Detection of the Treponema pallidum gene and variation of treponemal DNA load before and after therapy.

We explored a genetic detection method for Treponema pallidum (TP) in the peripheral blood of infected patients to compare the loads of treponemal DNA before and after therapy and to see if this new technique enabled assessment of therapeutic effect and detection of serum resistance. Polymerase chain reaction was used for a qualitative detection of TP DNA in peripheral blood and then a semiquantitative method was adopted to estimate the load of TP DNA in blood, both before and after treatment of syphilis. Among 30 untreated patients, three cases were TP DNA-positive. Among 42 treated patients with demonstrated serum resistance, three cases were TP DNA-positive. Five cases in which the rapid plasma reagin had become negative had no detectable TP DNA in their peripheral blood. The TP DNA load in blood after treatment was significantly lower than that before therapy. We conclude that the detection of TP DNA in peripheral blood of TP-infected patients is not yet sufficiently sensitive, but we observed that TP DNA load declines significantly after treatment.