Syphilis is a sexually-transmitted disease (STD) caused by the bacteria Treponema pallidum. It is one of the more common STDs, with over 36,000 cases per year reported in the United States. It is primarily transmitted through sexual contact and contact with syphilitic ulcers, but it is possible to transmit syphilis through saliva during certain stages of the disease. When ulcers containing the bacteria form in the mouth, the disease can be spread through kissing or through oral-genital contact.
The transmission of syphilis is most common through genital sexual contact. During first-stage syphilis, painless ulcers known as chancres form around the area of primary contact with the bacteria. These ulcers are largely painless and generally occur around the genitals. If pallidum bacteria come into contact with the soft tissues inside the mouth, chancres may form on the lips, tongue, or the interior of the mouth. During this stage, the transmission of syphilis through saliva is possible, as the chancres are full of infectious bacteria. If saliva containing pallidum bacteria comes into contact with the mucous tissues or damaged skin of another person, infection may occur.
After a few weeks, syphilitic chancres typically disappear on their own. They are replaced 10 to 90 days later with a painless rash that commonly occurs on the hands and feet. The rash, like the chancres, is capable of spreading pallidum bacteria to those who come into contact with it, and oral contact with the rash may result in briefly infectious saliva. Ulcers may also appear on the inside of the cheeks and lips, creating another possible vector of the transmission of syphilis through saliva.
The bacteria that causes syphilis cannot survive for long outside the human body. While direct contact with the saliva of an infected person may lead to infection, indirect contact is not likely to be infectious. Also, although the blood of a syphilitic person can remain infectious for around four years, the potential to spread the infection through saliva is limited solely to the early stages of the disease. Almost all cases of syphilitic transmission occur during the first year of the disease, with the potential for infection dropping off almost entirely after four years.
Syphilis can be successfully treated with antibiotics if it is detected early. The treatment also leads to the disappearance of chancres, rash, and mouth ulcers, and this closes off most of the possible vectors of infection of syphilis through saliva. Early treatment is recommended, both to halt the spread of the disease to others and to avoid the potentially serious affects of late-stage syphilis.