The Spread of Tick-Borne Borreliosis in West Africa and Its Relationship to Sub-Saharan Drought

Jean-Francois Trape Laboratoire de Paludologie, Service d'Hydrologie, et Programme Eau et Sante, Institut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Service d'Epidemiologie, Institut Pasteur, Dakar, Senegal

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Bruno Godeluck Laboratoire de Paludologie, Service d'Hydrologie, et Programme Eau et Sante, Institut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Service d'Epidemiologie, Institut Pasteur, Dakar, Senegal

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Georges Diatta Laboratoire de Paludologie, Service d'Hydrologie, et Programme Eau et Sante, Institut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Service d'Epidemiologie, Institut Pasteur, Dakar, Senegal

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Christophe Rogier Laboratoire de Paludologie, Service d'Hydrologie, et Programme Eau et Sante, Institut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Service d'Epidemiologie, Institut Pasteur, Dakar, Senegal

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Fabrice Legros Laboratoire de Paludologie, Service d'Hydrologie, et Programme Eau et Sante, Institut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Service d'Epidemiologie, Institut Pasteur, Dakar, Senegal

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Jean Albergel Laboratoire de Paludologie, Service d'Hydrologie, et Programme Eau et Sante, Institut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Service d'Epidemiologie, Institut Pasteur, Dakar, Senegal

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Yannick Pepin Laboratoire de Paludologie, Service d'Hydrologie, et Programme Eau et Sante, Institut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Service d'Epidemiologie, Institut Pasteur, Dakar, Senegal

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Jean-Marc Duplantier Laboratoire de Paludologie, Service d'Hydrologie, et Programme Eau et Sante, Institut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Service d'Epidemiologie, Institut Pasteur, Dakar, Senegal

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In West Africa, tick-borne relapsing fever is due to the spirochete Borrelia crocidurae and its geographic distribution is classically limited to the Sahel and Saharan regions where the vector tick Alectorobius sonrai is distributed. We report results of epidemiologic investigations carried out in the Sudan savanna of Senegal where the existence of the disease was unknown. A two-year prospective investigation of a rural community indicated that 10% of the study population developed an infection during the study period. Transmission patterns of B. crocidurae to humans and the small wild mammals who act as reservoirs for infection were similar to those previously described in the Sahel region. Examination of 1,197 burrows and blood samples from 2,531 small mammals indicated a considerable spread of the known areas of distribution of A. sonrai and B. crocidurae. The actual spread of the vector and the disease has affected those regions where the average rainfall, before the start of the extended drought in West Africa, reached up to 1,000 mm and corresponds to the movement of the 750-mm isohyet toward the south from 1970 to 1992. Our findings suggest that the persistence of sub-Saharan drought, allowing the vector to colonize new areas in the Sudan savanna of West Africa, is probably responsible for a considerable spread of tick-borne borreliosis in this part of Africa.

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