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Taking landscape structure into account to better understand the epidemiology of tick-borne diseases

Ticks gorged on the head of a bank vole, one of the most common small rodent species in our agro-ecosystems.  Photo Yann Rantier (OSCAR project).
With several hundred thousand human cases per year, tick-borne diseases are the most important vector-borne diseases in Europe. They involve a wide variety of wild and domestic vertebrate species that are feeding hosts used by ticks for their blood meals but also reservoirs of infectious agents transmitted by these mites. The mosaic of habitats that make up bocage landscapes (forests, hedges, crops, meadows...) influences the spatial distribution of these pathogens. The rate of infection by tick-borne bacteria varies in small rodents sampled at sites with different woodland areas and hedgerow densities. The frequency of anaplasmosis bacteria increased with the proportion of wooded habitat, which in turn correlated with the abundance of woodland mice that are effective reservoirs of this pathogen. For Lyme disease bacteria, the greater the interface between woodland and grassland, the more frequent they are in small rodents. These results illustrate the need to consider community and landscape ecology to better understand the epidemiology of these diseases.

Context :

With several hundred thousand human cases per year, tick-borne diseases are the most important vector-borne diseases in Europe. They involve a wide variety of wild and domestic vertebrate species that are feeding hosts used by ticks for their blood meals but also reservoirs of infectious agents transmitted by these mites. As such, they are emblematic examples for health ecology approaches, illustrating the close links between natural (especially wooded) and anthropised environments and their consequences on the epidemiology of zoonoses. Global changes (global warming, collapse of biodiversity, changes in land use) have a particular impact on them. The ANR OSCAR project (Agricultural Landscape Mapping Simulation Tool for Acarological Risk) focused on the scale of agricultural landscapes to understand these major public health issues.

Results :

We measured the rate of infection with tick-borne bacteria in small rodents sampled in sites with different landscape types characterised by their woodland area and hedgerow density. The frequency of anaplasmosis bacteria increased with the proportion of wooded habitats, which in turn correlated with the abundance of field mice, which are effective reservoirs of the pathogen. For the bacteria responsible for Lyme disease, the greater the interface between woodland and grassland, the more frequent they are in small rodents. However, taking into account the connectivity of woodlands does not improve the statistical models explaining the spatial variability of the frequency of these pathogens in small rodents.

These results illustrate the need to take into account community and landscape ecology to better understand the epidemiology of these diseases.

Perspectives :

Combined with a simulator that generates landscapes with different proportions of different environments (woodland, grassland, crops, hedges, buildings), these studies will allow us to explore the consequences of landscape modifications on mite risk. In addition, we aim to explicitly take into account the movements of hosts, particularly deer, within the mosaic of habitats that these landscapes constitute, in order to better understand how they contribute to tick dispersal at this scale.

Valorisation :

2 articles were published on the theme "landscape and tick-borne diseases" in 2020 (mentioned below) but also in 2018 and 3 in 2017)

Several popular scientific articles and conferences for the general public related to the OSCAR project

Bibliographic references :

Perez, G., Bastian, S., Chastagner, A., Agoulon, A., Rantier, Y., Vourc’h, G., Plantard, O., and Butet, A. 2020. Relationships between landscape structure and the prevalence of two tick-borne infectious agents, Anaplasma phagocytophilum and Borrelia burgdorferi sensu lato, in small mammal communities. Landscape Ecology:718403. https://doi.org/10.1007/s10980-019-00957-x

Lebert I., Agoulon A., Bastian S., Butet A., Cargnelutti B., Cèbe N., Chastagner A., Léger E., Lourtet B., Masseglia S., McCoy K. D., Merlet J., Noël V., Perez G., Picot D., Pion A., Poux V., Rames J.-L., Rantier Y., Verheyden H., Vourc'h G., Plantard O. 2020. Distribution of ticks, tick-borne pathogens and the associated local environmental factors including small mammals and livestock, in two French agricultural sites: the OSCAR database. Biodiversity Data Journal, 8:e50123 doi: 10.3897/BDJ.8.e50123

 

 

Ticks gorged on the head of a bank vole, one of the most common small rodent species in our agro-ecosystems.  Photo Yann Rantier (OSCAR project).