Comprehensive analysis of the potential risk of tick-borne emerging infectious diseases caused by pathogenic Rickettsiales bacteria

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K07499
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 49050:Bacteriology-related
• Research Institution: University of Shizuoka
• Principal Investigator: Ohashi Norio 静岡県立大学, 食品栄養科学部, 教授 (10169039)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: Rickettsiales / Rickettsia japonica / Japanese spotted fever / Ehrlichia / Tick

Outline of Final Research Achievements

To elucidate the potential risk of tick-borne emerging infectious diseases caused by Rickettsiales bacteria, we analyzed comprehensively pathogenic Rickettsiales bacteria in ticks and blood in febrile patients with Japanese spotted fever by next-generation sequencing and qPCR. As a result, we found that (i) some individual ticks harbor multiple pathogenic Rickettsiales bacteria which may cause the mixed infections in humans, (ii) a candidate of human ehrlichiosis agent in ticks in Japan was successfully indetified, and (iii) the amount of Rickettsia japonica in blood from feburile patients and/or the opportunistic infection by some facultative bacteria may be involved in the risk for severity of Japanese spotted fever. Thus, these results are expected to greatly contribute to the control and treatment of tick-borne infectious diseases caused by pathogenic Rickettsiales bacteria in Japan in the future.

Free Research Field

微生物学

Academic Significance and Societal Importance of the Research Achievements

本研究の学術的意義としては、(i) マダニ1個体において、複数の病原性リケッチア目細菌の混在が明らかになったこと、(ii) 日本国内のマダニには、ヒトに感染性を示すEhrlichia属菌が潜在していること、(iii) 日本紅斑熱の重症化リスクには、血液中のリケッチア量や日和見感染菌との混合感染が係わっている可能性があること、などである。社会的意義としては、公衆衛生学上、啓発活動に役立つ知見が得られたこと、および日本紅斑熱の治療において、重症化を抑えるヒントとなる情報が得られたこと、などである。