Three genera of spirochetes cause human infection: (1) Treponema, which causes syphilis and the nonvenereal treponematoses; (2) Borrelia, which causes Lyme disease and relapsing fever; and (3) Leptospira, which causes leptospirosis (Table 24–1).
TABLE 24–1Spirochetes of Medical Importance ||Download (.pdf) TABLE 24–1 Spirochetes of Medical Importance
|Species ||Disease ||Mode of Transmission ||Diagnosis ||Morphology ||Growth in Bacteriologic Media ||Treatment |
|Treponema pallidum ||Syphilis ||Intimate (sexual) contact; across the placenta ||Microscopy; serologic tests ||Thin, tight, spirals, seen by dark-field illumination, silver stain, or immunofluorescent stain ||– ||Penicillin G |
|Borrelia burgdorferi ||Lyme disease ||Tick bite ||Clinical observations; microscopy ||Large, loosely coiled; stain with Giemsa stain ||+ ||Doxycycline or amoxicillin for early stage; penicillin G for late stage |
|Borrelia recurrentis ||Relapsing fever ||Louse bite ||Clinical observations; microscopy ||Large, loosely coiled; stain with Giemsa stain ||+ ||Tetracycline |
|Leptospira interrogans ||Leptospirosis ||Food or drink contaminated by urine of infected animals (rats, dogs, pigs, cows) ||Serologic tests ||Thin, tight spirals, seen by dark-field illumination ||+ ||Penicillin G |
Spirochetes are thin-walled, flexible, spiral rods (Figure 24–1). They are motile through the undulation of axial filaments that lie under the outer sheath. Treponemes and leptospirae are so thin that they are seen only by dark-field microscopy, silver impregnation, or immunofluorescence. Borreliae are larger, accept Giemsa and other blood stains, and can be seen in the standard light microscope.
Treponema pallidum—dark-field microscopy. The coiled form of this spirochete is in the center of the field. (Used with permission from Dr. Schwartz, Centers for Disease Control and Prevention.)
Additional information regarding the clinical aspects of infections caused by the organisms in this chapter is provided in Part IX, entitled Infectious Diseases.
Treponema pallidum causes syphilis.
T. pallidum has not been grown on bacteriologic media or in cell culture. Nonpathogenic treponemes, which are part of the normal flora of human mucous membranes, can be cultured.
T. pallidum grows very slowly. The medical importance of that fact is that antibiotics must be present at an effective level for several weeks to kill the organisms and cure the disease (see “Treatment” section later). For example, benzathine penicillin is the form of penicillin used to treat primary and secondary syphilis because the penicillin is released very slowly from this depot preparation, and bactericidal concentrations are present for weeks after administration of the antibiotic.
The antigens of T. pallidum induce specific antibodies, which can be detected by immunofluorescence or hemagglutination tests in the clinical laboratory. They also induce nonspecific antibodies (reagin),1 which ...