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Genetic structure of black rat populations in a rural plague focus in Madagascar

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Abstract:

The genetic structure of reservoir populations is a key characteristic in understanding the persistence of infectious diseases in natural systems. In the Highlands of Madagascar, where plague has persisted since 1920, the black rat, Rattus rattus (L., 1758), is the sole species acting as a reservoir of the disease. Ecological surveys have shown a clear correlation between the locations of the plague-persistence area in Madagascar (above 800m elevation) and the distribution area of one endemic plague vector, the flea Synopsyllus fonquerniei, which is found exclusively on rats living outdoors. This clear habitat segregation has led to the suggestion that R. rattus populations in the central highlands are divided into indoor- and outdoor-dwelling populations. Using eight microsatellite markers, we analysed the genetic structure of R. rattus populations living within a human plague focus in relation to habitat and geographic distance. We found that habitat by itself was not a structuring factor, unlike geographic distance. Nevertheless, the significant genotypic differentiation of R. rattus populations that was found at a fine spatial scale might relate to differences in population dynamics between rats in indoor and outdoor habitats.

La structure génétique des populations réservoirs est une caractéristique clef pour comprendre la persistance des maladies infectieuses en milieu naturel. Sur les Hautes Terres malgaches, où la peste persiste depuis 1920, le rat noir Rattus rattus (L., 1758), est la seule espèce qui peut potentiellement servir de réservoir de la maladie. Des études écologiques ont montré une corrélation claire entre la localisation de la zone de persistance de la peste à Madagascar (au-dessus de 800m d’altitude) et l’aire de distribution d’une puce endémique vecteur de la peste, Synopsyllus fonquerniei, qui parasite exclusivement les rats vivant à l’extérieur des maisons. Une telle ségrégation d’habitat a conduit à formuler l’hypothèse selon laquelle les rats des Hautes Terres sont structurés en populations d’extérieur et d’intérieur. En utilisant huit marqueurs microsatellites, nous avons analysé la structure génétique des populations naturelles de rats d’un foyer humain de peste en relation avec l’habitat et la distance géographique. Nous avons trouvé que l’habitat en lui-même n’est pas un facteur explicatif de la structure génétique, au contraire de la distance géographique. La différenciation génotypique significative des populations à une échelle spatiale fine pourrait en revanche indiquer des dynamiques de populations différentes chez les rats vivant à l’intérieur et à l’extérieur des maisons.

Document Type: Research Article

Publication date: September 1, 2007

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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