Syphilis is caused by bacteria called Treponema pallidum. This bacteria is a spirochete, a type of spiral-shaped bacteria. The bacteria gets in through skin or mucous membranes, replicates and then disseminates throughout the body. It is mainly a sexually transmitted infection. The incubation period between the initial infection and symptoms is 21 days on average.
Syphilis can also be contracted through:
- Oral, vaginal or anal sex involving direct contact with an infected area
- Vertical transmission from mother to baby during pregnancy
- Intravenous drug use
- Blood transfusions and other transplants (although this is rare due to screening of blood products)
Primary syphilis involves a painless ulcer called a chancre at the original site of infection (usually on the genitals).
Secondary syphilis involves systemic symptoms, particularly of the skin and mucous membranes. These symptoms can resolve after 3 – 12 weeks and the patient can enter the latent stage.
Latent syphilis occurs after the secondary stage of syphilis, where symptoms disappear and the patient becomes asymptomatic despite still being infected. Early latent syphilis occurs within two years of the initial infection, and late latent syphilis occurs from two years after the initial infection onwards.
Tertiary syphilis can occur many years after the initial infection and affect many organs of the body, particularly with the development of gummas and cardiovascular and neurological complications.
Neurosyphilis occurs if the infection involves the central nervous system, presenting with neurological symptoms.
Primary syphilis can present with:
- A painless genital ulcer (chancre). This tends to resolve over 3 – 8 weeks.
- Local lymphadenopathy
Secondary syphilis typically starts after the chancre has healed, with symptoms of:
- Maculopapular rash
- Condylomata lata (grey wart-like lesions around the genitals and anus)
- Low-grade fever
- Alopecia (localised hair loss)
- Oral lesions
Tertiary syphilis can present with several symptoms depending on the affected organs. Key features to be aware of are:
- Gummatous lesions (gummas are granulomatous lesions that can affect the skin, organs and bones)
- Aortic aneurysms
Neurosyphilis can occur at any stage if the infection reaches the central nervous system, and present with symptoms of:
- Altered behaviour
- Tabes dorsalis (demyelination affecting the spinal cord posterior columns)
- Ocular syphilis (affecting the eyes)
- Sensory impairment
Argyll-Robertson pupil is a specific finding in neurosyphilis. It is a constricted pupil that accommodates when focusing on a near object but does not react to light. They are often irregularly shaped. It is commonly called a “prostitutes pupil” due to the relation to neurosyphilis and because “it accommodates but does not react“.
Antibody testing for antibodies to the T. pallidum bacteria can be used as a screening test for syphilis.
Patients with suspected syphilis or positive antibodies should be referred to a specialist GUM centre for further testing.
Samples from sites of infection can be tested to confirm the presence of T. pallidum with:
- Dark field microscopy
- Polymerase chain reaction (PCR)
The rapid plasma reagin (RPR) and venereal disease research laboratory (VDRL) tests are two non-specific but sensitive tests used to assess for active syphilis infection. These tests assess the quantity of antibodies being produced by the body to an infection with syphilis. A higher number indicates a greater chance of active disease. These tests involve introducing a sample of serum to a solution containing antigens and assessing the reaction. A more significant reaction suggests a higher quantity of antibodies. The tests are non-specific, meaning they often produce false-positive results. There is a skill to both performing and interpreting the results of these tests.
All patients should be managed and followed up by a specialist service, such as GUM. As with all sexually transmitted infections, patients need:
- Full screening for other STIs
- Advice about avoiding sexual activity until treated
- Contact tracing
- Prevention of future infections
A single deep intramuscular dose of benzathine benzylpenicillin (penicillin) is the standard treatment for syphilis.
Alternative regimes and types of penicillin are used in different scenarios, for example, late syphilis and neurosyphilis. Ceftriaxone, amoxicillin and doxycycline are alternatives.
Last updated August 2020