Japanese Society for Infection Prevention and Control-Online Journal

Full Text of PDF (381K)
Article in Japanese

Changing Landscape of Tick-Borne Infections in Japan

Hiromichi IWASAKI
Tannan Health and Welfare Center

In recent years, several novel tick-borne viral infections have been identified in Japan, including tick-borne encephalitis (TBE), Yezo virus infection, and Oz virus infection. Although the number of reported domestic cases remains limited, the potential for future outbreaks is a growing concern due to the likely expansion of vector tick habitat, driven by global warming and shifts in the distribution of wild animals hosts. In addition, a new serotype (Shimokoshi type) of Orientia tsutsugamushi has been identified in scrub typhus, a rickettsial disease transmitted by chigger mites, which are significantly smaller than ticks.
The primary tick-borne diseases endemic to Japan include scrub typhus, Japanese spotted fever (JSF), and severe fever with thrombocytopenia syndrome (SFTS). Notably, the incidence of JSF and SFTS has increased markedly in recent years. Scrub typhus and JSF are both caused by Rickettsia species and respond well to tetracyclines. In contrast, SFTS is a viral infection for which favipiravir was approved as a treatment option in 2024. Clinically, scrub typhus and JSF share a classic triad of symptom: fever, rash, and eschar, often complicating differential Diagnosis. However, scrub typhus typically demonstrates rapid improvement following tetracyclines therapy, whereas JSF tends to have more protracted recovery period and a higher risk for severe complications, potentially related to cytokine storm. SFTS usually presents with fever but often lacks the characteristic rash or eschar. Furthermore, minimal elevation of C-reactive protein (CRP) levels in laboratory findings may aid in distinguishing SFTS from rickettsial infections.

Key words：scrub typhus, Japanese spotted fever, sever fever with thrombocytopenia syndrome: SFTS, Yezo virus: YEZV, Oz virus: OZV

e-mail: hiwasaki＠u-fukui.ac.jp

Received: April 24, 2025
Accepted: May 19, 2025

40 (4)：159─163,2025