Syphilis is a complex sexually transmitted infection (STI) caused by the spiral-shaped bacterium, Treponema pallidum subspecies pallidum. This disease has historically posed a significant public health challenge and continues to do so globally.
Understanding Treponema Pallidum
Treponema pallidum is a delicate, helically coiled bacterium, typically measuring 6 to 15 micrometers in length and 0.1 to 0.2 micrometers in width. Its flexible structure and undulating motion allow it to penetrate host tissues effectively. This spirochete is an obligate parasite, meaning it relies entirely on a host for survival and cannot be cultured in a laboratory setting.
The bacterium primarily obtains glucose from its host for energy. Treponema pallidum can rapidly penetrate the skin, causing systemic infection. It can also evade host immune defenses.
How Syphilis is Transmitted
Syphilis is primarily transmitted through direct contact with an active syphilis sore during sexual activities, including vaginal, anal, and oral sex. The bacterium enters the body through mucous membranes or small breaks in the skin. The risk of transmission depends on factors such as the frequency of sexual contact, the type of sexual activity, and the stage of syphilis in the infected individual.
Transmission can also occur vertically from a pregnant person to their baby during pregnancy, leading to congenital syphilis. This can result in severe health problems for the infant, including miscarriage, stillbirth, or early infant death. Less common routes include direct contact with an active lesion on the skin or through shared needles.
The Stages and Signs of Syphilis
Syphilis progresses through distinct stages, each with characteristic signs.
Primary Syphilis
The first sign of primary syphilis is usually a chancre, a painless open sore that develops where the bacteria entered the body. These chancres commonly appear on the genitals, mouth, or rectum. They heal on their own within three to six weeks, but the infection remains present and can still be transmitted. Swollen lymph nodes may also occur near the chancre.
Secondary Syphilis
Secondary syphilis symptoms begin after the primary chancre appears. This stage is characterized by a systemic spread of the bacterium, leading to varied symptoms. A common sign is a non-itchy skin rash that can appear anywhere on the body, frequently involving the palms of the hands and soles of the feet.
Other symptoms can include fever, swollen lymph nodes, sore throat, patchy hair loss, headaches, muscle aches, and a general feeling of malaise. Moist, wart-like patches called condylomata lata may develop in warm, moist areas like the genitals or skin folds. Mucous patches, which are sores, can appear in or around the mouth, vagina, or penis. These lesions are highly contagious.
Latent Syphilis
Following secondary syphilis, the infection enters a latent stage, where there are no visible signs or symptoms. This stage can be divided into early latent (infection within the past year) and late latent (infection for more than a year or of unknown duration). Despite the absence of symptoms, the infection can still be present for many years, continuing to potentially damage internal organs if left untreated.
Tertiary Syphilis
If syphilis remains untreated, it can progress to tertiary syphilis, which may develop years, even decades, after the initial infection. This late stage can lead to severe and potentially fatal complications affecting various organ systems. Neurosyphilis occurs when the infection spreads to the brain and nervous system, causing symptoms such as headaches, changes in mental state, problems with coordination, vision issues, or hearing loss.
Cardiovascular syphilis can affect the heart and blood vessels, potentially leading to aneurysms or valve disease. Gummatous syphilis involves the formation of gummas, which are soft, tumor-like inflammatory lesions that can appear on the skin, bones, or internal organs, causing destructive tissue damage. The symptoms of tertiary syphilis vary widely depending on the affected organs, making diagnosis challenging.
Congenital Syphilis
Congenital syphilis occurs when Treponema pallidum is transmitted from a pregnant person to their fetus. This can result in serious consequences for the baby, including miscarriage, premature birth, stillbirth, or severe health problems at birth or later in life. Early congenital syphilis signs, apparent before two years of age, may include mucocutaneous lesions, bone inflammation, anemia, and an enlarged liver and spleen. Late congenital syphilis, manifesting after two years, can involve issues like blindness, tooth deformities, deafness, and neurosyphilis.
Diagnosing and Treating Syphilis
Diagnosing syphilis involves clinical evaluation and laboratory tests. The primary diagnostic methods are blood tests. Non-treponemal tests, such as RPR or VDRL, are used for initial screening. These tests detect antibodies produced by the body in response to tissue damage.
If a non-treponemal test is reactive, a treponemal-specific test, such as FTA-ABS or TP-PA, confirms the diagnosis by detecting antibodies specific to T. pallidum. In cases where neurosyphilis is suspected, a lumbar puncture may be performed to analyze cerebrospinal fluid for evidence of infection in the nervous system. Direct visualization of spirochetes using dark-field microscopy from a lesion can also confirm primary syphilis.
Treatment for syphilis, regardless of the stage, primarily involves penicillin. Penicillin G benzathine, administered via injection, is the preferred medication because it effectively kills the Treponema pallidum bacteria. The dosage and number of injections vary depending on the stage of syphilis.
For early-stage syphilis (primary, secondary, or early latent), a single injection of penicillin may be sufficient. For later stages, such as late latent or tertiary syphilis, multiple injections administered over several weeks are typically required. Pregnant individuals with syphilis, or those with neurosyphilis, are exclusively treated with penicillin, even if they have a penicillin allergy, in which case a desensitization process may be undertaken. After treatment, follow-up blood tests are conducted to ensure the infection has been successfully cured, with a significant decline in quantitative non-treponemal test titers expected within six to 24 months.
Preventing Syphilis
Preventing the spread of Treponema pallidum involves several practical strategies. Consistent and correct use of barrier methods during sexual activity, such as condoms for vaginal or anal sex and dental dams for oral sex, significantly reduces the likelihood of transmission. Condoms work by preventing contact with syphilis sores, though sores may sometimes occur in areas not covered by a condom.
Regular sexually transmitted infection (STI) screening is another important preventive measure, particularly for sexually active individuals and those with multiple partners. Pregnant individuals should be screened for syphilis at their first prenatal care visit to prevent congenital syphilis, with prompt treatment if the test result is positive. Partner notification and treatment are also important public health actions, ensuring that sexual partners of infected individuals are informed, tested, and treated to interrupt further transmission chains. Avoiding the sharing of needles is a general practice for preventing the spread of bloodborne infections.