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Introduction to Sexually Transmitted Diseases




Overview of the Etiologic Agent

Peak rates of syphilis in the United States occurred during the 1940s. Discovery of and subsequent treatment with penicillin therapy, along with public health programs, account for the dramatic decrease of syphilis among the U.S. population seen today. Still, syphilis is a major sexually transmitted disease (STD) and outbreaks of the disease have occurred in recent years. There were 52,995 cases of syphilis reported in 1996.

The incidence of disease is greatest in rural and urban areas of the South in the United States. The disease is also disproportionately distributed among the poor, minorities, and individuals who have multiple partners.

Syphilis is caused by the organism Treponema pallidum, a member of the family Spirochaetaceae. The organism is a tightly coiled, corkscrew-shaped bacterium. It cannot be cultured in vitro, and can only be viewed under darkfield or electron microscopy. The organism is too thin to be seen under light microscopy.


Transmission of the organism occurs by sexual contact. Thirty to forty percent of persons exposed to an infected person will acquire the bacterium. T. pallidum can also be transmitted via kissing, blood transfusion, or from a mother to her fetus through the placenta. The bacterium thus enters the body through abrasions in the skin or mucous membranes. The incubation period of syphilis is between 9 and 90 days, with an average of 21 days.

Signs, Symptoms and Treatment

There are four stages of an infection with T. pallidum.

The first stage of the disease, called primary syphilis, occurs when the microorganisms infect their entry site, activate the immune system, and cause a lesion. This lesion, called a chancre, begins looking like a pimple but later evolves into an indurated ulcer that has smooth and firm borders. A significant feature of the chancre is that it is painless. If the chancre occurs in a spot that is difficult to see, like the vagina, cervix or rectum, the infected person may not notice it. The vast majority of the infected will experience one single chancre, but multiple chancres can occur. The lesion goes away in 1 to 6 weeks without any medical treatment, and does not produce a scar. During primary syphilis a person may also have swollen lymph nodes.

Testing for syphilis usually involves a blood test that detects antibodies against the bacterium, or microscopic examination of samples from ulcers.

The second stage, secondary syphilis, occurs 2 to 8 weeks after the chancre appears. Secondary syphilis produces different symptoms in different people, but common symptoms include fever, fatigue, headache, sore throat and body aches. There is commonly a rash, which looks different depending on the person, but is present all over the body including on the palms of the hands and soles of the feet. There may also be an enlargement of the liver and spleen detectable on physical exam, as well as swollen lymph nodes, oral mucous patches, and hair loss. Like the chancre, these symptoms resolve spontaneously after 2 to 10 weeks without treatment.

A person is most infectious during the first and second stages of syphilis.

The third stage of syphilis, called latent syphilis, is divided into two parts, early and late. A person is said to have early latent syphilis when a blood test for syphilis is positive for the antibodies to T. pallidum but he or she does not have any symptoms of the disease. Early latent syphilis is diagnosed when the person is thought to have been infected in the past year. In early latent syphilis, the person can still pass on the infection to partners. Persons in early latent syphilis may also experience a recurrence of any of the symptoms of primary or secondary syphilis, though this is rare. Late latent syphilis is diagnosed when a person has a positive blood test, does not have symptoms of the disease, and is thought to have had the infection longer than one year. The late latent stage of syphilis can last 2 to 50 years.

The final stage of syphilis is called tertiary syphilis. It occurs when cases of syphilis go untreated, and is classified as gummatous, cardiovascular or neurosyphilis depending on which part of the body is affected.

Tertiary syphilis occurs years after the initial infection, and varies per person. Gummatous syphilis describes granulomatous lesions that occur in soft tissue and in the viscera as part of an immune response to T. pallidum. They may occur on the skin, in the mouth or throat, in the gastrointestinal tract or liver. Cardiovascular syphilis is rare, and is diagnosed when damage to the heart vessels occurs as a result of T. pallidum infection. Neurosyphilis is the manifestation of prolonged T. pallidum infection in the central nervous system. Symptoms of neurosyphilis present in a variety of ways in different patients, and may mimic other diseases, making the diagnosis difficult. Some people have no symptoms of neurosyphilis; others may have meningitis, optic neuritis, deafness, or a variety of other symptoms.

Treatment for all stages of syphilis is with antibiotics.

Special attention needs to be paid to pregnant women who test positive for syphilis, as there are high rates of transmission from mother to fetus, particularly when the woman has first or second stage syphilis.

Untreated syphilis during pregnancy can cause premature labor or stillbirth. Infants who are born infected with T. pallidum usually become sick by the third month of life. Manifestations of congenital syphilis include meningitis, anemia, and deafness, among others.

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