The spiral bacterium behind syphilis, an infection that moves through stages and can go quiet for years. Explore its illustrative 3D model, human context, and sources.
PHAC describes T. pallidum as a spiral-shaped, microaerobic, non-spore-forming, motile bacterium measuring 6 to 20 micrometres in length and 0.1 to 0.2 micrometres in diameter, with a protoplasmic cylinder and cytoplasmic membrane bound by a thin peptidoglycan sacculus and outer membrane; although structurally double-membraned, its outer membrane lacks lipopolysaccharides and differs markedly from a typical Gram-negative outer membrane. It could not be grown in pure culture for more than a century, and a long-term tissue-culture system was only reported in 2018. WHO estimated 7.1 million new syphilis infections worldwide in 2020, and 1.1 million pregnant women estimated infected in 2022, resulting in over 390,000 adverse birth outcomes. This profile describes the subspecies pallidum, which causes venereal syphilis.
Syphilis alternates between visible stages and latent periods in which, as CDC puts it, there are no visible signs or symptoms. PHAC reports that roughly 15 to 40% of untreated people develop tertiary disease with mortality of 8 to 58% if untreated, and gives an overall transplacental transmission risk of 60 to 80%. Those are population figures for untreated infection; they do not describe a treated person or predict any individual outcome.
Treponema pallidum · A very slender, regularly coiled spirochete. Motility structures remain beneath the outer membrane and are not drawn as external hairs. 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: Treponema pallidum · pathogen safety data sheet.
Source check: 2026-09-20. Educational content; independent scientific review remains pending.