References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
Treponema pallidum is the spiral-shaped (spirochaete) bacterium that causes syphilis. It’s a fragile organism that can’t survive long outside the human body, which is why syphilis requires direct person-to-person contact for transmission. Understanding the biology helps explain how syphilis is transmitted, diagnosed and treated.
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Key Facts
| Feature | Detail |
|---|---|
| Type | Spirochaete bacterium |
| Shape | Spiral/corkscrew |
| Survival outside body | Very brief — minutes to hours |
| Transmission | Direct contact with syphilitic sore |
| Disease caused | Syphilis (all stages) |
| Treatment | Penicillin (highly effective) |
How It Causes Disease
- Enters through mucous membranes or broken skin
- Causes a painless chancre at the entry site
- Spreads through the bloodstream to all organs
- Can cross the placenta, causing congenital syphilis
- Can invade the nervous system at any stage
Why Syphilis Progresses
T. pallidum evades the immune system by changing its outer surface proteins. This allows it to persist in the body for years or decades if untreated, causing progressive damage through inflammation.
Detection
- Blood tests for antibodies (treponemal and non-treponemal)
- Direct visualisation with dark-field microscopy
- PCR from active lesions
Treatment
Penicillin remains the treatment of choice. T. pallidum has not developed resistance to penicillin despite decades of use — an unusual and fortunate situation.
Why It Matters
- Syphilis rates are rising in the UK
- Early treatment is curative
- Late treatment can prevent but not reverse damage
- Congenital syphilis is preventable with antenatal screening
Read more: What is syphilis? | 4 stages of syphilis | Identifying syphilis sores
Frequently Asked Questions
Can T. pallidum survive on surfaces?
No — it dies quickly outside the body.
Is syphilis still treatable with penicillin?
Yes — penicillin remains highly effective.
Can T. pallidum cause brain damage?
Yes — neurosyphilis can affect the brain if untreated.
Related reading
- The 4 Stages of Syphilis Explained
- Blood Test for Syphilis, Hepatitis B and Hepatitis C
- Can You Catch Syphilis Without Having Sex?
- Cold Sores vs Syphilis Sores: How to Tell the Difference
- How to Identify Syphilis Sores (Chancres)
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
