Assessment of the Kinetics ofTreponema pallidumDissemination into Blood and Tissues in Experimental Syphilis by Real-Time Quantitative PCR

Abstract

Little is known about the size and kinetics of treponemal burdens in blood and tissues during acquired or experimental syphilitic infection. We used real-time quantitative PCR to measure Treponema pallidum DNA levels in rabbits infected intratesticularly with the prototype Nichols strain. At the outset, we performed a series of in vitro blood spiking experiments to determine the effect of blood processing procedures on the distribution of treponemes in various blood components. T. pallidum DNA levels in plasma and whole blood were approximately 10-fold higher than those in serum and more than 200-fold greater than those in peripheral blood mononuclear cells (PBMCs). Ten rabbits were inoculated intratesticularly with doses of treponemes ranging from 4 ؋ 10 7 to 2 ؋ 10 8 organisms. In five rabbits, T. pallidum DNA levels were measured sequentially in serum, plasma, whole blood, and PBMCs until sacrifice at peak orchitis, at which time brain, kidney, liver, spleen, and testicles were harvested; blood and organs were also harvested at orchitis from the other five rabbits. T. pallidum DNA was detected in plasma within 24 h postinfection. Treponeme levels in whole blood and blood components increased significantly with the development of peak orchitis. Overall, levels in serum and PBMCs were lower than those in plasma and whole blood; this disparity was particularly marked at early time points. Significantly greater numbers of spirochetes were found in the spleen than in liver, kidney, or brain tissue at the time of sacrifice. Our findings highlight the remarkable capacity of T. pallidum to disseminate from the site of infection to blood and tissues, and they identify the spleen as a prime target for treponemal invasion.

Evaluation of a PCR Test for Detection of Treponema pallidum in Swabs and Blood

“…Our results suggest that the use of the whole-blood fraction would be more effective for the detection of T. pallidum in cases of secondary syphilis (38%), although the results for this fraction were not significantly different from those for the PBMC fraction (31%). Previous studies on rabbit models of syphilis infection reported that whole blood was the best sample for spirochete detection (36) and that T. pallidum was detected in 46% of the whole-blood samples obtained from 57 patients with secondary syphilis (9). This difference in sensitivity may result from the use of a different target gene (tpp47 versus polA) and the conditions in which whole blood was stored, as it has been shown that the freezing of samples may affect sensitivity (9).…”

Molecular Characterization of Syphilis in Patients in Canada: Azithromycin Resistance and Detection of Treponema pallidum DNA in Whole-Blood Samples versus Ulcerative Swabs

“…A third possible reason is the choice of specimen or timing of collection. Although the use of peripheral blood mononuclear cell fractions has been described to offer better detection than whole blood (12), this finding was not supported by observations in the rabbit infection model (29). Therefore, further studies with clinical specimens are required to clarify this issue.…”

Incidental Syphilis Diagnosed by Real-Time PCR Screening of Urine Samples

“…A synthetic positive control of 381 bp from the polA gene produced with a pUC57 plasmid was used, as well as a negative control for each run. Confirmation PCR targeting the flaA gene was performed as previously described (10). Over a period of 13 months, 1,706 samples from 1,409 patients were received, of which 887 (52%) were urine samples.…”