Mémoire

Abstract

Since their discovery in 1994, marine Brucella spp. have been isolated from a wide variety of marine mammals. The B. ceti strain infects cetaceans, while B. pinnipedialis is found in pinnipeds, although cross-infections can occur. Apart from abortions they can cause, these Gram-negative facultative intracellular bacteria are not directly responsible for the death of the individual, but can cause infections and lesions in various organs, which can weaken the animal. The transmission of marine Brucella spp. in these animals has not been fully elucidated, but there is evidence that they can contract brucellosis by vertical, horizontal, and vectorial transmission via parasites, in particular pulmonary nematodes carrying the bacteria. The latter route involves considering the life cycle of these lungworms, as the first-stage larvae, which are also likely to be infected, can contribute to the transmission of Brucella spp. in the marine ecosystem. The aim of this study is therefore to confirm the transmission of Brucella spp. by lungworm larvae in marine mammals, by checking whether the first-stage larvae infesting the lungs of brucellosis-positive individuals are also infected by the bacteria. In total, the lungs of nine individuals of interest (seven positive and two negative for brucellosis) were used, from which fragments were washed to recover as many larvae as possible. The larvae were then concentrated and filtered, making them easier to pipette. A PCR was then carried out on the DNA extracted from these larvae to detect the possible presence of Brucella spp. and thus confirm a possible infection. Of the seven individuals tested positive for brucellosis, four contained larvae probably carrying Brucella spp. However, one of the two individuals tested negative for brucellosis had pulmonary larvae that tested slightly positive. The results obtained in this study support the hypothesis of vectorial transmission by lungworms in marine mammals, already mentioned by several authors. This validates the methodology used in this study to attempt to determine the role of pulmonary nematodes in the transmission of marine Brucella spp. in the marine ecosystem, although it does have some limitations.