Genital chancre sores are specific ulcerations found primarily on the genitals, anus, or mouth. These lesions are typically caused by bacteria transmitted through sexual contact, indicating a sexually transmitted infection (STI). Understanding the specific pathogen responsible for the sore is important because different bacteria cause different types of ulcers.
The Primary Cause: Syphilis
The classic chancre is most commonly caused by Syphilis, initiated by the bacterium Treponema pallidum. This corkscrew-shaped organism penetrates the skin or mucous membranes, often through tiny abrasions occurring during sexual activity. The appearance of the chancre marks the primary stage of the infection.
The chancre of primary Syphilis is characterized by being a single lesion that is firm, round, and has a clean, well-defined border. This firmness is known as induration, giving the sore a button-like consistency when touched. A distinguishing feature of the syphilitic chancre is that it is typically painless. If left untreated, this lesion will eventually heal on its own, but the infection will progress through the body to later, more damaging stages.
Other Bacterial Infections Leading to Sores
While Syphilis causes the classic chancre, other bacterial STIs also result in genital ulcerations sometimes referred to as “soft chancres.” Chancroid is one such infection, caused by the bacterium Haemophilus ducreyi. The sores resulting from this infection are distinct from Syphilis and are characterized by being painful and having soft, ragged edges.
Two other infections that can lead to genital sores are Lymphogranuloma Venereum (LGV) and Granuloma Inguinale (Donovanosis). LGV is caused by specific, invasive serovars of Chlamydia trachomatis (L1, L2, or L3), distinguishing it from the more common chlamydia infection. Donovanosis is caused by Klebsiella granulomatis, and it produces chronic, progressive ulcers in the genital region.
Routes of Transmission
The bacteria responsible for these chancre-causing infections are primarily passed from person to person through sexual contact. Transmission occurs when there is direct contact with the infectious sore, rash, or mucous membrane lesion of an infected individual. This contact typically happens during vaginal, anal, or oral sex.
The bacteria must enter the body to establish an infection, usually through minor cuts, tears, or abrasions in the skin or mucous membranes. The fluid that oozes from an open ulcer, such as a syphilitic chancre or a chancroid sore, contains a high concentration of the causative bacteria. Even non-penetrative skin-to-skin contact with an active lesion can be sufficient to transmit the infection.
Key Differences in Sore Appearance
The physical characteristics of the ulcers provide important clues that differentiate these various bacterial infections. The syphilitic chancre is defined by its deep, firm base and lack of tenderness, often appearing as a single, well-demarcated lesion. It rarely has any pus or discharge on its surface, which is why it is described as having a “clean” base.
In sharp contrast, the chancroid lesion is typically painful, has soft, undermined borders, and frequently possesses a purulent, yellow-gray base. Chancroid is also commonly associated with a painful swelling of the lymph nodes in the groin, which can form a mass called a bubo. The initial sore of LGV is small, transient, and often goes unnoticed because it is painless and heals quickly. Donovanosis ulcers are chronic and progressive, characterized by raised, beefy-red tissue that bleeds easily on contact.