Syphilis is a chronic bacterial infectious disease that is mainly transmitted through unprotected sexual contact. Men who have sex with men (MSM) and people with changing sexual partners are particularly at risk. Women are affected much less frequently. Treatment is primarily with antibiotics. If left untreated, syphilis can lead to severe organ damage.

Overview: What is syphilis?

Syphilis, also known as lues, is a chronic infectious disease caused by the bacterium Treponema pallidum. This pathogen is mainly transmitted through unprotected sexual contact (oral, anal, vaginal sex) via tiny injuries to the mucous membrane or skin. Syphilis is therefore considered a sexually transmitted disease or venereal disease.

Syphilis – frequency and age

Syphilis is spread worldwide. The number of people affected has risen sharply in recent years – even in welfare states such as Switzerland. According to the Federal Office of Public Health (FOPH), 885 new diagnoses were reported in Switzerland in 2018.

Of the new syphilis cases, the majority involved men (88 percent). Homosexual men (MSM) or people with several changing sexual partners have an increased risk of infection. Around 70 out of 100 patients are homosexual.

Syphilis: causes and risk factors

The cause of syphilis (lues) is an infection with Treponema pallidum from the spirochete family. This type of bacteria can only be passed on from person to person.

In most cases, syphilis is transmitted through unprotected sexual intercourse. The risk of contracting the disease from an infected person is around 30 percent. Infection is also possible through oral and anal sex or kissing. The pathogens enter the body through the smallest injuries to the mucous membranes or skin during sexual contact.

In rare cases, pregnant women can also infect their unborn child via the placenta or transmit the germ to the baby during birth.

Transmission through blood transfusions is also theoretically possible. However, this risk is very low, as blood reserves are now closely examined.

Symptoms: Syphilis

A syphilis infection can cause various symptoms. How these manifest themselves also depends on the form of the disease and the respective stage.

It is important to know that syphilis is asymptomatic or has few symptoms in more than half of all cases. Testing is therefore also recommended for people without symptoms if the person was at risk of infection.

Symptoms of early syphilis

Syphilis in the initial phase is referred to as early syphilis and progresses in two stages:

Primary stage

There are often no symptoms immediately after infection. It usually takes 14 to 24 days for a painless, hard nodule to develop at the site where the pathogens have penetrated. As the germ is mainly transmitted through sexual contact, it can occur on the penis, labia, vagina, anus or mouth. As it progresses, the nodule hardens and develops into an ulcer with swollen, rolled edges and a sunken center. Within a week, the neighboring lymph nodes often swell as well. The ulcer usually does not cause any pain and usually heals on its own after four to six weeks. As a result, syphilis often remains undetected and untreated at this stage.

Secondary stage

Two to three months after infection, syphilis enters the secondary stage. The pathogens enter the entire body via the lymphatic system and the blood. In addition to swelling of the lymph nodes, flu-like symptoms such as fever, loss of appetite, pharyngitis, weight loss or headache, muscle and joint pain can occur at this stage. Skin and mucous membrane changes including scaly, purulent blisters or weeping pustules are also typical. Hair loss sometimes occurs. Syphilis can also affect organs and cause inflammation of the liver, eyes or kidneys. The symptoms at this stage can persist for years or flare up again and again. In every third person affected, syphilis heals spontaneously in the secondary stage. If those affected remain symptom-free for years, they are said to have latent syphilis. In the latent stage, those affected are only slightly or no longer infectious to others.

Symptoms of late syphilis

Around one in four patients with untreated early-stage syphilis develops late-stage syphilis one to ten years after infection. In this tertiary stage, various symptoms can occur that affect the organs, blood vessels, cardiovascular system, bones, muscles and skin. The nervous system can also be affected, possibly resulting in sensory disturbances or dementia. In addition, tumors with a rubbery consistency (gummas) can occur on the skin and organs in the tertiary stage. These nodules can grow up to several centimeters in size and slowly increase in size.

