Treponema pallidum strain-specific differences in neuroinvasion and clinical phenotype in a rabbit model.

Background: The relationship between neuroinvasion and other manifestations of syphilis and the infecting strain of Treponema pallidum is not known.
Methods: Six groups of 8 rabbits were intravenously infected with 1 x 108 organisms from 1 of 6 strains of T. pallidum. Rabbits were examined 2-3 times/week; blood and cerebrospinal fluid (CSF) were collected weekly and every 2 weeks, respectively, for 10-12 weeks. Degree of CSF pleocytosis and skin-lesion severity were estimated by the area under the white blood cell-versus-time and lesion-versus-time curves.
Results: Maximum serum Venereal Disease Research Laboratory test titers, time to maximum titer, degree of CSF pleocytosis, and severity of skin lesions differed significantly among infecting strains. Overall, T. pallidum was identified, by reverse-transcriptase polymerase chain reaction, in CSF from 13 (27.7%) of 47 rabbits and was never identified in CSF from rabbits infected with 1 of the strains. The time course of detection varied by infecting strain. Severity of skin lesions and of CSF pleocytosis were inversely correlated (P=.005).
Conclusions: There are particularly neuroinvasive T. pallidum strains, and the clinical phenotype of infection varies with infecting strain. This information could ultimately be used to identify patients at increased risk for neuroinvasion and, thus, at risk for neurosyphilis.