A hook-ended spirochete spread through animal urine in water and soil, causing everything from a flu-like week to organ failure. Explore its illustrative 3D model, human context, and sources.
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.
PHAC describes a low case fatality rate that increases with age, an illness lasting 3 days to a few weeks, and a biphasic pattern. Severe disease — Weil’s disease with jaundice, renal insufficiency, anaemia and haemorrhage — is a minority outcome. CDC notes that many symptoms resemble other illnesses and that some infected people show no signs at all, so both over- and under-diagnosis are plausible.
Leptospira interrogans · A very fine, closely coiled spirochete with a hooked terminus. Its motility structures stay below the outer membrane. This is a species-informed teaching diagram; colours, proportions, envelope spacing and internal detail are illustrative. The model uses muted illustrative colours; stains, colony pigments and microscopy colourization are not natural cell colours. Anatomy is enlarged for phone viewing. Morphology reference: Leptospira and leptospirosis: a review of species classifications, genomes, morphological structures, transmissions and clinical manifestations.
Source check: 2026-09-20. Educational content; independent scientific review remains pending.