Primary syphilis is the first stage of a three-stage sexually transmitted bacterial infection. It generally develops within a few weeks of being exposed to and infected by the bacteria Treponema pallidum. The main symptom of primary syphilis is a skin ulcer. Diagnosis can involve testing fluid taken from this sore and/or special blood tests. While primary syphilis usually goes away on its own, the underlying infection typically requires treatment with antibiotics to help prevent possible complications, including the progression to the latter stages of syphilis.
The bacteria that causes primary syphilis is known as Treponema pallidum. It usually enters the body through broken skin, such as a cut or other irritation, or mucous membranes, such as those found in the mouth and genitals. One of the most common ways the bacteria is spread is via sexual contact, which is why syphilis is generally referred to as a sexually transmitted disease.
About three to four weeks after first being infected with Treponema pallidum, the main symptom of primary syphilis typically develops. This primary sign is a single ulcerated spot of skin, called a chancre. It is generally painless and appears at the site where the bacteria entered the body. Given that syphilis is often spread through sexual contact, many chancres are found on or around the genitals, anus or lips, or in the mouth. In addition to the chancre, primary syphilis may also cause swelling of the lymph nodes, particularly in areas closest to where the chancre develops.
To diagnose primary syphilis, a sample of fluid from the chancre may be taken. Chancres usually produce a clear fluid that’s filled with the bacteria, which can often be seen when a small sample of the fluid is placed under a dark-field microscope. In some cases, special blood tests may used in place of or in addition to chancre fluid testing.
A primary syphilis chancre normally resolves on its own within one to two months after first appearing, but this does not signal the end of the underlying infection. Without treatment, a person can still pass the infection on to others, and will usually go on to develop secondary and then tertiary syphilis, which can be deadly. Treating primary syphilis can help cure the infection, helping to prevent further transmission and disease progression. It may also help the chancre heal more quickly.
The main treatment for primary syphilis is antibiotics. In general, a penicillin-based antibiotic is the preferred treatment. For people who are allergic to penicillin or can’t take it for some other reason, other antibiotics, such as cephalosporins, may be used. The length of treatment may vary depending on the medication used and an individual’s response to treatment. In general, a person has to have blood tests done at regular intervals to monitor treatment and make sure the infection is fully cured; until that time, health-care providers generally recommend using safer sex practices to avoid passing on the disease.
