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A Case of Aseptic Meningitis Caused by Leptospirosis in Gunma Prefecture, Japan

Taketomo Maruki1, Momoko Mawatari1, Nobuo Koizumi2

  • 1Department of Infectious Diseases, Japanese Red Cross Medical Center, Japan.

Internal Medicine (Tokyo, Japan)
|June 17, 2026
PubMed

Insights

A case of rat-associated leptospiral meningitis was diagnosed using cerebrospinal fluid PCR. This highlights leptospirosis as an emerging cause of meningitis in Japan, emphasizing early diagnosis through PCR testing.

Area of Science:

  • Infectious Diseases
  • Neurology
  • Microbiology

Background:

  • Leptospirosis is an emerging infectious disease in Japan, with cases increasing since 2020.
  • Aseptic meningitis is a common diagnosis, but leptospiral meningitis can be an underrecognized cause.
  • Exposure to rodents, such as rat carcasses, is a known risk factor for leptospirosis.

Purpose of the Study:

  • To report a case of leptospiral meningitis in Japan.
  • To highlight the importance of considering leptospirosis in aseptic meningitis cases.
  • To emphasize the utility of cerebrospinal fluid PCR for early diagnosis.

Main Methods:

  • A 50-year-old man presented with symptoms suggestive of meningitis.
  • Cerebrospinal fluid (CSF) analysis, including PCR, was performed.
  • The patient was treated with intravenous ceftriaxone.

Main Results:

  • Leptospira interrogans was identified in the CSF via PCR, confirming leptospiral meningitis.
  • The patient recovered fully after 7 days of antibiotic treatment.
  • 53 cases of leptospirosis were reported in Japan in 2024, indicating an upward trend.

Conclusions:

  • Leptospiral meningitis should be considered in the differential diagnosis of aseptic meningitis, especially in endemic areas.
  • CSF PCR is a valuable tool for the rapid and accurate diagnosis of leptospirosis.
  • Clinicians need to be aware of the evolving epidemiology of leptospirosis in Japan.
Keywords:
Jarisch-Herxheimer reactionLeptospiral meningitisZoonotic disease

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