Epidemiological and molecular characteristics of human-biting ticks in areas endemic to Japanese spotted fever: a prospective study

Tick-borne diseases (TBDs) have become a great health concern worldwide. This study aimed to clarify the pathogenic and potentially pathogenic microorganisms carried by ticks that bite humans and to assess the risk of acquiring tick-borne infections in regions endemic for Japanese spotted fever. Tick specimens were prospectively collected from patients who presented with tick bites at 10 medical institutions in the Hiroshima, Okayama, and Kagawa prefectures, Japan between May 2023 and December 2024. The evaluated parameters included the estimated bite location, date of bite, patient age, tick species identification, and presence of TBD-associated pathogens in the collected ticks. Overall, 191 ticks were collected from 181 patients. Among patients with known sex, females were slightly more prevalent than males, and 45.9% of the patients were aged ≥ 70 years. Seasonal distribution demonstrated a peak incidence from April to July, with the highest number of cases observed in June (29.3%). Amblyomma testudinarium was the predominant species, accounting for 152 (79.6%) ticks, followed by Haemaphysalis hystricis (7.3%) and Haemaphysalis longicornis (6.8%). Nymphs represented the majority (83.8%), whereas adults and larvae accounted for 14.6% and 1.0%, respectively. A total of 27 ticks (14.1%) carried Rickettsia species, including two identified species (Rickettsia tamurae and Rickettsia monacensis) and one unclassified Rickettsia species. However, molecular analysis did not detect any known human pathogenic organisms, including Ehrlichia and Anaplasma species, Francisella tularensis, or Rickettsia japonica. Further epidemiological data regarding the abundance of tick-borne pathogens will provide valuable surveillance information with significant clinical utility for disease diagnosis and management.