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Group structure, population density and the emergence of Ebola in African Apes.
Walsh, Peter*,1, Wachter, Pauwel2, Marc, Ella Akou2, Huijbregts, Bas2, Idiata Mambounga, Daniel3, Lahm, Sally4, Ndong Obiang, Sosthène 3, White, Lee5, 1 Department of Ecology and Evolutionary Biology, Princeton, NJ, USA2 WWF Central Africa Regional Program Office, Libreville, Estuaire, Gabon3 Ministère de l'Economie Forestière, des Eaux, de la Pêche chargé de l'Environnement et de la Protection de la Nature, Libreville, Estuaire, Gabon4 Institut de Recherche en Ecologie Tropicale, Libreville, Estuaire, Gabon5 Wildlife Conservation Society, Bronx, NY, USA
ABSTRACT- The great majority of the world's gorillas (Gorilla gorilla) and common chimpanzees (Pan troglodytes) live in Western Equatorial Africa (WEA). Over the last decade, an epidemic of what appears to be Ebola hemorrhagic fever has killed a substantial proportion of the gorillas and chimpanzees in WEA. The epidemic continues to burn and the rest of the regional population is at serious risk. Unfortunately, there is very little published information on Ebola transmission dynamics with which to plan management responses. Here we use data on gorilla derived from observations at clearings and extensive nest surveys to test alternative models of Ebola transmission. Our analyses suggest a high rate of virus transmission between gorillas within a group. Results from a spatially explicit, individually based simulation model suggest density dependent transmission dynamics in which Ebola cannot persist below some threshold gorilla population density. Observations on the location of Ebola outbreaks are consistent with this hypothesis as are survey data. Gorilla group size may also have an effect on transmission rate that is independent of local population density. We discuss maximum likelihood estimation of simulation model parameters with both observations from habituated gorillas and nest survey data and describe how the model might be used to evaluate and optimize Ebola management strategies such as vaccination, barrier cutting, and translocation.
Key words: disease, ape, modelling, ebola