Treponema pallidum is the microaerophilic spirochete that causes syphilis, a chronic systemic venereal disease with multiple clinical presentations (the great imitator).
T. pallidum is a very small, spiral bacterium (spirochete) whose form and corkscrew rotation motility can be observed only by dark-field microscopy. The reproductive time is estimated to be 30 to 33 hours, in contrast to most bacteria, which replicate every 30 minutes.
Serum levels of antibiotics must therefore persist for at least 7 to 10 days to expose all replicating organisms.
The Gram stain cannot be used, and the bacteria can be grown only will sophisticated tissue culture techniques.
Syphilis is transmitted in 2 ways, either from intimate contact with infectious lesions (most common sexually) or blood transfusions (blood collected during early syphilis), or it is transmitted transplacentally from an infected mother to her fetus.
Therefore there are 2 distinct forms of syphilis: acquired and congenital.
Acquired syphilis is characterized by episodes of active disease (primary, secondary, tertiary stages) interrupted by periods of latency (latent syphilis).
In acquired syphilis, the organism rapidly penetrates intact mucous membranes or microscopic dermal abrasions and, within a few hours, enters the lymphatics and blood to produce systemic infection.
The central nervous system is invaded early in the infection; during the secondary stage, examinations demonstrate that more than 30% of patients have abnormal findings in the cerebrospinal fluid (CSF).
During the first 5-10 years after infection, the disease principally involves the meninges and blood vessels, resulting in meningovascular neurosyphilis. Later, the parenchyma of the brain and spinal cord are damaged, resulting in parenchymatous neurosyphilis.