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Infections with treponemes and rickettsial organisms can produce a broad array of clinical manifestations, ranging from seemingly trivial viral-like illnesses to fulminant progressive disease. Recognition of these infections often requires correlation of a comprehensive travel and medical history with a detailed knowledge of the clinical and pathologic features of each.

*The opinions expressed herein are those of the author(s) and are not necessarily representative of those of the Uniformed Services University of the Health Sciences (USUHS), the Department of Defense (DOD); or, the United States Army, Navy, or Air Force.


Treponemal diseases are caused by bacteria of the family Spirochaetaceae. The pathogenic treponemes measure 6 to 20 by 0.10 to 0.18 µm, are coiled with regular periodicity, and react with silver stains in dark-field and biopsy material (Fig. 20-1).1 The nonvenereal treponematoses are endemic syphilis, yaws, and pinta.2 The use of polymerase chain reaction (PCR) methodologies and restriction polymorphism analysis had allowed the identification of at least 27 distinct strains of pathogenic treponemal species by 1997; a single genetic signature in the 59 and 39 flanking regions of the 15-kDa lipoprotein gene tpp15 distinguished the venereal and nonvenereal treponematoses in one study.2 Other studies have shown an 87% sequence homology of an open reading frame gene (tprJ) between the treponemes causing syphilis and yaws.3 The evidence suggests that these organisms have evolved from a common ancestor to cause different diseases in the modern era.4 In addition to certain highly conserved domains, ample size and sequence heterogeneity are demonstrable in other treponeme genes such as those that control expression of the TprK antigen, a target of opsonizing antibodies and thus important to host immune protection; such variances may play a role in evasion of the host response.5 Recently, the role of oral treponemes in the causation of periodontitis has been explored.6-8


Primary syphilitic chancre. A silver stain (Steiner) reveals elongated coiled spirochetes from 8 to 12 µm in length in a perivascular distribution.

Venereal syphilis

Clinical Features

Venereal syphilis, caused by Treponema pallidum, was a significant cause of morbidity and mortality in the early twentieth century, although its incidence in the developed world has so diminished that many physicians are now unfamiliar with its manifestations.1 The incidence of acquired syphilis increased in the 1980s to 20 per 100,000 in North America.1 New diagnoses of syphilis increased eightfold in the United Kingdom between 1997 and 2002.9 By 2003, more than 60% of all reported cases of syphilis were believed to occur in men who have had sex with men.10

Spread of T. pallidum usually occurs by contact between an infectious lesion and disrupted ...

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