Men's Health Education: In-depth Analysis of the Transmission Routes and Clinical Stages of Syphilis

Syphilis

Syphilis is a chronic sexually transmitted disease caused by Treponema pallidum. After infection, the spirochete quickly spreads throughout the body via the lymphatic system and bloodstream, invading various organs and producing a wide range of clinical symptoms and signs. Syphilis is primarily transmitted through sexual contact, but it can also be transmitted to the next generation via the placenta, resulting in congenital syphilis.

(I) Characteristics of the Pathogen

The spirochete that causes syphilis was discovered in 1905 by Schandinn and Hoffmann. The spirochete is 5–20 nm long and <0.2 nm in diameter, with 6–12 spirals. When unaffected by external factors, the spirals are regular. Because it is transparent and difficult to stain, it is also known as the pale spirochete.

The spirochete does not survive well outside the human body. Boiling, drying, soapy water, and common disinfectants easily kill it. It can be killed within 1–2 hours at 41–42°C, but can survive for several years at -78°C.

(II) Transmission Routes

1. Sexual Transmission
Sexual contact is the primary route of syphilis transmission. Untreated patients are most infectious in the first year after infection, as their skin and mucous membrane lesions contain a large number of Treponema pallidum bacteria, making them easily infected through skin and mucous membrane lesions of sexual contacts. Infectivity decreases as the disease progresses.

2. Transmission to the Fetus
Pregnant women with syphilis can infect their fetus through the placenta. It is generally believed that infection does not occur in the first four months of pregnancy, possibly due to the protective effect of the trophoblast. Untreated female syphilis patients with a disease course exceeding four years, although no longer infectious through sexual contact, can still transmit the disease to the fetus during pregnancy.

3. Other Transmission Routes
A small number of patients can be infected through routes other than sexual contact. Direct contact such as kissing and breastfeeding; indirect contact with contaminated daily necessities such as clothing, towels, tableware, and razors; and infection can also occur to healthcare workers and laboratory personnel due to negligence when handling patient specimens. Furthermore, early-stage syphilis patients can transmit the virus to others through blood transfusions when they are blood donors.

(III) Clinical Staging
Syphilis can be classified into acquired and congenital (transmitted from mother to child) syphilis based on the route of transmission, and into early and late syphilis based on whether it is infectious.

1. Early Syphilis
After Treponema pallidum invades the human body, it multiplies under the skin and mucous membranes, and quickly travels along the lymphatic vessels to nearby lymph nodes. After an incubation period of 2-4 weeks, an inflammatory reaction occurs at the site of invasion, called a chancre. The chancre will disappear naturally after several weeks, even without treatment. This period of time with the chancre is clinically termed primary syphilis. When a chancre appears, Treponema pallidum enters the bloodstream from the lymph nodes near the chancre and spreads throughout the body, infecting most tissues and organs. After a second incubation period of 6-8 weeks, symptoms such as low-grade fever, swollen lymph nodes, skin and mucous membrane rashes, meningitis, and other signs may appear. This stage is called secondary syphilis. Symptoms of secondary syphilis can disappear spontaneously without treatment, returning to a latent state known as asymptomatic syphilis. Although there are no clinical symptoms at this stage, the spirochetes remain hidden in the body's tissues and lymphatic system. Symptoms can reappear once the body's resistance decreases; this is clinically called relapsed secondary syphilis.

Primary and secondary syphilis are called early syphilis, with a course of less than 2 years. Early syphilis is highly contagious.

2. Late Syphilis
If primary and secondary syphilis patients do not receive effective treatment and the disease course lasts for more than 2 years, it is clinically called late syphilis or tertiary syphilis. Approximately 30%–40% of late-stage syphilis patients develop active syphilis, including damage to organs such as the heart, liver, and nervous system. Some patients may not exhibit symptoms of tertiary syphilis, but their serological test remains positive, a condition known as latent syphilis. In some patients, the serological titer gradually decreases, eventually becoming negative, and the syphilis resolves spontaneously.

(IV) Clinical Manifestations

1. Primary Syphilis
The main symptom is a chancre, which appears 2–4 weeks after unprotected sex. It mostly occurs in the genital area; in men, it is commonly found on the foreskin, coronal sulcus, frenulum, or glans penis; in homosexual men, it is commonly found in the anus, anal canal, or rectum; in women, it is most common on the labia majora and minora or cervix.

Several days after the appearance of the chancre, unilateral inguinal lymph node enlargement occurs, followed by enlargement on the other side. These lymph nodes are characterized by:
① being about the size of a fingertip, relatively hard, and scattered without fusing;

② being painless and tender;

③ having no redness, swelling, or heat on the overlying skin;

④ not suppurating;

⑤ containing spirochetes in the aspirate.

In the early stages of a chancre, most patients have a negative syphilis serological reaction. The positive rate gradually increases, and 7-8 weeks after the appearance of the chancre, all patients have a positive serological reaction.

2. Secondary Syphilis

This is the systemic symptom that appears after Treponema pallidum enters the bloodstream from the lymph nodes and spreads extensively throughout the body. It generally occurs 7-10 weeks after infection or 6-8 weeks after the appearance of the chancre. Early symptoms include flu-like syndrome (60%-90%) and generalized lymphadenopathy (50%-85%), skin and mucous membrane lesions, bone lesions, ocular syphilis, neurosyphilis, etc. 80%–95% of patients may experience skin and mucous membrane lesions, including rashes, condyloma lata, hair loss, syphilitic leukoplakia, and mucosal damage.

Skeletal damage: Periostitis and arthritis may occur, both characterized by more severe pain at night and rest, and milder pain during the day and during activity. It commonly occurs in the long bones of the limbs, but can also occur at the attachment points of skeletal muscles, such as the olecranon, iliac crest, and mastoid process. Exacerbations are often seen upon initial anti-syphilis treatment.

Ocular syphilis: Iritis, iridocyclitis, vasculitis, optic neuritis, and retinitis may occur.

Neurosyphilis: Often asymptomatic, but with abnormal changes in cerebrospinal fluid, such as increased protein, increased lymphocyte count, a positive VDRL test, and abnormal colloidal gold curves.

Meningitis, cerebrovascular syphilis, and meningovascular syphilis may also occur.

3. Tertiary Syphilis (Late-Stage Syphilis) This occurs two years after infection. Approximately 40% of untreated syphilis patients develop active late-stage syphilis, of which 15% develop benign syphilis, 10%–25% develop cardiovascular syphilis, and 10% develop neurosyphilis. Benign syphilis refers to syphilis affecting non-fatal tissues and organs, such as the skin, soft tissues, bones, cartilage, and testes.