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Changes in biodiversity may impact infectious disease transmission through multiple mechanisms. We explored the impact of biodiversity changes on the transmission of Amazonian leishmaniases, a group of wild zoonoses transmitted by phlebotomine sand flies (Psychodidae), which represent an important health burden in a region where biodiversity is both rich and threatened. Using molecular analyses of sand fly pools and blood‐fed dipterans, we characterized the disease system in forest sites in French Guiana undergoing different levels of human‐induced disturbance. We show that the prevalence of Leishmania parasites in sand flies correlates positively with the relative abundance of mammal species known as Leishmania reservoirs. In addition, Leishmania reservoirs tend to dominate in less diverse mammal communities, in accordance with the dilution effect hypothesis. This results in a negative relationship between Leishmania prevalence and mammal diversity. On the other hand, higher mammal diversity is associated with higher sand fly density, possibly because more diverse mammal communities harbor higher biomass and more abundant feeding resources for sand flies, although more research is needed to identify the factors that shape sand fly communities. As a consequence of these antagonistic effects, decreased mammal diversity comes with an increase of parasite prevalence in sand flies, but has no detectable impact on the density of infected sand flies. These results represent additional evidence that biodiversity changes may simultaneously dilute and amplify vector‐borne disease transmission through different mechanisms that need to be better understood before drawing generalities on the biodiversity‐disease relationship.

In Meriones unguiculatus, the recovery rate of 80 inoculated larvae was low (about 20 %) and irregular. In the natural host Lemniscomys striatus, the recovery rate was about 50 % with ino culated doses of 30, 80 or 400 L3, but slightly higher for 400 L3. This rate was constant from day 2 to month 8 post infection (p. i.). When 7-9 reinoculations were performed in one year, the reco very rate of the late inoculation was of only 14 %.After subcutaneous inoculations, larvae penetrated into the peri pheric lymphatic vessels from hour 6 p. i. and migrated to the lombar and mesenteric lymphnodes ; this first migratory phase was achieved 5 days p. i. Later, the larvae migrated into the digestive tract lymphatic system. Filarial localization did not depend upon the L3 dose: half were found in the caecum and anterior colon (3 cm) wall, and half were distributed in the posterior colon, mesen tery and small intestine. A small number (3-5 %) of the filariae were found in the pulmonary blood vessels, as a result of acci dental migration by the thoracic canal. A similar phenomenon is known in the lymphatic filariae Brugia spp. in rodents and Conispiculum flavescens in a lizard. Several arguments suggest that the genus Monanema is fundamentally lymphatic.Migrations and life of filariae in the lymphatic system seems to be more usual than it is generally admitted. In onchocerciasis, this may at least partially explain the lymphopathology of the inguinal region. Chez Meriones unguiculatus, le taux de développement des larves inoculées est faible (20 % en moyenne) et irrégulier. Chez l'hôte naturel Lemmniscomys striatus, quelle que soit la dose inoculée (30, 80 ou 400 L3), ce taux avoisine 50 % ; toutefois il est légère ment augmenté pour la dose de 400 L3. Le rendement est stable du 2e jour au 8e mois suivant l'inoculation. Sept à 9 réinocula tions faites sur 1 an abaissent à 14 % le rendement du dernier inoculat. A la suite des inoculations sous-cutanées, les larves pénè trent dans les vaisseaux lymphatiques périphériques dès la 6e heure et migrent vers les lymphocentres lombaires et mésentériques ; cette première phase de migration s'achève en 5 jours. Les larves s'enfon cent par la suite progressivement dans le système lymphatique des parois du tube digestif. La répartition des filaires est stable quelle que soit la dose de L3 : la moitié vit dans la paroi du caecum et des 3 cm antérieurs du côlon ; le reste se répartit entre le côlon postérieur, le mésentère et l'intestin grêle. 3-5 % des filaires sont dans les vaisseaux sanguins pulmonaires, à la suite de remontées accidentelles par le canal thoracique. Un phénomène analogue s'observe avec les filaires lymphatiques, Brugia spp. chez les ron geurs et Conispiculum flavescens chez un lézard. Plusieurs argu ments suggèrent que le genre Monanema est fondamentalement lymphatique. Chez les filaires, les migrations et la vie dans le système lymphatique semblent plus générales qu'il n'est couram ment admis. Elles pourraient, dans l'onchocercose, contribuer à expliquer la lymphopathol...

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