Clinical Manifestations
Treponemes cause diverse clinical manifestations. In patients with acquired venereal syphilis, there is an initial genital tract lesion (primary stage) followed by disseminated lesions (secondary stage) and, in approximately one-third of untreated individuals, cardiovascular and neurologic problems (tertiary stage). Infection during pregnancy (congenital syphilis) may result in fetal death or birth defects. Yaws, pinta, and endemic syphilis, the nonvenereal treponematoses, are usually present as skin or mucous membrane lesions. Soft tissue and bone lesions also can occur with yaws and endemic syphilis.
Structure and Biology
Treponemes are helically coiled, corkscrew-shaped cells, 6 to 15 ?m long and 0.1 to 0.2 ?m wide. They have an outer membrane which surrounds the periplasmic flagella, a peptidoglycan-cytoplasmic membrane complex, and a protoplasmic cylinder. Multiplication is by binary transverse fission. Treponemes have not yet been cultured in vitro.
Classification and Antigenic Types
Classification of the pathogenic treponemes is based primarily upon the clinical manifestations of the respective diseases they cause. Treponema pallidum subsp pallidum causes venereal syphilis; T pallidum subsp pertenue causes yaws; T pallidum subsp endemicum causes endemic syphilis; and T carateum causes pinta. Venereal syphilis is transmitted by sexual contact; the other diseases are transmitted by close nonvenereal contact.
Pathogenesis
Treponemes are highly invasive pathogens which often disseminate relatively soon after inoculation. Evasion of host immune responses appears to be, at least in part, due to the unique structure of the treponemal outer membrane (i.e., its extremely low content of surface-exposed proteins). Although treponemes lack classical lipopolysaccharide (endotoxin), they possess abundant lipoproteins which induce inflammatory processes.
Host Defenses
Various studies suggest that both cellular and humoral processes contribute to host defenses against treponemal infection. Clearance of treponemes from local sites appears to be due to phagocytosis by macrophages.
Epidemiology
Humans are the only source of treponemal infection; there are no known nonhuman reservoirs. Venereal syphilis is distributed worldwide, and over the past several decades has become a significant public health problem in many underdeveloped countries. Infectivity rates correspond to the most sexually active age groups. FollowingCopyright © 1996
The University of Texas Medical Branch at Galveston