The infection
Syphilis is caused by the spiral bacterium Treponema pallidum. After decades of decline it is rising sharply again: in Europe, its rate more than doubled between 2015 and 2024 (ECDC, 2026). Its progression through several stages, separated by phases with no symptoms whatsoever, makes it deceptive: many people discover it years after infection, through routine serology or a blood donation.
Key facts
| Organism | Bacterium Treponema pallidum |
|---|---|
| Incubation | 10 to 90 days |
| Stages | Primary (chancre), secondary (rash), latent, tertiary |
| Reliable testing from | Six weeks, with confirmation at three months |
| Test | Serology: a treponemal and a non-treponemal test together |
| Curable | Yes, with penicillin, at every stage |
| Pregnancy | Routine screening: congenital syphilis is severe |
How it is transmitted
It passes through direct contact with an infectious lesion, most often during vaginal, anal or oral sex. Because the chancre is painless and may sit inside the mouth, vagina or anus, it very often goes unnoticed. Condoms reduce but do not remove the risk, since lesions can lie outside the area they cover. Transmission from mother to baby during pregnancy is the most serious form.
Symptoms
The first stage is a chancre: a single, firm, clean-edged and above all painless ulcer that heals on its own within weeks, which falsely reassures. The second stage follows about six to sixteen weeks after infection (ameli, 2025): a rash that characteristically involves the palms and soles, fever, swollen glands, patchy hair loss, and highly infectious mucous lesions. Everything then disappears again, sometimes for years. The late stage can affect the heart, blood vessels, bones and nervous system.
Testing
Diagnosis rests on two complementary blood tests: a treponemal test, which stays positive for life and records contact with the organism, and a non-treponemal test, whose titre reflects disease activity and is used to follow treatment. Antibodies take weeks to appear, so a test done too early can be negative despite a visible chancre. Testing at six weeks and again at three months is needed after exposure.
Treatment
A single intramuscular injection of benzathine penicillin clears early syphilis; late or undated infection requires three weekly injections. Doxycycline is used where there is penicillin allergy. A feverish reaction within hours of the injection, the Jarisch-Herxheimer reaction, is common and harmless: it reflects the mass destruction of bacteria. Serological follow-up over a year is needed to confirm cure.
If left untreated
Untreated, syphilis can after years affect the aorta, bones and nervous system, with neurological and psychiatric consequences. Neurological and ocular involvement can, however, occur at any stage including early disease. In pregnancy it causes late miscarriage, stillbirth and severe malformation — all preventable by a screening test and one injection.
Prevention
- Condoms reduce but do not eliminate risk: lesions may lie outside the covered area.
- Screening is routine in early pregnancy and should be repeated in the third trimester after any exposure.
- Regular testing is advised with multiple partners, since syphilis is so often symptomless.
- Doxycycline taken within 72 hours of sex substantially reduces syphilis risk and is offered to some highly exposed groups.
After a diagnosis
- Notify partners from the last three months for primary syphilis and six months for secondary syphilis, plus the time symptoms have lasted (CDC, 2021), and from the last year for early latent infection.
- Complete the serological follow-up: cure is proved by a falling titre, not by the disappearance of symptoms.
- Add an HIV test: syphilis markedly increases HIV transmission risk.
- Declare any pregnancy: treatment and monitoring are adapted accordingly.
Worth remembering
The syphilis chancre is painless and heals by itself. That is precisely what makes the infection dangerous: its disappearance is not recovery, it marks the move to the next stage.
A little history
The first documented epidemic broke out in Naples in 1494-1495, in the army of Charles VIII of France: the Italians called it the "French disease", the French the "Neapolitan disease", and every nation blamed its neighbour. The name comes from a poem by the physician Girolamo Fracastoro (1530), whose shepherd Syphilus is punished with the illness. Where did it come from? The "Columbian" hypothesis has it brought back from the Americas by Columbus's sailors in 1493 — the epidemic follows their return very closely; the "pre-Columbian" hypothesis sees a disease already present in Europe and confused with leprosy. European skeletons from before 1493 said to bear syphilitic lesions remain disputed, and the debate is not settled.
For four centuries the treatment was mercury — as ointment, fumigation or pills — so toxic that people said "a night with Venus, a lifetime with Mercury", then guaiacum wood imported from the New World. The microbe, Treponema pallidum, was only identified in 1905 by Fritz Schaudinn and Erich Hoffmann in Berlin; the Wassermann blood test followed in 1906; in 1910 Salvarsan, developed by Paul Ehrlich and Sahachiro Hata from arsenic, became the first synthetic drug aimed at a microbe. Penicillin, tested on syphilis by John Mahoney in 1943, finally made the disease curable with a few injections.
The story has its dark side too: from 1932 to 1972 the United States Public Health Service observed, without treating them, nearly 400 Black men with syphilis in Tuskegee, Alabama — even after penicillin arrived; in Guatemala, in 1946-1948, prisoners and patients were deliberately infected. Those scandals founded the modern rules of research ethics. After a historic low around 2000, syphilis has been rising again in most rich countries for some twenty years.
How this differs between countries
The treatment has been the same everywhere for seventy years. What differs is the testing — above all in pregnancy.
- Antenatal screening. Routine and early in most countries, incomplete in others. Congenital syphilis is entirely preventable by one test and one injection, so every case marks a missed opportunity.
- Third-trimester retesting. Recommended where incidence is rising, absent elsewhere.
- Doxycycline prophylaxis. Taking doxycycline within 72 hours of sex is recommended for some highly exposed groups in France, the United States, Canada and Australia; it is not offered in most other countries.
- Penicillin supply. Shortages of benzathine penicillin have affected several countries in recent years, forcing the use of less well-evidenced alternatives.
- Resurgence. Incidence has risen sharply in Europe, where rates more than doubled between 2015 and 2024, after decades of decline.