Syphilis is a sexually transmitted infection (STI) caused by the spiral-shaped bacterium Treponema pallidum. The infection progresses through distinct stages, beginning with the formation of a localized lesion known as a chancre. This chancre marks the primary stage of the disease and is the point of highest infectivity. Identifying this lesion early allows for highly effective treatment and prevents the infection from advancing into more damaging later stages. When transmitted through oral contact, the chancre can develop directly on the tongue or other tissues within the mouth.
The Primary Stage Oral Chancre
A primary syphilis chancre on the tongue results from the bacteria entering the body through microscopic breaks in the mucous membranes during oral sexual activity. This lesion typically appears approximately three weeks following exposure, although the incubation period can range anywhere from 10 to 90 days. The lesion begins as a small, raised bump that quickly erodes to form an ulceration, which is the characteristic chancre.
A chancre on the tongue is usually a single lesion, measuring about one to two centimeters in diameter. Its defining physical characteristic is its firm, indurated base and clean, non-pustular surface. These features make the sore feel hard to the touch, often described as having a cartilaginous or button-like texture.
The lesion is generally round or oval and often presents as a reddish, purplish, or sometimes brownish ulcer. Unlike most common mouth sores, the syphilis chancre is classically painless, which can lead to it being easily overlooked, especially if located on the posterior tongue or tonsil. This lack of pain contributes to the spread of the infection, as the lesion is highly contagious and teeming with T. pallidum bacteria.
Despite its infectious nature, the chancre will spontaneously heal within three to six weeks, even without medical intervention. This natural healing is misleading and does not mean the infection has been cleared from the body. The disappearance of the chancre marks the end of the primary stage and the beginning of the systemic spread of the bacteria.
Progression of Untreated Syphilis
The bacteria begin to disseminate throughout the body immediately after the initial infection. Once the chancre heals, the infection transitions into the secondary stage, typically occurring between four and ten weeks after the first sore appeared. This phase is characterized by systemic symptoms.
A widespread, non-itchy rash is the hallmark of secondary syphilis, frequently involving the palms of the hands and the soles of the feet. Other common symptoms include a generalized flu-like illness, which may involve fever, sore throat, fatigue, and swollen lymph nodes throughout the body. Oral manifestations can reappear during this stage as moist, grayish-white patches, known as mucous patches, which are highly infectious and can occur on the tongue or inner cheeks.
If the secondary stage is left untreated, the symptoms will eventually resolve, and the infection will enter the latent stage. Latent syphilis is an asymptomatic period where the bacteria remain in the body, often lasting for many years. Despite the lack of symptoms, the infection is still present and requires treatment to prevent future complications.
Approximately 15 to 30 percent of untreated individuals will eventually progress to tertiary syphilis, the most destructive stage. This late-stage disease can occur decades after the initial infection, causing severe damage to major organ systems. Manifestations include neurosyphilis (affecting the brain and nervous system), cardiovascular syphilis (damaging the heart and blood vessels), and gummatous syphilis (characterized by soft, tumor-like growths called gummas that can appear on the skin, bones, or internal organs).
Diagnosis and Testing Methods
Confirming a syphilis diagnosis relies on a combination of direct detection and serological testing. For an active chancre on the tongue, a healthcare provider may collect fluid from the lesion for dark-field microscopy. This technique allows for the direct visualization of the characteristic corkscrew-shaped T. pallidum bacteria, which exhibit rapid motility.
Dark-field microscopy provides an immediate result, which is beneficial since serological blood tests may not be reactive in the earliest days of the primary stage. However, this method must be interpreted with caution for oral lesions because non-pathogenic, similar-looking bacteria naturally reside in the mouth. Therefore, more specific methods, such as direct fluorescent antibody testing or polymerase chain reaction (PCR) on the lesion sample, are sometimes utilized.
The most common diagnostic approach involves serological blood tests, which detect antibodies produced by the immune system. Testing typically begins with a non-treponemal test, which measures general antibody activity. If this screening test is reactive, a more specific treponemal test is used to confirm the presence of antibodies specific to the syphilis bacterium. Common tests include:
- Rapid Plasma Reagin (RPR)
- Venereal Disease Research Laboratory (VDRL)
- Fluorescent Treponemal Antibody Absorption (FTA-ABS)
- T. pallidum Particle Agglutination (TP-PA) assay
Standard Medical Treatment
The standard treatment for early-stage syphilis is an antibiotic regimen utilizing penicillin. The preferred medication is Benzathine Penicillin G, administered as a single intramuscular injection of 2.4 million units for primary, secondary, or early latent syphilis. This single dose is curative in early cases.
For patients with a confirmed penicillin allergy, the first-line alternative treatment is usually doxycycline. This medication is taken orally at 100 milligrams twice a day for 14 days to clear the infection.
Penicillin-allergic patients whose compliance with oral medication or follow-up cannot be assured may require a desensitization process to safely receive penicillin, as it remains the most reliable treatment. Following treatment, all patients must undergo regular follow-up serological testing to ensure the infection has been eradicated. Monitoring typically involves repeating the non-treponemal RPR or VDRL test at six and twelve months post-treatment. A four-fold reduction in the antibody titer (e.g., from 1:32 to 1:8) confirms an adequate response and indicates a successful cure.