Global risk assessment of Lyme borreliosis transmission

We analyzed the geographic risk of Lyme borreliosis taking into account the biogeography of tick vectors and wild carrier hosts, together with environmental and anthropogenic factors. Four pathogeographical scenarios were set in order to represent the contribution of vectors and hosts in the spatial zoonotic risk. For that propose, we built distribution models based on the occurrence of Lyme borreliosis cases in humans and ixodid vectors. Besides Ixodes species, we considered other ixodid ticks with potential to be vectors. These models were combined through fuzzy logic operators, according to the criteria established in each scenario. Finally, the transmission risk model for Lyme borreliosis which best fitted its global distribution was selected. The risk model selected considered ixodid vectors and mammal carriers as explanatory variables together with environment and anthropogenic factors. Ixodes species contributed to explain the geographical risk of Lyme borreliosis to a larger extent than other ixodid ticks. The risk model described regions with Lyme borreliosis transmission risk where its presence is still uncertain, such as northern Africa and inland areas of western U.S.A. Likewise, our model indicated favorable conditions for the presence of human cases in northern latitudes beyond its endemic distribution. Applying this multi-scenario methodology approach have led us to a risk model, in which the diversity of ixodid vectors and carrier hosts might modify the spatial risk without a geographical limitation.