IDENTIFICATION OF PERSISTENT INFECTION IN EXPERIMENTAL SYPHILIS BY PCR

The studies described herein were designed to evaluate the usefulness of the PCR in detecting persistent syphilitic infection. Three groups of animals were used: a nonimmune group infected with Treponema pallid um (NI/TP), a nonimmune group injected with heat-killed treponemes (NI /HKTP), and an immune and reinfected group (I/TP), All animals were in oculated with similar numbers of organisms distributed at 10 sites on the clipped back and in both testes, The persistence of the treponemes was examined by PCR and the rabbit infectivity test (RIT). The kineti c studies and statistical analysis of their results demonstrated that the rate of bacterial clearance from the NI/TP group was very low and incomplete at 4 months after infection. It was significantly different from those of both the NI/HKTP (P < 0.001) and I/TP (P < 0.05) groups . No statistically significant differences in treponemal elimination w ere found between the NI/HKTP and UTP groups. PCR can detect the DNA o f dead organisms, but the latter are eliminated by the host relatively quickly (15 to 30 days) as compared to elimination of live treponemes (>120 days), PCR results correlated well with RIT results. These data suggest that PCR-positive specimens obtained from an untreated patien t(s) or collected weeks after treatment indicate persistent infection. They also show that the process of elimination of T. pallidum from pr imary sites of infection is prolonged and incomplete.