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Ticks are considered to be the main vectors of infectious agents in Europe (especially for Lyme disease). The most frequent species in Europe -Ixodes ricinus- is primarily a forest tick, but it is also found in hedgerows on the edges of meadows and heathlands where it parasitizes a wide variety of wild (rodents, birds, deer, etc.) and domestic (cattle, sheep, etc.) hosts.
The risk of contracting tick-borne diseases depends on the interactions between vertebrate hosts, ticks and pathogens. The abundance of each and their relationships depend strongly on the landscape configuration.

The OSCAR programme, funded by the ANR, brought together five laboratories : BioEpAR (Inra-Oniris in Nantes), le CEFS (Inra Occitanie-Toulouse), EcoBio (CNRS, Univ. Rennes1), EPIA (Inra-VetAgro Sup in Clermont-Ferrand), MIVEGEC (CNRS, Univ.Montpellier, IRD). Its objectives were :

• analyze host abundance and distribution and their interaction with ticks,
• to analyse the distribution of the acarological risk (density of infected ticks),
• to better understand the spatio-temporal dynamics of tick populations,
• develop predictive maps of acarological risk based on scenarios of changes in landscape structure.

Field studies combined with laboratory investigations

	The five laboratories involved collected field information in two study areas: the Zone Atelier Armorique and the Vallons et Coteaux de Gascogne, which correspond to different levels of forest fragmentation and land use. Three types of habitats were targeted in each of these areas as they are known to be the most favourable for ticks: forest cores, forest and woodland edges and hedgerow-edged meadow edges. In order to estimate their density, 7900 tick harvests were carried out and those were also the abundance of the hosts: cattle, small mammals (captured using toggle traps with dormitory boxes) deer (located using GPS collars) but also the characterization of the different living places (vegetation, climate...) that were studied. In the laboratory, DNA extracts from ticks (4500 out of 12500 harvested) and blood samples taken from captured mammals were used to search for three pathogens (Anaplasmaspp., Borreliaspp. and Babesiaspp.) in order to assess their spread.	Ticks collected thanks to the flag technique: a large white cloth dragged over the vegetation. © Inra Deer equipped with a GPS collar © Inra

Landscape, a key role in the spread of pathogens by ticks

^{© Inra}

The analysis of tick densities on vegetation showed strong variations at the landscape scale and between the seasons studied from 2012 to 2014. For example, ticks are less present at the edge of pastures when hedges are very small. The study also shows that landscape structure influences rodent populations. A dense network of hedgerows and groves is more favourable to one species (Wood Mouse), while another (bank vole) will be more present in isolated habitats. Moreover, the abundance of these rodents in a given year partly determines the abundance of ticks observed the following year.

The probability of host and tick encounters, a key element in the spread of pathogens, therefore varies greatly in space and time.

The presence of pathogens in ticks varies according to their hosts

In addition, not all hosts, as reservoirs, have the same ability to multiply and maintain pathogens. Deer multiply the bacteria responsible for Lyme disease very poorly while some rodents multiply them efficiently.

Laboratory research has also revealed that the three pathogens studied are present in only 2-5% of the ticks harvested.

The impact of global changes, put into perspective in the OSCAR project, also plays a role in the dynamics of ticks, whose development depends on temperature, hygrometry, changes in landscapes, changes in animal movement, etc.

Development of tick presence mapping simulation tools according to the agricultural landscape

^{© Inra}

Based on the analysis of landscape-scale variations in tick abundance, host abundance and prevalence of three pathogens, the OSCAR project has developed several tools :

• A statistical model to estimate the number of ticks seeking hosts based on different variables describing the landscape and weather conditions.
• Software using this model to represent, from an existing landscape, and under user-selected weather conditions, a mapping of estimated host tick abundance over the three habitat types studied.

A second software is being developed to generate landscapes on which tick abundance mapping (1st software) would be added. The evolution of the density of infected ticks according to different scenarios of land use change and landscape structure would thus be simulated. This virtual landscape could also be used to study, for example, the impact of the decrease in forest area or the relative increase in grassland crops on the risk of tick infection transmission.

With these models, the OSCAR project is paving the way for new knowledge for the adaptation of agriculture to global changes in order to limit the development of tick diseases.

To know more about it

• The leaflet presenting the tools for simulating the abundance of ticks Ixodes ricinus
• Agricultural Landscape and Emerging Zoonotic Diseases Brochure
• ANR OSCAR Program 

Scientific contacts :

Hélène Verheyden
Deputy Director CEFS, 
Inra Occitanie-Toulouse Centre

Olivier Plantard
OSCAR Project Coordinator
UMR INRA - ONIRIS " BIOEPAR "
INRA Centre Pays de la Loire

Gwenaël Vourc'h
Director of UMR EPIA,

Centre Inra Auvergne-Rhône Alps

• Santé animale
• Écologie des Forêts, Prairies et milieux Aquatiques

Associated INRA centres:

• Occitanie-Toulouse
• Auvergne-Rhône-Alpes
• Pays de la Loire