A51.1

Clinical Causes: Primary anal syphilis is caused by sexual contact with an infected person, typically during anal intercourse. The bacterium Treponema pallidum is transmitted through direct contact with a syphilitic sore, which may be present in or around the anal region. Transmission may occur even if the infected individual shows no symptoms, as the bacteria can be present in secretions. In some cases, vertical transmission from mother to baby can also occur, though this is more pertinent to congenital syphilis. Poor sexual health practices and lack of protective measures can increase the risk of infection.

Key Symptoms: Appearance of a painless ulcer or sore in or around the anus. The sore typically has a clean base and firm, raised edges; it may be covered with a gray or white exudate. Swelling or enlarged lymph nodes near the anal region. In some cases, there may be no pain or discomfort, which can delay detection. Rarely, additional symptoms such as itching or irritation may occur. The sore typically lasts for a few weeks and heals on its own, but the infection persists if untreated, progressing to secondary syphilis.

Diagnosis Path: Physical examination of the anal area to look for characteristic ulcers or sores. Serologic blood tests to detect syphilis antibodies, such as the Rapid Plasma Reagin (RPR) or Treponemal pallidum antibody tests. Microscopic examination of lesion exudates under dark-field microscopy or direct fluorescent antibody tests to identify Treponema pallidum. Biopsy of the sore may be performed if needed, with histological examination to support diagnosis.

Treatment Protocols: Intramuscular injection of penicillin, which remains the most effective treatment. For those allergic to penicillin, alternative antibiotics such as doxycycline or tetracycline may be prescribed. It is important to follow the full course of treatment prescribed by a healthcare provider. Patients should abstain from sexual contact until the infection is fully treated and sores have healed. Follow-up blood tests are recommended to ensure the infection has been cured.