Syphilis is a complex, multi-stage bacterial infection. It is a systemic disease, meaning that after the initial infection, the bacteria can spread throughout the body and affect multiple organ systems, including the heart, brain, and nervous system. The disease is known for progressing through distinct stages, each with its own set of signs and symptoms. A key and dangerous feature of syphilis is its ability to enter a long latent (hidden) period after the initial stages, leading an infected person to falsely believe they are cured while the bacteria silently persist in their body.

To understand the progression of untreated syphilis, it can be helpful to think of it as a four-act play:

• Act I: Primary Syphilis. The initial invasion, characterized by a single, painless sore (a chancre) that appears at the site of infection. This “beachhead” disappears on its own, suggesting the conflict is over.
• Act II: Secondary Syphilis. The infection spreads throughout the body. This is marked by a widespread skin rash (classically on the palms and soles), fever, and swollen glands. This stage also resolves without treatment, reinforcing a false sense of security.
• Act III: Latent Syphilis. This is a long period of silent occupation. There are no signs or symptoms, but the bacteria are still present and are slowly preparing for the final stage. This can take years or decades.
• Act IV: Tertiary Syphilis. This is the final, destructive assault. Years after the initial infection, the bacteria cause severe damage to the body’s critical infrastructure—the brain, nervous system, heart, and blood vessels, leading to permanent disability and death.

Clinically, I’ve seen that many patients diagnosed with syphilis were completely unaware they had it, early stages may cause only mild or painless symptoms, so it’s often missed without regular STI screening.

Syphilis is caused by a specific type of bacterium called Treponema pallidum. This is a spirochete, a type of bacterium with a unique, corkscrew-like shape and a rotating motility. This spiral structure allows the bacterium to effectively burrow through mucous membranes and enter the bloodstream and lymphatic system, from where it can travel to virtually any organ in the body. The damage in the later stages of the disease is caused by the body’s chronic inflammatory response to the persistent presence of these bacteria in the tissues.

In my experience, many patients assume STIs must cause visible or painful symptoms. But syphilis challenges that assumption, especially in the latent or early stages when symptoms can be minimal or completely absent.

Syphilis is a sexually transmitted infection. It is crucial to understand how it is and is not spread to reduce both transmission and stigma.

Primary Mode of Transmission

Syphilis is transmitted from one person to another through direct contact with a syphilitic sore, known as a chancre. These sores occur mainly on the external genitals, vagina, anus, or in the rectum, but can also appear on the lips and in the mouth.

• Transmission occurs during vaginal, anal, or oral sex.
• Because the sores can be in hidden places and are often painless, a person may not know they are infectious.

Other Modes of Transmission

• Congenital Syphilis: A pregnant woman with syphilis can pass the infection to her unborn baby through the placenta. This is a very serious condition with devastating consequences for the infant.
• Syphilis is not spread by casual contact, such as from toilet seats, doorknobs, swimming pools, or sharing eating utensils or clothing.

I’ve often seen patients express disbelief “But I didn’t see anything unusual” which is why routine STI screening is especially critical in sexually active individuals, even those in long-term relationships.

Syphilis progresses in stages, each with its own set of symptoms. The stages can overlap, and symptoms may not appear in the expected order. In some cases, people are asymptomatic but still infectious.

Primary Syphilis

The first sign of syphilis is the appearance of a chancre.

• Appearance: It is typically a single, firm, round, and painless sore.
• Location: It appears where the bacteria entered the body.
• Timeline: The chancre appears anywhere from 10 to 90 days (average 21 days) after exposure.
• Course: Even without treatment, the chancre will heal on its own within 3 to 6 weeks, but the infection remains and will progress to the next stage.

Secondary Syphilis

This stage begins several weeks to months after the chancre has healed. It is characterized by signs that the infection has spread throughout the body.

• The Rash: The most common sign is a non-itchy skin rash. It can appear on one or more areas of the body and has a classic presentation when it affects the palms of the hands and the soles of the feet, appearing as rough, red or reddish-brown spots.
• Other Symptoms: This stage can also be accompanied by fever, swollen lymph glands, sore throat, patchy hair loss, weight loss, and muscle aches.
• Course: Like the primary stage, the symptoms of secondary syphilis will also resolve on their own without treatment, but the bacteria remain, and the disease enters the latent stage.

Latent Syphilis

This is the “hidden” stage where there are no visible signs or symptoms of the infection.

• Early Latent: The period up to one year after the secondary stage ends.
• Late Latent: The period after one year. The person is generally not considered contagious at this stage, but the infection is still damaging the body. This stage can last for the rest of the person’s life, or it can progress to the final, tertiary stage.

