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Context and issues

Tick-borne diseases are the main vector-borne diseases in humans in temperate zones, with I. ricinus species being one of the most widespread and studied vectors. Ixodes ricinus can transmit for example the bacterium Borrelia garinii, one of the agents of Lyme disease in Europe, the main reservoirs of this Borrelia species being birds. Indeed, I. ricinus occasionally feeds on birds. However, other tick species present in France are more specifically associated with birds, such as I. frontalis, which only exceptionally bites humans. Due to the "vector-bridge" role played by the generalist tick I. ricinus, a knowledge of the biology of other tick species that may share the same vertebrate hosts is important in order to better understand the eco-epidemiology of tick-borne diseases and prevent the emergence of new pathogens.

Results

Within the framework of the monthly monitoring of ticks collected on vegetation for the ACCAF CC-EID Metaprogramme projects (2014-2016), then Climatick (2017-2021), focused on the species Ixodes ricinus, unusual densities of larvae were observed from the first autumn of the monitoring, in October and November 2014 in the site studied near Nantes. After morphological identification, these larvae turned out to belong to the species I. frontalis, which had previously been known almost exclusively from collections on birds (thrushes, blackbirds, turtle doves, etc.). The presence of these larvae in large numbers in late autumn and winter has been confirmed every year at this site since monitoring began. This winter peak constitutes an originality compared to the cycle of most European tick species.

In addition, among the 13 transects sampled in this site, I. frontalis was mainly observed in bamboo areas. In order to confirm the link between the presence of this species and a bamboo habitat, 33 sites with this type of vegetation were sampled in winter on a large scale, in metropolitan France and in Italy (1 site). The I. frontalis tick, in all three stages (larva, nymph and adult), was found at 31 of the 33 bamboo sites, confirming the link observed at the site near Nantes.

Among the hypotheses that explain the high presence of the I. frontalis tick on the vegetation under the bamboos is the role of dormitory and protection for the birds played by these groves, which are relatively inaccessible to predators.

Perspectives

This work has enabled us to set up a new study in collaboration with two other laboratories (UMR BIPAR and ASTRE). A study on the microbiota of I. frontalis has been undertaken in order to identify the main symbionts and pathogens associated with this species.

Valorisation

Two publications: 2019 and 2021 (see below)

Bibliographical references

Agoulon, A., Hoch, T., Heylen, D., Chalvet-Monfray, K., Plantard, O. 2019. Unraveling the phenology of Ixodes frontalis, a common but understudied tick species in Europe. Ticks and Tick-Borne Diseases. 10:505-512. https://doi.org/10.1016/j.ttbdis.2018.12.009.

Plantard O., Hoch T., Daveu, R., Rispe, C., Stachurski, F., Boué, F., Poux, V., Cebe, N., Verheyden, H., René-Martellet, M., Chalvet-Monfray, K., Cafiso, A., Olivieri, E., Moutailler, S., Pollet, T., and Agoulon, A. 2021. Where to find questing Ixodes frontalis ticks? Under bamboo bushes! Ticks and Tick-borne Diseases, 12(2):101625. DOI: 10.1016/j.ttbdis.2020.101625.

Female gorged of Ixodes frontalis tick (ventral side) collected from collared dove (26/09/2018).