Syphilis

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, prevalence and risk groups

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), 1078 new diagnoses were reported for Switzerland in 2022.

The majority of those affected are men (88 percent), especially homosexual men (MSM) or people with frequently changing sexual partners.

Causes and risk factors of syphilis

The cause of syphilis (lues) is an infection with the bacterium Treponema pallidum. This pathogen belongs to the spirochete family and is only transmitted from person to person.

In most cases, syphilis is transmitted through unprotected sexual contact – this includes vaginal, anal and oral sex. Infection occurs via tiny injuries to the skin or mucous membranes through which the bacteria enter the body. Intensive kissing can also lead to infection in individual cases if lesions are present in the mouth.

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.

How do you recognize syphilis? Symptoms by stage

A syphilis infection can cause very different symptoms – depending on the stage and severity of the disease. It often begins unnoticed or with very mild symptoms. In more than half of cases, syphilis is asymptomatic or even asymptomatic in the early stages, which makes diagnosis difficult. A syphilis test is therefore also useful without symptoms if there was an increased risk of infection – for example through unprotected sexual intercourse, changing partners or suspected infection in the sexual partner.

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. The incubation period for syphilis – i.e. the time between infection and the first symptoms – is usually 21 days, but can extend to 90 days. A painless, hard nodule initially forms at the site where the pathogens have entered the body. As syphilis is usually transmitted during sexual intercourse, this skin change often occurs 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 – the so-called hard chancre (ulcus durum). 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

Syphilis usually enters the secondary stage two to three months after infection. The pathogens enter the entire body via the lymphatic system and the blood. In addition to swelling of the lymph nodes, secondary syphilis can cause flu-like symptoms such as fever, loss of appetite, pharyngitis, weight loss or headaches, muscle and joint pain. Red blotchy, sometimes palpable skin and mucous membrane changes 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 a quarter of untreated syphilis cases progress to the tertiary stage years after infection – also known as late syphilis or tertiary syphilis. At this stage, chronic inflammation occurs that affects a wide variety of body systems.

Damage to the internal organs, blood vessels, cardiovascular system, bones, muscles and skin is typical. The nervous system can also be affected, which can manifest itself in sensory disturbances, dementia or paralysis. Another characteristic feature of late syphilis are so-called gummas – rubbery lumps in the skin or organs that can grow over years and cause considerable tissue damage.

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 as well as a disturbed gait pattern. 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.

Pregnant women are therefore recommended to have a syphilis test carried out at an early stage as part of their check-ups.

Diagnosis of syphilis

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: protection and early detection

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”. Condoms offer a certain degree of protection, but not complete protection, especially during vaginal or anal intercourse with frequently changing sexual partners.

Syphilis can also be transmitted without sexual intercourse – for example from an infected mother to her unborn child. A timely diagnosis of syphilis during pregnancy is therefore crucial. Appropriate syphilis tests (screening examinations) are recommended 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

The course of the disease depends heavily on the stage of the disease. In early stages such as primary or secondary syphilis, the infection can also heal without treatment in individual cases. If the disease is recognized in time, syphilis can be treated excellently.

However, the disease can sometimes recur even after years of freedom from 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.

However, if diagnosed early and treated consistently, syphilis can be cured – and the course and prognosis are good.

Treatment of syphilis

The treatment of choice for syphilis is the antibiotic penicillin (benzathine benzylpenicillin), which is usually administered as an injection into the gluteal muscle. The duration of therapy depends on the stage of the disease and any concomitant illnesses. If the nervous system, eyes or ears are involved, penicillin is administered as an infusion.