Tertiary (Late) Syphilis

This destructive stage can occur 10 to 30 years after the initial infection in about 15-30% of untreated individuals. It can cause severe damage to multiple organ systems.

• Neurosyphilis: The infection invades the brain and nervous system, causing dementia, paralysis, blindness, numbness.
• Cardiovascular Syphilis: The bacteria damage the aorta, the body’s main artery, leading to the formation of aneurysms that can rupture.
• Gummatous Syphilis: Formation of destructive rubbery lesions (gummas) in the skin, bones, and organs.

Patients often tell me they were more afraid of HIV or gonorrhea and didn’t realize syphilis could be so damaging long-term. Raising awareness about the stages and severity is often part of the counseling conversation.

When a pregnant woman with syphilis passes the infection to her baby during pregnancy, it is known as congenital syphilis. This can have devastating consequences for the infant. Congenital syphilis can lead to miscarriage, stillbirth or death of the baby shortly after birth.

Babies born with congenital syphilis can have a wide range of health problems, including:

• Skin rashes
• Bone deformities
• Severe anemia
• Jaundice and an enlarged liver and spleen
• Neurological problems, including blindness, deafness, and meningitis.

Routine screening for syphilis is a standard and essential part of prenatal care. If a pregnant woman is diagnosed with syphilis, she can be treated with penicillin, which will cure her infection and, in most cases, prevent the transmission to her baby.

Because its symptoms can be so varied, a diagnosis of syphilis is confirmed with specific tests.

• Blood Tests: This is the mainstay of diagnosis. There are two types of blood tests:
  • Screening Tests (Nontreponemal Tests): These tests, such as the VDRL and RPR, detect the antibodies the body produces in response to the damage caused by the infection.
  • Confirmatory Tests (Treponemal Tests): These tests, such as the TP-PA and FTA-ABS, detect antibodies that are specific to the T. pallidum bacterium itself.
• Direct Testing: In the primary or secondary stage, a doctor can take a sample of fluid from a sore and use a special technique called dark-field microscopy to look for the live spirochete bacteria.
• Lumbar Puncture: If neurosyphilis is suspected, a doctor will perform a lumbar puncture to collect a sample of cerebrospinal fluid to test for evidence of the infection.

In my clinical experience, explaining why two tests are needed often helps build trust “screening plus confirmation” is standard in syphilis because false positives can occur with some initial tests.

Syphilis is curable in all stages with the right antibiotics, although organ damage from late-stage syphilis may be irreversible.

• Penicillin: Penicillin injections are the treatment of choice for all stages of syphilis. It is the only recommended treatment for pregnant women and neurosyphilis.
  • For early-stage syphilis, a single intramuscular injection of a long-acting form of penicillin is usually sufficient to cure the infection.
  • For late-stage syphilis, a longer course of treatment, typically three weekly injections, is required.
• Alternatives: For individuals with a penicillin allergy (who are not pregnant), other antibiotics like doxycycline can be used.
• Jarisch-Herxheimer Reaction: It is common for people to experience a temporary reaction within hours of their first penicillin injection. This includes fever, chills, headache, and muscle aches. This is a sign that the antibiotic is working and killing large numbers of the bacteria, which triggers an inflammatory response.

It is crucial that all sexual partners of a person diagnosed with syphilis are also notified and treated to prevent reinfection and further spread of the disease.

One thing I always emphasize is that treatment doesn’t offer future protection, syphilis can be cured but not prevented once exposed. Prevention through safe sex and regular testing is essential moving forward.

Syphilis remains a significant public health concern, a “Great Pretender” that can cause devastating and permanent damage if left untreated. Its ability to disappear for years can lull individuals into a false sense of security, while the bacteria continue to inflict silent damage on the body. However, the story of syphilis in the modern era is one of great hope. It is easily diagnosed with reliable blood tests and, most importantly, is completely curable with penicillin, one of the oldest and most effective tools in medicine. Clinically, I always remind patients that syphilis is no longer a “disease of the past”. It’s still very present today, and the good news is that with simple treatment and good communication, we can catch it early and protect long-term health.

Centers for Disease Control and Prevention (CDC). (2024). Syphilis – Detailed Fact Sheet. Retrieved from https://www.cdc.gov/std/syphilis/stdfact-syphilis-detailed.htm

World Health Organization (WHO). (2022). Syphilis. Retrieved from https://www.who.int/news-room/fact-sheets/detail/syphilis

National Institutes of Health, National Institute of Allergy and Infectious Diseases (NIAID). (2021). Syphilis. Retrieved from https://www.niaid.nih.gov/diseases-conditions/syphilis