Syphilis is a serious infection caused by the bacterium Treponema pallidum. While most cases are transmitted through sexual activity, the infection can also be contracted through routes that do not involve penetrative intercourse. The disease often begins with a painless sore, called a chancre, which appears where the bacteria entered the body.
Transmission Through Direct Contact with Active Sores
The primary means of non-intercourse transmission is direct, skin-to-skin contact with an active syphilitic sore. The bacteria require moisture and warmth, and they enter a new host through minor cuts, abrasions, or intact mucous membranes. This contact is most likely to occur during intimate sexual activity, even without full penetration.
Chancres are highly infectious during the primary stage and can occur on the genitals, anus, rectum, lips, or in the mouth. Transmission can occur through deep, open-mouth kissing if one person has an active sore, allowing the bacteria to transfer. This is possible because the chancre is teeming with T. pallidum bacteria.
A less common scenario involves manual contact with an active lesion followed by touching one’s own mucous membranes. If an individual touches a moist rash in the secondary stage and then immediately touches their eye or mouth, there is a theoretical risk of self-inoculation. Transmission requires the bacteria to pass directly from the infected sore to a break in the skin or a mucosal surface of the uninfected person.
Congenital Syphilis
Another non-sexual route is vertical spread from a pregnant parent to their fetus, known as congenital syphilis. This occurs when Treponema pallidum bacteria cross the placental barrier and enter the fetal bloodstream. The risk of transmission is highest, ranging from 60 to 100%, during the parent’s primary and secondary stages of the disease.
Untreated Syphilis during pregnancy can have severe consequences, with adverse outcomes occurring in more than half of all cases. These outcomes include miscarriage, stillbirth, premature delivery, and neonatal death. Surviving babies may be born with complications such as bone inflammation, organ damage, or neurological issues.
The infection can be fatal to the fetus before a live birth can even occur. Routine prenatal screening and early treatment with penicillin can cure the infection in the parent and often prevent these severe outcomes for the fetus. Treatment is particularly effective when administered early in the pregnancy, ideally before the second trimester.
Addressing Common Misconceptions About Spread
The Treponema pallidum bacterium is fragile and cannot survive for long outside the human host. This biological limitation is why the infection cannot spread through casual, non-sexual interactions. The bacterium requires the moist, warm environment of the human body to remain viable.
It is not possible to contract Syphilis from inanimate objects such as toilet seats, doorknobs, swimming pools, or hot tubs. Sharing clothing, eating utensils, or bath towels does not transmit the infection. The infection cannot be passed through casual physical contact, such as hugging or shaking hands. Syphilis requires direct, sustained contact with an active, infectious sore for the bacteria to enter the body.