- Caused by spirochete Treponema pallidum

Primary syphilis: Painless chancre. VDRL ⊕ in 80%, dark-field microscopy.

Secondary syphilis: Maculopapular rash (including palms and soles), condylomata lata (smooth, moist, painless, wart-like white lesions on genitals), lymphadenopathy, patchy hair loss. Serologic testing: VDRL/RPR (nonspecific), confirm diagnosis with specific test (FTA-ABS).

Latent syphilis (⊕ serology without symptoms) may follow.

Tertiary syphilis: Gummas (chronic granulomas), aortitis (vasa vasorum destruction), neurosyphilis (tabes dorsalis), Argyll Robertson pupil (constricts with accommodation but is not reactive to light; also called "prostitute's pupil"). Signs: broad-based ataxia, ⊕ Romberg, Charcot joint, stroke without hypertension.

Congenital syphilis: Facial abnormalitis with rhagades (linear scars at angle of mouth), snuffles (nasal discharge), saddle nose, notched (Hutchinson) teeth, mulberry molars, and short maxilla; saber shins; CN VIII deafness. Placental transmission typically occurs after first trimester.