized by the location of farm buildings, which provide shelters and resources for the cats. Specifically, we considered two configurations of farm buildings, i.e. inside and outside a village. Simulations of the first setting, with farm buildings inside the village, were validated using data from previous field studies. Then, simulation results of the two settings were compared to investigate the influences of the farm locations.ResultsModel predictions showed a steeper relationship between distance to the nearest farm and infection levels when farm buildings, and thus cats, were concentrated in the same area than when the farms were spread over the area. The relationship between distance to the village center and level of environmental contamination also differed between settings with a potential increased risk for inhabitants when farms are located inside the village. Maps of the risk of soil contaminated with oocysts were also derived from the model.ConclusionThe agent-based model provides a useful tool to assess the risk of contamination by T. gondii oocysts at a local scale and determine the most at risk areas. Moreover it provides a basis to investigate the spatial dynamics of pathogens with an environmental stage.Electronic supplementary materialThe online version of this article (doi:10.1186/1476-072X-13-45) contains supplementary material, which is available to authorized users.
Highlights
Parasites with environmental stages are often challenging because of the difficulties to detect them in environmental samples [1,2] and to predict their spatial distribution [3,4]
Model predictions showed a steeper relationship between distance to the nearest farm and infection levels when farm buildings, and cats, were concentrated in the same area than when the farms were spread over the area
The relationship between distance to the village center and level of environmental contamination differed between settings with a potential increased risk for inhabitants when farms are located inside the village
Summary
Parasites with environmental stages are often challenging because of the difficulties to detect them in environmental samples [1,2] and to predict their spatial distribution [3,4]. The spatial distribution may depend on environmental factors such as the site topography, the level of rain fall, and the temperature, which may influence transport and survival of these free living stages [5,6,7,8] Many of these parasites are zoonotic pathogens with an environmental stage that can directly infect animals and humans [9]. Predicting the spatial distribution of pathogens with an environmental stage is challenging because of the difficulty to detect them in environmental samples Among these pathogens, the parasite Toxoplasma gondii is the causative agent of the zoonosis toxoplasmosis, which is responsible for public health issues. We investigated the influences of rural settings on the spatial distribution of oocysts in the soil
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