Predicting the distribution of 16 tick species in Japan and its association with the occurrence of tick-borne diseases

Abstract

Tick-borne diseases are a significant public health threat. Since the infection risk is directly associated with spatial variations of vector ticks, comprehensive data on their distributions are crucial for disease preparedness. Nevertheless, the difficulty of conducting field surveys over large geographical regions often restricts tick distribution data to localized areas. To overcome this limitation, we combined a nationwide tick survey and species distribution modeling to comprehensively map the potential distribution of ticks in the Japanese archipelago. Ticks were collected by the flagging method at 1,018 sites across 38 prefectures in Japan from 2013 to 2025. The potential suitable habitats of each species were predicted at a 1 km resolution by the maximum entropy method, using climatic, topographic, and landscape variables. The predicted probabilities were converted to proportions of predicted presence grids at the prefectural level and used in regression analyses to examine whether the distribution of each tick species can explain the occurrence of five notifiable tick-borne diseases in Japan. A total of 22,416 ticks were collected, and the distributions of 16 tick species were predicted across Japan with robust model performance. The predicted suitable habitats exhibited diverse interspecific variations, including both latitudinal and elevational gradients. Among the variables considered, snow depth was identified as a fundamental determinant of tick distributions, yielding the highest percentage contribution for six species. The regression analyses demonstrated significant correlations between the predicted area occupancy of suspected vector tick species and the reported number of each tick-borne disease. Notably, the distributions of Ixodes pavlovskyi and Ixodes persulcatus aligned closely with the occurrence of diseases with a northern distribution such as Lyme disease. In contrast, Haemaphysalis flava was the primary and secondary contributor to model performance for the diseases with a southern distribution (Japanese spotted fever and severe fever with thrombocytopenia syndrome, respectively). These correlated species are known vectors of their corresponding diseases. This study established the first comprehensive distribution models for 16 tick species in Japan. The maps provided by this study, offering a nationwide overview of tick distributions, serve as basic information for anticipating the occurrence of tick-borne diseases in this region.