Describing and understanding factors affecting the distribution and circulation of infectious agents in animal populations is important for basic and applied reasons. Populations of wild vertebrates living in southern polar areas are increasingly the subject of threats from infectious diseases, which can add to other environmental threats, and it is becoming critical to establish baseline data and sound understanding of the dynamics of host-parasite interactions in these systems. In some instances, such information can have clear potential management implications. Populations of vertebrates breeding in colonies are especially important to study in those respects because they are distributed in very discrete units among and within which the transmission of infectious agents can be affected by various processes and can lead to disease outbreaks than can affect hundreds to thousands of individuals at the same time. In this project, we plan to continue to explore how large scale dispersal processes and more local interactions between hosts and parasites can affect the dynamics of circulation of infectious agents and the occurrence of possible outbreaks. In order to do so, we will combine complementary methodological approaches from different fields, involving notably laboratory analyses of biological samples gathered in the field on identified individuals as part of long term observational monitoring, the implementation of specific field experiments (notably using vaccination) and the parallel development of modelling approaches. Modern molecular technics as well as tracking devices will be used to address specific questions. An anthropology approach to questions relating eco-epidemiological processes, biosecurity issues and biodiversity conservation will also be developed. The project will rely the results obtained by our team over the last years, notably on avian cholera on Amsterdam Island, and on the existing set of long-term IPEV research programs conducted on various key sites. The work will continue to be conducted in tight coordination with the TAF National Nature Reserve, with specific aspects which have been integrated in the Plan National d’Action Albatros d’Amsterdam and the Plan de Gestion of the Reserve. A specific focus will continue to be developed on infectious agents potentially responsible for large outbreaks, such as avian cholera, as well as on seabird ticks and tick-borne disease agents. In the context of the plan of eradication of introduced mammals from Amsterdam Island, a quasi-experimental approach will be conducted on the effects of rats on eco-epidemiological dynamics. Field work is planned to be conducted on the three districts of the French sub-Antarctic islands (Amsterdam, Kerguelen and Crozet), but also in other sub-Antarctic areas, in order to address issues at local but also broad spatial scales.