Tick-borne pathogens in ticks collected from Humans: A prospective clinical pilot study

Tick-borne diseases (TBDs), particularly Japanese spotted fever, are an increasing public health concern in Japan. Data on pathogens carried by ticks removed directly from patients and their associated clinical outcomes remain limited. This prospective study investigated pathogen carriage in patient-derived ticks and evaluated the clinical risk of TBDs. Between April and October 2025, ticks were collected from patients presenting with tick bites at two medical institutions in Western Japan. Ticks were morphologically identified and spotted fever group rickettsiae (SFGR) was detected by nested PCR targeting the 17-kDa antigen gene, followed by sequence analysis. Clinical data, including patient background, antibiotic prescriptions, and outcomes, were reviewed. Clinical information was available for 70 patients (median age; 75 years), of whom 88.6% were prescribed prophylactic antibiotics. Ticks were collected from 60 patients (85.7%), and seven adults without antibiotic prophylaxis were followed for disease onset. Sixty-two ticks, predominantly Amblyomma testudinarium (88.7%), were analyzed. SFGR was detected in eight ticks (12.9%), including seven A. testudinarium and one Ixodes nipponensis, collected from seven patients. Two patients bitten by Rickettsia tamurae-carrying ticks were observed for one month without antibiotics and remained asymptomatic. In this prospective analysis, no clinically apparent rickettsiosis was observed following bites from R. tamurae-positive ticks without antibiotic prophylaxis; however, subclinical infection could not be excluded. Despite the small sample size, our findings suggest that the clinical risk associated with R. tamurae infection may be low. Direct analysis of removed ticks from patients may help characterize pathogen reservoirs and inform targeted approaches to TBDs.