Syphilis

Syphilis is almost always diagnosed with a blood test, a quick draw or finger-prick that detects antibodies produced in response to Treponema pallidum infection. Two types of tests are used: non-treponemal tests (RPR or VDRL) screen for general antibody activity and produce a titer that tracks disease activity over time; treponemal tests (TPPA, FTA-ABS or EIA) confirm that the antibodies are specific to syphilis. Both are usually done together because neither type alone tells the whole story. If you have an active sore, a clinician can also swab it for direct microscopy or PCR, which detects the bacteria before the antibody tests become reactive.

The primary syphilis sore, called a chancre, is typically a single, firm, round ulcer with clean, raised edges and a smooth base. What makes it so deceptive is that it is almost always painless: no tenderness, no discharge, no bleeding. It appears at the site where T. pallidum entered the body, usually on the genitals, anus, lips or throat, and it often hides inside the vagina, rectum or throat where you can't see or feel it. The sore heals on its own in 3–6 weeks, which people routinely interpret as recovery, but the bacteria have simply moved deeper. If you notice a painless ulcer anywhere on your genitals or mouth, get a blood test immediately rather than waiting to see if it resolves.

Yes: syphilis is completely curable with penicillin, which has been the treatment of choice for over 70 years with zero documented resistance. Primary, secondary and early latent syphilis (under one year) requires a single intramuscular injection of benzathine penicillin G. Late latent or unknown-duration syphilis requires three weekly injections. Neurosyphilis requires intravenous penicillin G given in a hospital or infusion setting for 10–14 days. The critical limitation: penicillin cures the infection and stops further damage, but it cannot reverse damage already done. Neurosyphilis that has caused dementia, aortic disease that has caused an aneurysm, or congenital infection that has caused deafness are not reversed by treatment. Getting tested and treated early is what prevents those outcomes.

Yes: latent syphilis, which has no symptoms at all, is one of the most dangerous states to be in precisely because it is silent. The bacteria are not dormant in the sense of being inactive; T. pallidum persists in tissues throughout the body and, in 25–30% of untreated people, drives the development of tertiary disease years to decades later. Tertiary syphilis includes neurosyphilis (progressive dementia, loss of coordination), cardiovascular disease (aortic aneurysm, heart failure) and gummatous disease (destructive granulomas in skin, bone and organs). By the time those complications become symptomatic, significant irreversible damage has already occurred. The latent stage is also the time when a pregnant person can transmit the infection to a fetus. Feeling fine is not the same as being fine, a blood test is the only way to know.

The Jarisch-Herxheimer reaction is a predictable side effect of syphilis treatment that is often confused with a penicillin allergy, they are completely different things. It occurs when penicillin kills large numbers of Treponema pallidum rapidly, releasing bacterial antigens that trigger a systemic inflammatory response. Within 2–8 hours of the first treatment dose, you may develop fever (sometimes high), rigors, headache, muscle aches, sweating and a temporary flare of the syphilis rash. It typically peaks at about 8 hours and resolves within 24 hours. Manage it with acetaminophen and rest, and stay hydrated. It is more pronounced with primary and secondary syphilis than with latent disease. In pregnancy, the fever can trigger uterine contractions and fetal distress, which is why treatment in pregnant patients is given in a monitored setting. Experiencing this reaction does not mean penicillin is harming you, it means the treatment is working.

Treponema pallidum crosses the placenta readily and can infect the fetus at any point during pregnancy, though transmission is most efficient, approaching 80%, with untreated primary or secondary maternal syphilis in the first or early second trimester. The results are severe: miscarriage, stillbirth, premature birth, and in liveborn infants, a constellation of findings called congenital syphilis including nasal discharge, widespread rash, hepatosplenomegaly, severe anemia, bone lesions and, appearing years later, Hutchinson teeth, corneal scarring and hearing loss. In 2023, 3,882 U.S. newborns were diagnosed with congenital syphilis and 279 died. Every one of those outcomes is preventable: a blood test at the first prenatal visit and a penicillin injection stops transmission to the baby. If you are pregnant and have not been tested for syphilis, get tested today.

Yes. Syphilis is transmitted by direct contact with a sore: and chancres can form on the lips, tongue, throat and tonsils as readily as they form on genitalia. Performing oral sex on a partner who has a genital sore, or receiving oral sex from a partner who has an oral sore, both transmit syphilis. The oral chancre is often smaller and less visible than a genital one, and it is painless, so people with oral syphilis frequently don't know they have it. If your testing includes a throat swab for gonorrhea or chlamydia, it does not test for syphilis, you need a blood test specifically for syphilis.

The relationship between syphilis and HIV runs in both directions. An open syphilis sore substantially increases both the acquisition and transmission risk for HIV, the disrupted epithelium and local inflammation at a chancre are a direct entry point for HIV. Conversely, in people who already have HIV, syphilis is more likely to cause unusual or accelerated manifestations: neurosyphilis and ocular syphilis occur more commonly and can appear earlier in the disease course than in HIV-negative individuals. Treatment for syphilis in people with HIV is generally the same as standard CDC regimens, but follow-up monitoring is more intensive because treatment response may be slower. People with HIV and syphilis coinfection should have careful clinical and serological follow-up at 3, 6, 9, 12 and 24 months.

Neurosyphilis is invasion of the central nervous system by Treponema pallidum, and it can happen at any stage of syphilis, it is not exclusively a late or tertiary complication. Early neurosyphilis presents as aseptic meningitis: severe headache, stiff neck, fever and cranial nerve involvement (facial weakness, double vision, hearing loss). Late neurosyphilis, developing after years of untreated infection, produces two classic syndromes: general paresis, a progressive dementia with personality change and psychiatric symptoms; and tabes dorsalis, a degeneration of the posterior spinal cord causing stabbing leg pains, loss of position sense and an unsteady gait. Ocular syphilis (uveitis, retinitis, optic neuritis) is classified as neurosyphilis for treatment purposes and can cause permanent blindness. Neurosyphilis is diagnosed by examining spinal fluid (lumbar puncture) and is treated with high-dose IV penicillin G for 10–14 days, a single IM injection is not adequate.

The same infection cannot come back after successful treatment, penicillin permanently clears the bacteria. But syphilis confers no lasting immunity, so you can be re-infected from a new or untreated partner as easily as if you had never had it. Re-infection is common, particularly in communities with high syphilis rates and among people with multiple partners. Clinically, re-infection looks identical to a new infection: a rising RPR titer, often with symptoms, even in someone who was treated and confirmed cured. This is why follow-up blood testing at 6, 12 and 24 months matters: a rising titer indicates re-infection (or less commonly, treatment failure) and requires a new course of treatment.

The contagiousness of syphilis depends heavily on the stage. Primary syphilis, when active chancres are present, is highly contagious through sexual contact with those sores. Secondary syphilis, with its disseminated rash, condylomata lata and mucous patches, is also highly contagious; the condylomata lata in skin folds are particularly infectious because they are moist and teeming with spirochetes. Early latent syphilis (less than one year since infection) carries a risk of sexual transmission and also a risk of relapse to secondary symptoms. Late latent syphilis (more than one year) is not considered sexually transmissible. Tertiary syphilis is not contagious. Critically, a pregnant person with any stage of syphilis can transmit it to the fetus, including late latent. After a single IM penicillin injection, the risk of sexual transmission drops rapidly, but avoid sex until the treatment is complete and the sore has healed.