Syphilis: causes, stages, diagnosis, treatment and prevention

Cause and transmission

The bacterium invades mucous membranes or breaks in the skin and spreads locally and through the bloodstream. Typical routes of transmission include direct contact with an infectious lesion during sexual activity and vertical transmission before or during delivery. Syphilis is not usually spread by casual contact. Awareness of early lesions and routine screening reduce the risk of onward transmission.

Stages and characteristic signs

Syphilis is classically described in four stages with different clinical features and infectiousness. Early recognition at any stage improves outcomes.

• Primary syphilis: A solitary, painless ulcer or wound on the genitals, mouth or other contact site, often on the skin. The lesion, called a chancre, may go unnoticed.
• Secondary syphilis: Systemic spread causes a widespread rash and mucous membrane lesions; other symptoms can include fever, lymph node enlargement and malaise. Classic skin findings may involve the palms and soles.
• Latent syphilis: A period with few or no symptoms despite persistent infection; early latent cases are still infectious, late latent usually are not.
• Tertiary syphilis: Occurs years after initial infection in untreated people and can produce severe, often irreversible damage. Common targets include the nervous system (including the brain and nerves) and the cardiovascular system (notably the heart and large blood vessels).

Diagnosis and treatment

Diagnosis most often uses serologic blood testing to detect antibodies and stage the infection; in some settings the organism can be visualized directly by microscopy or special tests from lesion material. See screening and diagnostic guidance at serologic testing resources and methods for direct detection at microscopy and treponemal tests. Syphilis is treatable: penicillin and other antibiotics remain the mainstay of therapy. Prompt appropriate treatment typically cures the infection and prevents progression, although some late damage may be irreversible.

History, epidemiology and public-health notes

The availability of penicillin in the mid-20th century dramatically reduced the burden of disease in many countries, but syphilis persists worldwide and has shown resurgences in some regions since 2000. Historically and today most cases occur in adults of reproductive age; congenital syphilis is a preventable but still serious global problem. The highest burdens have often been reported in low-resource settings and are described in global surveillance summaries and regional public-health reports (developing-world data).

Complications, interactions and prevention

Untreated syphilis can lead to life-threatening outcomes. Advanced disease may cause neurologic and cardiovascular complications and can be fatal without care. Syphilis infection also increases susceptibility to other sexually transmitted infections, including the risk of acquiring or transmitting HIV. Prevention relies on safer-sex practices, routine screening of sexually active people and prenatal testing to prevent congenital cases. Access to timely medical treatment, partner notification and public-health follow-up remain central to control efforts.

For more clinical, laboratory and patient information consult authoritative sources on diagnosis, management and surveillance: treatments and clinical guidelines are summarized in expert resources (antibiotic therapy), diagnostic algorithms and testing references (blood tests, direct detection), and educational materials for affected families and clinicians (signs and symptoms overview). Additional clinical topics include counseling about congenital infection and pregnancy care (pregnancy guidance), counselling around transmission risks and lesion care (skin and lesion care), and neurologic and cardiac follow-up for advanced disease (neurosyphilis, cardiovascular syphilis).

Research into improved diagnostics, vaccines and public-health strategies continues. Concern remains where screening and treatment access are limited, underscoring the importance of integrating syphilis control into broader sexual and reproductive health services (clinical follow-up, delivery care, fetal monitoring). Community education, routine testing and rapid treatment are the most effective tools available to reduce illness and prevent transmission.