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Facteurs environnementaux de variation de l'abondance des tiques Ixodes ricinus dans des zones d'étude modèles en Auvergne

Abstract : Enhancing the knowledge and control of risks linked to tick-borne pathogens, in particular to Ixodes ricinus-borne, is one of the public health concerns in France. Tick-borne diseases are also an important issue in veterinary medicine, especially for cattle. In this context, eco-epidemiological studies were conducted in Auvergne by the Animal Epidemiology research unit of the French National Institute for Agricultural Research (INRA), with the support of the "Conseil Régional d'Auvergne", in two bocage (enclosed pastureland) model zones located in the Combrailles ("département du Puy-de-Dôme") and the West Cantal ("département du Cantal") regions. Since nymphs represent the most important stage for pathogen transmission to humans, environmental factors (weather, landscape, hosts) characterizing I. ricinus nymph abundance questing on the vegetation were first studied. Nymphs were drag sampled at the inner perimeter of 61 grazed permanent pastures in 2003 in the Combrailles, and analyzed using a probabilistic modeling approach based on the negative binomial distribution. The reproducibility of the significant factors found in this study was evaluated by testing them with abundance of questing nymphs sampled in different years (2004 and 2006) and location (West Cantal). The main outlined factors, consistent across all studies, were related to the presence of bushes or trees, the presence of woodland and the nymph abundance in the nearest woodland. Thus, we hypothesized that immigration from neighbouring woodland was critical for the maintenance of tick populations on pastures. In a second step, variation factors of I. ricinus larva burden on small mammals at the pasture-woodland ecotone were investigated in 2005 thanks to trapping sessions. The wood mouse (Apodemus sylvaticus) appeared to be the main small mammal species able to transport tick larvae between woodlands and pastures and act as an "epidemiological bridge". In conclusion, I. ricinus tick-bite risk was refined in Auvergne as a first step to assess tick-borne disease risk. The next steps will address: i) the variation of tick infection rate by bacterial pathogens (i.e. Borrelia burgdorferi s.l. - Lyme disease agent, Anaplasma phagocytophilum - human and animal granulocytic anaplasmosis, and Rickettsia spp. of the spotted fever group), and ii) the disease risk factors for the corresponding diseases. Overall, this Ph.D. presented here has fostered methodological and strategic discussions regarding biologic or biostatistic issues.
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Chloé Boyard. Facteurs environnementaux de variation de l'abondance des tiques Ixodes ricinus dans des zones d'étude modèles en Auvergne. Biologie animale. Université Blaise Pascal - Clermont-Ferrand II, 2007. Français. ⟨NNT : 2007CLF21813⟩. ⟨tel-00930307⟩

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