Primary Syphilis

Primary syphilis is the first stage of infection by Treponema pallidum, presenting as a painless ulcer (chancre) at the site of inoculation 10 to 90 days (average 3 weeks) after exposure. It is transmitted by sexual contact, including oral and anal sex, and across the placenta.

• Highly infectious when the chancre is present.
• HIV infection and other genital ulcers increase transmission in both directions.

Solitary, painless, indurated ulcer with a clean base and raised edges on the genitals, anus, rectum, lips or oral cavity, with firm painless regional lymphadenopathy.

• Chancres may be multiple, atypical or painful (especially in HIV), or unnoticed (cervix, anus, mouth).
• Heals spontaneously in 3 to 6 weeks, leaving a sign of infection only in blood tests.
• Differential diagnosis: genital herpes, chancroid, lymphogranuloma venereum, donovanosis, trauma, fixed drug eruption, Behcet disease, squamous cell carcinoma, scabies, aphthous ulcer, mpox.
• Complications: progression to secondary, latent and tertiary syphilis, congenital syphilis, secondary bacterial infection, neurosyphilis, increased HIV acquisition.

Direct detection plus serology.

• Dark field microscopy or PCR of ulcer exudate; direct fluorescent antibody.
• Serology: treponemal tests (TPHA, TPPA, EIA, rapid test) and non treponemal tests (RPR or VDRL); serology may be negative in the first 2 to 4 weeks, so repeat after 2 to 4 weeks if suspicion is high.
• HIV test, hepatitis B and C, gonorrhoea and chlamydia NAAT, pregnancy test.
• CSF examination and eye review if neurological or visual symptoms.

Single dose penicillin is curative.

• Supportive: counselling, no sex until the ulcer heals and 7 days after treatment, notify and treat partners from the previous 90 days, condoms, HIV and STI screening, hepatitis B vaccination, warn about the Jarisch Herxheimer reaction.
• Pharmacological: benzathine benzylpenicillin 2.4 million units IM single dose (children 50,000 units/kg, maximum 2.4 million units). Penicillin allergy (not pregnant): doxycycline 100 mg twice daily for 14 days; alternatively ceftriaxone 1 g IM or IV daily for 10 days. Jarisch Herxheimer reaction: paracetamol 1 g and fluids.
• Procedures: none; lumbar puncture for neurological or ocular signs.
• Special groups: pregnancy, penicillin only (desensitise if allergic), with a second dose after 1 week in the third trimester; HIV, give benzathine benzylpenicillin 2.4 million units IM with closer serological follow up; children, evaluate for congenital syphilis and abuse; penicillin allergy, skin testing and desensitisation.
• Red flags: neurological or visual symptoms, hearing loss, pregnancy, treatment failure with a rising titre, multiple or large ulcers in HIV.
• Follow-up: RPR or VDRL titre at baseline and at 3, 6 and 12 months (also 24 months in HIV); a fourfold fall by 6 to 12 months shows cure; a fourfold rise needs retreatment and CSF examination.