Strain diversity of Treponema pallidum subsp. pertenue suggests rare interspecies transmission in African nonhuman primates

Abstract

In our most recent study, we found that in Tanzania infection with Treponema pallidum (TP) subsp. pertenue (TPE) is present in four different monkey species. In order to gain information on the diversity and epidemiological spread of the infection in Tanzanian nonhuman primates (NHP), we identified two suitable candidate genes for multi-locus sequence typing (MLST). We demonstrate the functionality of the MLST system in invasively and non-invasively collected samples. While we were not able to demonstrate frequent interspecies transmission of TPE in Tanzanian monkeys, our results show a clustering of TPE strains according to geography and not host species, which is suggestive for rare transmission events between different NHP species. In addition to the geographic stability, we describe the relative temporal stability of the strains infecting NHPs and identified multi-strain infection. Differences between TPE strains of NHP and human origin are highlighted. Our results show that antibiotic resistance does not occur in Tanzanian TPE strains of NHP origin.

Figure 1

Median-joining network using 1,773 bp – long concatemer of TP0488 and TP0548 loci from 57 Tanzanian NHPs samples. The number of mutations, when >1, is given close to branches. Inferred allelic variants (median vectors) are shown as small black connecting circles. If contiguous, indels were considered as a single event only. The number of individuals, when >1, is shown inside the circles and are dependent on circle size. Species trait is given in the geometric form: circle = Papio anubis (n = 46); squares = Papio cynocephalus (n = 5); triangles = Chlorocebus pygerythrus (n = 5); hexagon = Cercopithecus mitis (n = 1). Sample location trait is given by the color code: blue = UG (n = 3); orange = TN (n = 1); brown = Ruaha National Park (n = 4); red = Lake Manyara National Park (n = 34); grey = Serengeti National Park (n = 7); green = Ngorongoro Conservation Area (n = 5); violet = Gombe National Park (n = 3).

Figure 2

Rooted ML tree based on the concatenated sequences used for MLST (TP0548 and TP0488). The tree is based on 1,773 nts and 1,000 bootstrap replicates. Bootstrap values from 80–100% are highlighted as light blue circles of respective size. NHP species and/or GenBank accession numbers of published strains are provided in parentheses following the name of the strain. In all cases were the species is not mentioned, sequences are from TP of human origin. Blue = subsp. pallidum, green = subsp. pertenue, red = subsp. endemicum. The pathogen causing rabbit syphilis, Treponema paraluisleporidarum ecovar Cuniculus strain Cuniculi A, is used as an outgroup. The bar refers to substitutions per site.

Figure 3

Temporal strain composition for samples collected from olive baboons at Lake Manyara National Park. The different colors indicate different genotypes. Sampling of olive baboons at LMNP was conducted in 2007 and 2015. The strain “E” (light green; e.g., 4LMF8160815) was the dominating strain in 2007 and was still present in baboons sampled eight years later (2015).