Abstract
The largest population of the endangered Indian yellow-nosed albatross (Thalassarche carteri) is breeding on Amsterdam Island (French Southern and Antarctic Lands), where it has been declining and experiencing a very high mortality of nestlings over the last decades. Pasteurella multocida, the causative agent of avian cholera, is suspected to be responsible for these mortalities and the use of a vaccine to protect albatross nestlings has been evaluated for a few years. Direct vaccination of the nestlings has been tested, but also a potential protective effect via a transfer of maternal antibodies. The vaccine used was a specifically tailored vaccine (autologous vaccine) developed by Ceva Biovac against a strain of Pasteurella multocida isolated from a dead albatross on the island. Based on promising initial results, the objectives of the thesis were to adjust the vaccination protocol and to improve our knowledge of the eco-epidemiological processes involving vertebrate populations breeding on Amsterdam Island. The work has been based on a close monitoring of breeding individuals within and between years, and on novel experimental data, in particular with the use of a new formulation of the vaccine. We found that a diversity of pathogens was involved in the mortalities and that an optimal age for the vaccination of nestlings is at about 10 days after hatching. We also found evidence that the vaccination of breeding females could protect nestlings against avian cholera over several years. However, the high density of brown rats (Rattus norvegicus) in the bird colony prevented a strong protective effect of the vaccine. These results improve our knowledge of the mechanisms of pathogen circulation in colonial breeding species. In addition, they provide useful elements for assessing the relative benefits expected from different vaccination scenarios. This thesis shows the importance of integrating complementary approaches, particularly from the biomedical field and population ecology, to address issues related to the emergence of infectious diseases in the current context of environmental change.