syphilis

syphilis
Name	Syphilis
Synonyms	Lues
Caption	Treponema pallidum, the causative bacterium, as seen through a dark-field microscope
Field	Infectious disease
Symptoms	Variable by stage; chancre, rash, fever, neurological and cardiovascular complications
Complications	Neurosyphilis, aortitis, gummata
Onset	3–90 days after exposure
Duration	Lifelong without treatment
Causes	Treponema pallidum subspecies pallidum
Risks	Unprotected sexual contact, mother-to-child transmission
Diagnosis	Blood tests, dark-field microscopy of lesions
Differential	Chancroid, herpes simplex, psoriasis, other rashes
Prevention	Condom use, safe sex practices, penicillin treatment of infected pregnant women
Treatment	Penicillin G (typically benzathine benzylpenicillin)
Prognosis	Excellent with early treatment
Frequency	~7 million new cases worldwide (2020, WHO estimate)

Syphilis is a complex sexually transmitted infection caused by the spirochete bacterium Treponema pallidum. The disease progresses through distinct clinical stages—primary, secondary, latent, and tertiary—and can affect nearly every organ system, including the brain, heart, and aorta. Its history is deeply intertwined with major societal changes, wars, and the development of modern antibiotic therapy, most notably penicillin.

Signs and symptoms

The primary stage classically presents with a single, painless ulcer known as a chancre at the site of inoculation, such as the genitals, anus, or mouth. In the secondary stage, a diffuse, non-itchy rash often involving the palms and soles appears, accompanied by systemic symptoms like fever, sore throat, and lymphadenopathy. The latent stage has no visible symptoms. Tertiary disease, now rare, can manifest decades later with severe complications including destructive gummata, life-threatening cardiovascular syphilis like aortitis, and debilitating neurosyphilis, which can present as general paresis or tabes dorsalis.

Cause and transmission

The causative agent is the spiral-shaped bacterium Treponema pallidum subspecies pallidum. Transmission occurs primarily through direct contact with infectious lesions during vaginal, anal, or oral sex. It can also be transmitted from an infected pregnant person to the fetus, resulting in congenital syphilis, or rarely through blood transfusion. The bacterium is extremely fragile outside the human body, unable to survive on surfaces.

Diagnosis

Diagnosis relies on a combination of clinical assessment and laboratory testing. Direct visualization of the bacterium from exudate of a primary chancre using dark-field microscopy is definitive. Serological testing is the mainstay, beginning with non-treponemal tests like the Rapid Plasma Reagin or Venereal Disease Research Laboratory test, followed by confirmatory treponemal tests such as the Treponema pallidum particle agglutination assay or fluorescent treponemal antibody absorption test. In neurosyphilis, analysis of cerebrospinal fluid is required.

Prevention

Consistent and correct use of latex condoms reduces but does not eliminate transmission risk. Public health strategies include routine prenatal screening of all pregnant individuals and prompt treatment of those infected to prevent congenital syphilis. Partner notification and treatment, or contact tracing, are critical components of sexually transmitted infection control programs led by agencies like the Centers for Disease Control and Prevention and the World Health Organization.

Treatment

The preferred treatment for most stages is a single intramuscular dose of long-acting benzathine benzylpenicillin. For neurosyphilis, a longer course of intravenous penicillin G is required. For patients with a documented penicillin allergy, desensitization followed by penicillin is recommended, as alternatives like doxycycline or ceftriaxone have less robust evidence. The Jarisch-Herxheimer reaction, a transient febrile illness, can occur after initial treatment.

History

The origins of syphilis in the Old World are highly debated, with the predominant Columbian theory suggesting it was brought to Europe after the voyages of Christopher Columbus. Major epidemics, known as the "Great Pox," swept through Europe in the late 15th and 16th centuries. Key historical figures involved in its study include Philippe Ricord, who described its stages, and August von Wassermann, who developed an early serological test. The Tuskegee syphilis experiment remains a profound ethical scandal in medical history.

Epidemiology

According to the World Health Organization, there were an estimated 7 million new cases globally in 2020. Rates have been rising in many high-income nations, including the United States, particularly among men who have sex with men. The resurgence is linked to factors including decreased condom use and increased sexual networking facilitated by dating apps. Congenital syphilis cases have also increased alarmingly in regions like the American South and Sub-Saharan Africa.

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