Metapopulation epidemic model of Rickettsia rickettsii dynamics in a spatially structured population of capybaras

Abstract

Brazilian spotted fever, caused by the bacteria Rickettsia rickettsii is the deadliest spotted fever of the world. R. rickettsii infection has a complex transmission cycle, involving different subpopulations of amplifier hosts and vectors. Modeling these types of complex pathogens represents a challenge in terms of the modeling structure and the extrapolation of insights in policy-related questions. To overcome this challenge, we previously construct a seasonal semi-discrete stochastic model of the R. rickettsii transmission between the tick vector Amblyomma cajennense and the amplifier host Hydrochoerus hydrochaeris. We model the infection among different subpopulations, however we assume the space homogeneous, and so do not include spatial variation. We found that a single infected capybara with at least one infected tick attached is enough to trigger the disease in a non-endemic area. Thereby, we concluded that to avoid the R. rickettsii propagation is necessary to impede the migration of capybaras from endemic areas. Because of the high risk of {R. rickettsii dissemination due to: 1) the actual increase in the availability of food sources (sugar cane crops), near watercourses, that increases the habitat carrying capacity and consequently increase the population of susceptible capybaras, 2) the wide distribution of the vector A. cajennense in the state of São Paulo, 3) the fact that a single infected capybara with at least one infected tick attached is enough to trigger the disease in a non-endemic area, 4) the constant availability of water sources in São Paulo and, 5) the usual migratory behavior of capybaras through water sources; this project aims to model the spatial structure of capybaras in terms of a metapopulation network formed by water sources to gain better insight into the spread of the R. rickettsii and predict future epidemic outcomes. We will create different scenarios to evaluate the effectiveness of random (non-strategic) and targeted (strategic) epidemic interventions for spatially separated patches in the metapopulation model. The strategies will be focus on the amplifier hosts in order to disappear the R. rickettsii infection in groups of A. cajennense. The results of this work will allow the formulation of a public action to the prevention of human cases of Brazilian Spotted Fever based on the manage the population of capybaras. This work also will open the path to further mathematical and computational studies of the dynamics of vector-borne systems.