Pérez Grégoire

Abstract :

An increase in the emergence or in the reemergence of infectious diseases of human and his domestic animals has been observed in the last decades. Most of these diseases are zoonotic, i.e. originated from wildlife, and imply often a vector for their transmission. At the same time, land use changes linked to agricultural intensification have modified the landscapes. The aim of the thesis was to enhance the state of knowledge on the influence of the landscape on the relationships between hosts, vectors and pathogens.
In Europe, small mammals can be abundant in most of terrestrial ecosystems; they are thus preferred hosts for the generalist tick species Ixodes ricinus. They are also reservoirs of tick-borne infectious agents. The results of this thesis are based on two years of sampling, in spring and autumn, of small mammals and ticks in different landscapes. We analyzed them for three of the infectious agents they host and transmit: Borrelia burgdorferi sensu lato (Lyme disease), Anaplasma phagocytophylum (anaplasmosis) and Theileria (Babesia) microti (piroplasmosis), this last one could not be exploited because of too low prevalence. The 24 sampling sites were half in the core or the edge of a forest and half in agricultural landscapes with a gradient of land cover and of landscape openness.
The best explanatory variable for nymph abundance was the presence of I. ricinus larvae the previous year. The results also indicate a relationship between the number of larvae attached on wood mice (Apodemus sylvaticus ; 76,5% of the catches) and the abundance of nymphs the following year. Bank voles (Myodes glareolus ; 22,3% of the catches) harbored less larvae in spring, certainly because of an acquired resistance to ticks in the overwintering individuals. Despite that these two species react differently to the composition and configuration features of the landscape, the abundances of nymphs were not related to these features. Other hosts, like roe deer (Capreolus capreolus), meteorological and microclimatic factors probably influence the abundances and the distribution of ticks in the landscape.
The host specific richness and the abundance of bank voles, which were threefold more infected than wood mice, likely amplified the prevalence of A. phagocytophylum of these two rodent species. Conversely, landscape fragmentation, via the reduction of host population sizes, seems to act negatively on this prevalence. No clear spatial pattern was observed for B. burgdorferi s.l.. Likewise, no link could be established between the prevalence of the rodents and the prevalence of the nymphs. These results suggest a possible role of more specialist tick species, I. trianguliceps and I. acuminatus, in the circulation of the studied infectious agents, emphasizing the possible interest of considering the
whole vector community in further studies. The results also emphasize the importance of considering a maximum of small mammal reservoir hosts, even at low abundances, at the landscape scale to better understand the transmission of these vector-borne infectious diseases.

Key words :

Agroecosystems, connectivity, ecotones, interactions hosts-vectors-pathogens