Symptoms of neurosyphilis

If the bacteria penetrate the central nervous system, experts speak of neurosyphilis (from neuro = affecting the nerves). This can happen in the first year of infection during early syphilis or later during late syphilis. Around one in two people with the disease do not experience any recognizable symptoms. Early neurosyphilis typically affects the eyes (visual impairment), the ears (deafness) or the meninges. In the case of untreated late neurosyphilis, the so-called parenchymatous form of syphilis can develop after years, which attacks the brain tissue. Possible symptoms include

  • Memory loss,
  • Headache,
  • Insomnia,
  • Failures of the facial muscles,
  • Symptoms of paralysis,
  • Perceptual disorders or

After 25 to 30 years, a so-called tabes dorsalis can develop. In this final stage, nerve sheaths, nerve roots and nerve nodes are destroyed, which is noticeable, among other things, by a disturbed sensation of pain and temperature. A complication can be an ulcer on pressure points of the foot (malum perforans pedis).

Symptoms of congenital syphilis

In the early syphilis stage, infected women can transmit the pathogen to their child during pregnancy or childbirth. It is therefore important to test women who want to become pregnant for syphilis. This congenital syphilis significantly increases the risk of premature birth or stillbirth. Without treatment, the risk of the newborn being born dead is 30 to 40 percent. Many infected newborns initially show no symptoms. Only in rare cases do symptoms such as breathing problems or water retention (edema) occur immediately after birth. Other symptoms may occur in the first two years of life. These include, for example, fever, colds, reduced drinking capacity, swelling of the lymph nodes, skin changes, enlargement of the liver and spleen or intestinal inflammation. If childhood syphilis is not treated, it can damage various parts of the body such as the central nervous system, eyes, ears, skin and mucous membranes, bones, teeth or shins.

Syphilis diagnosis

Syphilis diagnostics have been carried out at the USZ for many years. Around one in ten cases in Switzerland is detected in the accredited laboratory of the dermatology clinic. If syphilis is suspected, we can detect the pathogen directly. To do this, we take a sample from a weeping skin lesion. The DNA of the bacteria is then detected from the secretion using a molecular biological test developed by us. Another diagnostic option is a blood test (serology), which we carry out very frequently. If antibodies against the pathogen can be detected, this is an indication of an infection. After an infection with syphilis, it can take up to three months in extreme cases for the serology in the blood to become positive. If clinical suspicion persists, the serology must therefore be repeated after approximately one month if it is initially negative.

If it is suspected that the bacteria have already infected the central nervous system (neurosyphilis), we can perform a cerebrospinal fluid puncture. A small amount of cerebrospinal fluid is removed from the spinal cord and then examined.

Syphilis: prevention, early detection, prognosis

There is currently no vaccination that can prevent syphilis.

However, you can significantly minimize the risk of infection for yourself and others. The most important measure is “safer sex”. Of particular importance in this context is the use of condoms during sexual intercourse. This is particularly important with frequent, changing sexual partners. However, a condom only provides around 50 percent protection, as syphilis is often transmitted through oral sex or kissing.

As an expectant mother, you can prevent syphilis from being transmitted to your unborn child by having appropriate tests (screening examinations) carried out as part of maternity care. If a syphilis infection is detected, you should be treated immediately with an antibiotic to minimize the risk of transmission to your child.

Course and prognosis of syphilis

Syphilis can progress differently depending on the form and stage of the disease. In some cases, the disease heals itself. This is particularly the case with primary and secondary syphilis.

However, the disease can sometimes recur even after years without symptoms (latent syphilis). Possible consequences are severe nerve disorders, heart and bone changes as well as an infestation of internal organs.

If syphilis is only recognized and treated at an advanced stage, this has a negative impact on the prognosis. Any late damage, such as paralysis, can leave those affected in need of care for the rest of their lives.

With a timely diagnosis and consistent treatment, the course and prognosis are good.

Syphilis: Treatment

The treatment of choice for syphilis is the antibiotic penicillin (benzathine benzylpenicillin), which is administered as an injection into the gluteal muscle.