Molecular Detection and Typing of Treponema pallidum in Non-Ocular Samples from Patients with Ocular Syphilis

Ocular syphilis is a rare but potentially sight-threatening manifestation of infection with the spirochete Treponema pallidum subspecies pallidum. Molecular strain typing of clinical specimens obtained from patients with syphilis can provide useful epidemiological and clinical information. In this study, we assess the utility of non-ocular clinical samples in strain typing for patients with diagnosed ocular syphilis.

We collected samples of excess blood, serum, and cerebrospinal fluid (CSF) from 6 patients with ocular syphilis treated in 2013-2016. DNA was extracted, purified, and then analyzed using an enhanced molecular typing method including sequence analysis of tp0548, number of repeats in the arp gene, and restriction fragment length polymorphism of the tpr gene.

Molecular strain typing based on tp0548 gene sequence analysis revealed two cases of type F and two cases of type G in 3 of 6 (50%) cases with CSF samples, 1 of which was obtained after starting antibiotics. In a patient with 2 distinct episodes, the same tp0548 type (type G) was identified in both episodes using different sample types (CSF, whole blood). Serum samples were available in 6 cases, but none were successfully typed with any of the methods. Amplification of the tpr and arp genes was unsuccessful in all cases. Overall, strain types were identified in 4 of the 7 episodes.

Treponema pallidum strain types F and G were detected in CSF or whole blood in 4 of 7 episodes in this series. We demonstrate moderate sensitivity of strain typing in ocular syphilis using non-ocular clinical specimens.