What is syphilis?
Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum. The good news is that it is curable, but the medicine and duration depend on the stage and the organs involved, not one injection plan for everyone.[1]
Syphilis has been called “the great imitator” because its symptoms vary and often disappear temporarily, so many people assume they are better while the infection persists.
Why it should not be left untreated
Although treatable, untreated syphilis can spread to the nervous system, eyes, ears or heart, and in pregnancy it can cross the placenta, causing miscarriage, stillbirth or congenital syphilis.[1] Early diagnosis and treatment matter a great deal.
How common is it?
The World Health Organization estimated about eight million new syphilis infections worldwide among people aged 15–49 in 2022.[4] This is global incidence, not the prevalence in any single country, but it shows syphilis remains common and is rising in many places.
The stages of syphilis
Syphilis spreads through contact with infectious sores or rashes during sex, and across the placenta. Symptoms can resolve while infection continues.[1],[2] The stages are:
- Primary: usually a painless, firm sore where the bacteria entered, such as the genitals, anus or mouth. It heals by itself within weeks.
- Secondary: a body rash, often on the palms and soles, possibly with fever, swollen glands or patchy hair loss.
- Latent: no symptoms; found only by blood tests. Divided into early and late latent.
- Tertiary: affecting the nervous system, heart or other organs; now uncommon.
Neurological, ocular and ear involvement can occur at any stage.
Reading syphilis blood tests
Diagnosis uses two types of blood test together.[1],[2]
- Treponemal tests, such as TPHA or TP antibody, show whether you have ever been infected. They usually stay positive for life, even after cure.
- Non-treponemal tests, such as RPR or VDRL, reflect current activity and are used to monitor treatment.
A single reactive test does not prove a new infection. Results must be interpreted with previous treatment history and stage.[1],[2]
Treatment and follow-up
Penicillin is the main treatment, with the formulation and duration chosen by stage. For primary, secondary and early latent syphilis, CDC guidance uses a single intramuscular injection of benzathine penicillin G. Late latent or unknown-duration syphilis needs three weekly injections, and neurological or ocular syphilis needs intravenous treatment.[1],[2]
Tell your doctor if you are pregnant or have a penicillin allergy, because the plan may need to change.[1]
Follow-up blood tests. RPR or VDRL is repeated at intervals to confirm the expected fall. Missing follow-up means not knowing whether treatment worked.[1]
Partner care. Partners should be assessed and treated, and reinfection is possible. A test taken very soon after exposure may be negative and need repeating.[1]
How we care for you at Dr. Kris Clinic
We test for syphilis confidentially, explain what both blood tests mean, and assess the stage before planning treatment, in English or Thai. If treatment is needed, we arrange the injections and follow-up blood tests.
We help plan partner notification appropriately and recommend testing for other STIs, including HIV, which often occur together. If you have eye or neurological symptoms, we refer you urgently for specialist treatment.
Frequently asked questions
My sore healed on its own. Am I cured?
No. The primary sore heals by itself, but the bacteria remain and progress. Blood tests and treatment are needed.
Why is my blood test still positive after treatment?
Treponemal tests usually stay positive for life. Treatment is monitored by a falling RPR or VDRL.
Can I get syphilis again?
Yes. Treatment does not give lasting immunity, so partners need testing and treatment too.
What if I'm allergic to penicillin?
Tell your doctor, who will consider alternatives or an appropriate approach for your stage, especially in pregnancy.
Treat syphilis according to stage, monitor blood tests to confirm response, and arrange partner care at the same time.[1] Eye, ear or neurological symptoms need prompt assessment.
Talk to a doctor about this
Confidential care in Surat Thani, the mainland gateway to Koh Samui, Koh Phangan and Koh Tao. Tue–Fri 17:00–20:00 · Sat–Sun 10:00–15:00 (UTC+7)
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Dr. Krida Uakridathikarn (Dr. Kris)
Board-certified family physician with certificate training in clinical sexology and sexual medicine. He works at Suratthani Hospital and provides sexual health, hormone and LGBTQ+ inclusive care at Dr. Kris Clinic. Profile and CV
References
- CDC STI Guidelines: Syphilis
- CDC STI Guidelines: Latent Syphilis
- CDC STI Guidelines: Screening Recommendations
- WHO: Sexually transmitted infections; estimates for 2020/2022
Keep reading
Main guide: HIV & STI prevention
Which STI Tests Do You Need, and When?
Gonorrhoea and Chlamydia: Symptoms, Testing and Proper Treatment
Genital Herpes: Symptoms, Testing, Treatment and Living With ConfidenceThis article is general education, not personal medical advice or a promise of results. Diagnosis and treatment require assessment by a doctor. Content reflects the cited sources as of the update date.