Syphilis

Syphilis, a chronic systemic infection caused by Treponema pallidum subspecies pallidum, is usually sexually transmitted and is characterized by episodes of active disease interrupted by periods of latency. After an incubation period averaging 2 to 6 weeks, a primary lesion appears, often associated with regional lymphadenopathy. A secondary bacteremic stage, associated with generalized mucocutaneous lesions and generalized lymphadenopathy, is followed by a latent period of subclinical infection lasting many years. In about one-third of untreated cases, the tertiary stage is characterized by progressive destructive mucocutaneous, musculoskeletal, or parenchymal lesions; aortitis; or symptomatic central nervous system disease.

Cause of Syphilis

The genus Treponema includes T. pallidum subspecies pallidum, which causes venereal syphilis. Recent studies have identified molecular signatures that can differentiate T. pallidum subspecies pallidum from the other pathogenic T. pallidum subspecies by culture-independent, polymerase chain reaction (PCR)-based methods. The only known natural host for T. pallidum is the human. T. pallidum can infect many mammals, but only humans, higher apes, and a few laboratory animals regularly develop syphilitic lesions. Virulent strains of T. pallidum are grown and maintained in rabbits.

Approximately one of every two individuals named as sexual contacts of persons with infectious syphilis becomes infected. Many sexual contacts will already have developed manifestations of syphilis when they are first seen, and about 30% of apparently uninfected contacts who are examined within 30 days of exposure actually have incubating infection and will later develop infectious syphilis if not treated.

Late Syphilis The slowly progressive inflammatory disease leading to tertiary manifestations begins early during the pathogenesis of syphilis, although these manifestations may not become clinically apparent for years. Early syphilitic aortitis becomes evident soon after secondary lesions subside, and patients who develop CSF abnormalities during the early stages of syphilis appear to be at highest risk of late neurologic complications.

Treatment of Syphilis

Serum levels of penicillin G of ³0.03 ug/mL for at least 7 days are considered necessary for the cure of early syphilis. Recurrence rates for a given regimen increase as infection progresses from incubating to seronegative primary to seropositive primary to secondary to late syphilis. Therefore, it is probable, but unproven, that a longer duration of therapy is required to effect cure as the infection progresses. For these reasons, some authorities use more prolonged penicillin therapy than that recommended by the U.S. Public Health Service when treating secondary, latent, or late syphilis.