An experimental model of early central nervous system syphilis.

Although up to 40% of patients with early syphilis have evidence of central nervous system (CNS) invasion by Treponema pallidum, the pathogenesis of CNS syphilis is not understood. A rabbit model that mimics early CNS involvement in humans was developed and characterized. Mild cerebrospinal fluid pleocytosis was evident 2 weeks after intracisternal inoculation of T. pallidum and peaked at 9 weeks. The VDRL test in cerebrospinal fluid was reactive in 24% of animals, most commonly at 9 weeks after infection. T. pallidum could be isolated from the CNS of animals infected for 4, 6, or 9 weeks but not from animals infected for 12 or 20 weeks. Clinically, 6% of animals developed uveitis, similar to the frequency in patients with secondary syphilis. Thus, this model of meningeal and ocular syphilis seems to be analogous to the early CNS infection in humans and can be used for studies of pathogenesis and treatment.