Patterns of tick infestation and tick-borne pathogen prevalence in sika deer and brown bears in Hokkaido, Japan.

Understanding the interactions among hosts, vectors, and pathogens is essential for elucidating the ecology of tick-borne diseases. However, studies on tick fauna and pathogenic infections in large mammals in Hokkaido, Japan remain limited. We examined the spatial and temporal (region and season) and host factors (sex and age) affecting pathogen prevalence and tick infestation in sika deer (Cervus nippon yesoensis) and brown bears (Ursus arctos yesoensis) in Hokkaido. We selected Anaplasma and Hepatozoon, two prevalent pathogens in sika deer and brown bears, respectively, to analyze host-vector-pathogen relationships. Between 2021 and 2024, we tested samples from 223 deer and 437 bears for these pathogens and examined tick infestation patterns in 157 deer and 255 bears across four regions. Anaplasma infection prevalence was high in deer from South and East Hokkaido but low in those from North Hokkaido. Hepatozoon infection in bears was high in South and Central Hokkaido, and low in the East and North. Generalized linear mixed models (GLMMs) indicated that Anaplasma prevalence was determined by regional factors, whereas Hepatozoon infection was influenced by region and host age, with adults showing lower infection rates. Six tick species were identified: Ixodes ovatus, Ixodes persulcatus, Haemaphysalis japonica, Haemaphysalis megaspinosa, Haemaphysalis flava, and Haemaphysalis longicornis. The GLMMs revealed that I. ovatus was more prevalent on male deer than females. Conversely, I. persulcatus nymphs were less prevalent male bears than females. Older hosts showed higher levels of infestation across multiple tick species. These findings reveal the complex interplay shaping tick-borne disease ecology in wildlife.