syphilis

Syphilis is a sexually transmitted infection caused by the spirochete Treponema pallidum. It is transmitted mainly through sexual contact, including vaginal, anal, and oral sex, and can be passed from an infected pregnant person to the fetus (congenital syphilis). Blood transfusion is a rare route in settings with screening.

In untreated individuals, the infection progresses through stages: primary syphilis, with a painless chancre at the site of infection; secondary syphilis, featuring rash on the hands and feet, mucous membrane lesions, fever, and lymphadenopathy; and latent syphilis, where no symptoms are present.

Tertiary syphilis can occur years after initial infection and may involve the heart, blood vessels, and nervous system. Neurosyphilis can appear at any stage and may cause headache, vision or hearing problems, or psychiatric symptoms. Congenital syphilis can result in severe fetal and neonatal complications.

Diagnosis relies on serologic testing. Non-treponemal tests such as RPR or VDRL are useful for screening and monitoring treatment response; treponemal tests (FTA-ABS, TP-PA) confirm exposure. Direct detection by dark-field microscopy is possible for active lesions, though less common. Additional testing may assess for neurosyphilis if symptoms or risk factors are present.

Treatment is with antibiotics, most commonly intramuscular benzathine penicillin G. For early syphilis (primary, secondary, or early latent), a single dose of 2.4 million units IM is typical. For late latent or tertiary syphilis, 2.4 million units IM weekly for 3 weeks is used. Neurosyphilis requires intravenous aqueous penicillin G 18–24 million units per day, given as 3–4 million units every 4 hours for 10–14 days. Alternatives include doxycycline for nonpregnant patients; penicillin desensitization is advised for pregnant individuals with penicillin allergy.

Prevention includes safe sex practices, condom use, routine screening in pregnancy, and partner notification. Treatment generally leads to clinical improvement and serologic response, though titers may decline slowly and require follow-up testing over 6 to 24 months.