Leech as potential vectors in Japanese Spotted Fever and their epidemiological study

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K23972
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0902:General internal medicine and related fields
• Research Institution: Fukushima Medical University (2021-2022); Nagasaki University (2019-2020)
• Principal Investigator: Sando Eiichiro 福島県立医科大学, 医学部, 教授 (30849542)
• Project Period (FY): 2019-08-30 – 2023-03-31
• Keywords: 発疹熱 / 日本紅斑熱 / つつが虫病 / リケッチア感染症 / ヤマビル / ダニ / ベクター媒介感染症

Outline of Final Research Achievements

We were unable to detect Rickettsia japonica DNA, the causative pathogen of Japanese spotted fever, in 175 leech specimens. However, we obtained novel seroepidemiological findings. Rickettsial infections in southern Chiba Prefecture, which were previously thought to be caused by tsutsugamushi disease and Japanese spotted fever, were found to have the highest antibody positivity rate for Rickettsia typhi, the pathogen causing murine typhus. Furthermore, we investigated the serological cross-reactivity between R. japonica and R. typhi. Both IgM and IgG cross-reactivity were observed at a frequency of approximately 20%. Moreover, by comparing antibody titers during the acute and convalescent phases, we were able to differentiate between the two diseases in most cases showing cross-reactivity.

Free Research Field

臨床感染症

Academic Significance and Societal Importance of the Research Achievements

リケッチア感染症の一つである発疹熱は、元々風土病として知られていたが、リケッチア感染症の報告は第4類感染症のつつが虫病や日本紅斑熱がほとんどで、届出義務のない発疹熱の国内事例はほとんど報告がなかった。今回、リケッチア感染症の流行地域で研究を行い、血清疫学的につつが虫病や日本紅斑熱よりも、発疹熱（Rickettsia typhi）の抗体陽性率が最も高く、同時に日本紅斑熱患者における交差反応はあっても限定的であることも明らかにした。つまり、ほとんどの発疹熱患者が診断されていなかったことを示唆している。そのため、発疹熱の診断と報告体制の構築が、実態把握のために喫緊の課題であることを示した。