Climate change impacts on the global potential distribution of the human flea, Pulex irritans, and the global health risks

The human flea, Pulex irritans, is a hematophagous ectoparasite and medically significant vector of zoonotic pathogens, such as Yersinia pestis (plague), Bartonella quintana (trench fever), and Rickettsia felis (flea-borne spotted fever). Despite the public health significance of P. irritans, the potential impacts of climate change on its global distribution were unstudied before. In this study, we created an ecological niche model (ENM) through integrating 564 georeferenced records and 15 bioclimatic variables using the Maximum Entropy (MaxEnt) algorithm to project the current and future habitat suitability of P. irritans under two high-emission scenarios (SSP370 and SSP585) for 2050 and 2070 from three General Circulation Models (GCMs). DIVA- GIS was used to confirm the current predictions. Results revealed that the Model’s performance was robust with high predictive accuracy (AUC = 0.898; TSS = 0.6), identifying annual mean temperature (Bio1) with 55.9% contribution as the primary distribution variable. The models project that many species across North and South America, Europe, Asia, Australia, and Africa will expand their ranges toward higher latitudes. Regions once deemed unsuitable, including northern Europe, Canada, and Russia, are forecast to become suitable habitats as these species shift their geographical distribution. On the other hand, habitat loss was predicted in Africa and Australia due to extreme warming. Two-dimensional niche analysis revealed the broad tolerances of P. irritans (2–25 °C; 0–2200 mm), confirming its invasive potential. These shifts correlate with increased plague risk in temperate zones, as warmer temperatures accelerate flea life cycles and pathogen transmission efficiency. Our findings provide the first global assessment of climate-driven redistribution of P. irritans, highlighting the urgent need for surveillance in vulnerable regions to mitigate emerging vector-borne disease threats.