Spatio-Temporal Diagnostics Reveal Early Signals of Sand Fly Range Shift in Europe

Climate change is reshaping the distribution of vector-borne disease risk in Europe by altering the environmental suitability and phenology of disease vectors such as phlebotomine sand flies, which transmit leishmaniasis. Despite regional observational evidence of sand fly range expansion from Mediterranean areas toward more temperate latitudes, quantitative multi-year diagnostics of such shifts remain limited. Building on the Sand Flies Extreme Prediction Population (FEPO) model, which provides high-resolution daily predictions of sand fly densities across Europe, we introduce a suite of spatio-temporal diagnostics to quantify distributional shifts in density predictions.

We applied these diagnostics to FEPO output for 2021 and 2022 across four Phlebotomus species (P. papatasi, P. perniciosus, P. sergenti, and P. tobbi), using a threshold-based occupancy metric, a density-weighted centroid, and the 95th-percentile front latitude as indicators of spatial redistribution. Using mid-month sampling (one day per month) to balance computational efficiency with seasonal coverage, we detect consistent northward shifts between the two years. Centroid latitude increased by approximately 0.09–0.39° (about 11–44 km) across species, while the 95th-percentile front latitude advanced by approximately 0.17–0.49° (about 19–54 km). The occupied area exceeding a density threshold of 0.1 (model units) increased for all species (0.4–4.5%), with the largest expansion observed for P. perniciosus. Monthly diagnostics further indicate that these shifts are seasonally modulated, with the strongest front differences occurring in the cool season and early spring. As an illustrative example, for P. papatasi, the centroid shifted north by approximately 0.21° (about 23 km) and the front advanced by approximately 0.49° (about 54 km), accompanied by an approximately 2.5% increase in occupied area.

These preliminary two-year diagnostics demonstrate an emergent northward redistribution of predicted sand fly densities in FEPO projections, consistent with broader climatic pressures on vector ecology. While limited in temporal span, the observed shifts highlight the potential of spatio-temporal diagnostics to reveal directional trends in vector population forecasts and to inform public health preparedness.

 

Acknowledgement: The CLIMOS consortium is co-funded by the European Commission grant 101057690 and UKRI grants 10038150 and 10039289. CLIMOS is one of the six Horizon Europe projects, BlueAdapt, CATALYSE, CLIMOS, HIGH Horizons, IDAlert, and TRIGGER, forming the Climate Change and Health Cluster. We also thank the EDENext and VectorNet initiatives, as well as the regional data providers and individual contributors, for their essential datasets.