Enhanced molecular typing of treponema pallidum: geographical distribution of strain types and association with neurosyphilis

Abstract

Background: Strain typing is a tool for determining the diversity and epidemiology of infections.

Methods: Treponema pallidum DNA was isolated from 158 patients with syphilis from the United States, China, Ireland, and Madagascar and from 15 T. pallidum isolates. Six typing targets were assessed: (1) the number of 60‐bp repeats in the acidic repeat protein gene, (2) restriction fragment length polymorphism (RFLP) analysis of T. pallidum repeat (tpr) subfamily II genes, (3) RFLP analysis of the tprC gene, (4) determination of tprD allele in the tprD gene locus, (5) the presence of a 51‐bp insertion between tp0126 and tp0127, and (6) sequence analysis of an 84‐bp region of tp0548. The combination of targets 1 and 2 comprises the Centers for Disease Control and Prevention (CDC) T. pallidum subtyping method.

Results: Adding sequence analysis of tp0548 to the CDC method yielded the most discriminating typing system. Twenty‐five strain types were identified and designated as "CDC subtype/tp0548 sequence type." Type 14d/f was found in samples from 5 of 6 locations. In Seattle, Washington, strain types changed from 1999 through 2008 (P < .001). Twenty‐one (50%) of 42 patients infected with type 14d/f had neurosyphilis compared with 10 (24%) of 41 patients infected with any of the other types combined (P = .02).

Conclusion: We describe an enhanced T. pallidum strain typing system that shows biological and clinical relevance.

Figure 1

Typing groups determined by sequence of bp 131 to 215 in the tp0548 open reading frame.

Figure 2

Comparison of CDC subtypes to strain types as defined by addition of sequence analysis of tp0548 to the CDC method. Fourteen CDC subtypes could be divided into 24 strain types. Importantly, the 3 subtypes containing 14 arp repeats could be separated into 8 separate types using the enhanced typing scheme.

Figure 3

Strain types identified in six geographic regions. More than one strain type was seen in all locations, and Type 14d/f was identified in all sites other than Madagascar. Several strain types were seen in only a single location.

Figure 4

Strain types identified in each year from 1999 through 2008 in patients from Seattle, WA, showing introduction and loss of some strain types during that period. There was significant change in type over time (p<0.001).