Spatial disaggregation of tick occurrence and ecology at a local scale as a preliminary step for spatial surveillance of tick-borne diseases : general framework and health implications in Belgium

Abstract

BACKGROUND: The incidence of tick-borne diseases is increasing in Europe. Sub national information on tick distribution, ecology and vector status is often lacking. However, precise location of infection risk can lead to better targeted prevention measures, surveillance and control. METHODS: In this context, the current paper compiled geolocated tick occurrences in Belgium, a country where tick-borne disease has received little attention, in order to highlight the potential value of spatial approaches and draw some recommendations for future research priorities. RESULTS: Mapping of 89,289 ticks over 654 sites revealed that ticks such as Ixodes ricinus and Ixodes hexagonus are largely present while Dermacentor reticulatus has a patchy distribution. Suspected hot spots of tick diversity might favor pathogen exchanges and suspected hot spots of I. ricinus abundance might increase human-vector contact locally. This underlines the necessity to map pathogens and ticks in detail. While I. ricinus is the main vector, I. hexagonus is a vector and reservoir of Borrelia burgdorferi s.l., which is active the whole year and is also found in urban settings. This and other nidiculous species bite humans less frequently, but seem to harbour pathogens. Their role in maintaining a pathogenic cycle within the wildlife merits investigation as they might facilitate transmission to humans if co-occurring with I. ricinus. Many micro-organisms are found abroad in tick species present in Belgium. Most have not been recorded locally but have not been searched for. Some are transmitted directly at the time of the bite, suggesting promotion of tick avoidance additionally to tick removal. CONCLUSION: This countrywide approach to tick-borne diseases has helped delineate recommendations for future research priorities necessary to design public health policies aimed at spatially integrating the major components of the ecological cycle of tick-borne diseases. A systematic survey of tick species and associated pathogens is called for in Europe, as well as better characterisation of species interaction in the ecology of tick-borne diseases, those being all tick species, pathogens, hosts and other species which might play a role in tick-borne diseases complex ecosystems.