Explore the recorded discovery and history of Leptospira interrogans, with source links and stated limits.
Bilung and colleagues describe Leptospira as finely coiled, filamentous spirochetes, extremely thin and helically coiled, typically measuring 6 to 20 micrometres in length and approximately 0.1 micrometre in diameter, with question-mark hook-shaped ends that distinguish them from other spirochetes, a double-membrane envelope and periplasmic endoflagella anchored at both cell poles. They stain poorly with conventional dyes including Gram stain and are too thin to be seen by ordinary light microscopy, so dark-field or phase-contrast microscopy is used. PHAC records at least 218 serovars in 23 serogroups. CDC states that about 1 million cases occur globally each year with nearly 60,000 deaths, and that the bacteria are spread through the urine of infected animals and can survive in contaminated water or soil for weeks to months.
LPSN records the basonym “Spirochaeta interrogans” Stimson 1907, with the etymology noting that interrogans means asking or interrogating, here meaning shaped like a question mark. The 2026 review adds that Arthur Stimson made the first microscopic identification of the spirochete in 1907 and named it for the hook at the end resembling a question mark.
The 2026 review records that the microorganism was isolated by Inada and colleagues in Japan in 1915, who found specific antibodies in the blood of miners who had contracted the illness. Isolation from patients is a separate milestone from first microscopic observation.
LPSN records Leptospira interrogans (Stimson 1907) Wenyon 1926, retained on the 1980 Approved Lists of Bacterial Names. Type strain serogroup Icterohaemorrhagiae, serovar Icterohaemorrhagiae, strain RGA / ATCC 43642 / DSM 21525.
These references do not identify a first person ever infected. The 1907 observation and 1915 isolation record laboratory milestones in the United States and Japan respectively, in patients who were already ill, so neither dates a first human case or establishes where the organism arose.
Source check: 2026-09-20. Educational content; independent scientific review remains pending.