Author: Learning in 10

Welcome to Learning in Ten series. I'm Dr. Jenny Low, infectious diseases consultant with the Department of Infectious Diseases at Singapore General Hospital. We will be touching on the subject of primary syphilis today.

Upon completion of this presentation, you will be able to describe the transmission and pathogenesis of Treponema pallidum, discuss the clinical manifestations of primary syphilis, identify common methods used in the diagnosis of primary syphilis, list the common treatment regimens for primary syphilis, and appreciate the importance of prevention counseling messages for patients with primary syphilis. The topic online is as follows, transmission and pathogenesis, signs and symptoms of primary syphilis, laboratory diagnosis of primary syphilis, treatment of primary syphilis, and finally prevention. Syphilis is transmitted via sexual and vertical routes. It is most contagious to sex partners during the primary and secondary stages.

The etiologic agent is Treponema pallidum, subspecies pallidum. It is a corkscrew-shaped, motile microaerophilic bacterium. It is important to remember that the bacterium cannot be cultured in vitro and cannot be viewed by normal light microscopy. It can only be visualized via specialized darkfield microscopy. Treponema pallidum enters the body via skin and mucous membranes through abrasions during sexual contact or via the placenta from mother to fetus during pregnancy. It then disseminates via the lymphatic system to regional lymph nodes, and then throughout the body via the bloodstream.

Invasion of the central nervous system can occur during any stage of syphilis. At the site of inoculation, a primary lesion called a chancre develops after infection. The Shinto chancre progress from a macule to a papule and finally to an ulcer. It is classically described as painless indurated ulcer with a clean base. This lesion is highly infectious.


Over a course of one to six weeks, the lesion heals spontaneously, even without any treatment. Occasionally, multiple lesions may be present. Regional painless rubbery bilateral lymphadenopathy may be present. Laboratory diagnosis of primary syphilis depends on identification of Treponema pallidum on lesions via darkfield microscopy or direct fluorescent antibody testing. Serologic tests.

Both nontreponemal tests and treponemal tests may not be positive in the primary stage of the infection. On the darkfield microscopy, one looks for Treponema pallidum morphology and motility. The advantage is a definite, immediate diagnosis. There are several disadvantages.

The test requires specialized equipment and an experienced microscopist. There can be possible confusion with other pathogenic and nonpathogenic spirochetes, and the test must be performed immediately. The test is generally not recommended for oral lesions, and there's a possibility of false negative on this test. On direct fluorescent antibody, one looks for Treponema pallidum in direct lesions smear by immunofluorescence. The advantages are that the test is commercially available, and it compares favorably with darkfield microscopy. The disadvantage for this test is that there is a turnaround time of one to two days. Therapy for primary syphilis is benzathine penicillin G, 2.4 million units intramuscularly in a single dose.

If the patient is allergic to penicillin, doxycycline 100 milligrams orally twice daily for 14 days, or tetracycline 500 milligrams orally four times daily for 14 days are the alternatives. Of note, penicillin allergic patients with syphilis and HIV whose compliance can not be ensured should be desensitized and treated with penicillin. All patients who have syphilis should be tested for HIV infection. And consider screening patients with syphilis for other STDs based on risks. Patients should receive counseling and education on the nature of the disease, its transmission, the treatment and followup required, as well as risk reduction. Sex partners of syphilis patients should be examined and have a serology test performed and therapy instituted accordingly. All pregnant women should have at least one screening test done at first prenatal visit. Screening of other at risk population depends on local prevalence and patients' risk behavior.

In summary, syphilis is transmitted sexually or via trans-placental route. Primary syphilis is highly contagious. Treponema pallidum can not be cultured. Identification is via direct visualization of the organisms on darkfield microscopy commonly. Treatment of syphilis is with a single dose of benzathine penicillin, or doxycycline or tetracycline. Patient counseling, screening of partners, and routine screening of pregnant women are important public health measures to reduce disease prevalence and transmission in the population.

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Welcome to Learning in Ten series. I'm Dr. Jenny Low, infectious diseases consultant with the Department of Infectious Diseases at Singapore General Hospital. We will be touching…

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