Introduction
Syphilis and yaws are caused by Treponema pallidum (TP )
ssp. pallidum (syphilis; TPA ) and ssp. pertenue(yaws; TPE ), respectively. While syphilis is a human disease with
several hundred-year long history, yaws is a disease of humans and
nonhuman primates (Majander et al., 2020; Beale et al., 2021). Studies
on modern TPA lineages controversially discuss a common ancestor
of all TPA strains in the 1700s (Arora et al., 2016). However,
the evolution of TPA , its closest relative TPE and the
genetically closely related lagomorph syphilis-causing bacteriumTreponema paraluisleporidarum ecovar Lepus (TP eL) in hares
and T. paraluisleporidarum ecovar Cuniculus (TP eC) in
rabbits remains elusive. Only a single complete genome of a
rabbit-infecting laboratory-maintained strain from the USA has been
whole-genome sequenced until today (Šmajs et al., 2011). Comparative
studies showed that this strain, TP eC strain Cuniculi A, has a
98.1% whole-genome identity to the human syphilis-causing TPAstrain Nichols (Šmajs et al., 2011; Pětrošová et al., 2013). Although
its genome is slightly smaller compared to that of the human infecting
syphilis bacterium there is a general genome synteny (Šmajs et al.,
2011). Yet, all information on genomic deletions, insertions or changes
that likely code for the lagomorph host specificity is derived from the
single published TP eC strain Cuniculi A genome (Strouhal et al.,
2007; Šmajs et al., 2011). Consequently, the basis for
human-pathogenicity cannot be identified unless more Treponemagenomes of lagomorph origin are analysed.
Our previous studies have demonstrated anti-Treponema antibodies
and the presence of the bacterium in several European brown hare
(Lepus europaeus ; EBH) populations (Nováková et al., 2019; Hisgen
et al., 2020, 2021). Serology and quantitative PCR were, however, unable
to distinguish infection with TP eL, TP eC or the
genetically closely related TP . We note here that the latter is
not known to infect wild lagomorphs, but rabbits are traditionally used
to cultivate human treponemes in vivo which highlights the ability forTP to adapt and survive in the lagomorph host (Lukehart and
Marra, 2007). In this study and prior to whole-genome sequencing, we
were interested in the molecular epidemiology and the genetic diversity
of treponemes infecting European lagomorphs. In the light of the
previously reported wide-spread infection in the wild lagomorph-host,
which argues for a well-established disease in European lagomorphs, we
hypothesised that hare infecting strains have a strain diversity as high
as the one seen in a comparative wild host-pathogen system – African
nonhuman primates infected with the sister-bacterium TPE (Chuma
et al., 2019). We predicted a geographic clustering of strains isolated
from structurally connected hare populations. We used the naturally
occurring Treponema infection in nonhuman primates as a direct
comparison since the infection in wild lagomorphs is equally not under
selection pressure from antibiotic treatment (Knauf et al., 2018) and
has multiple host species involved. Due to the high genetic similarity
of human and nonhuman primate infecting TP and hare and rabbit
infecting TP eL/C (98.1% genome identity; (Šmajs et al., 2011)),
we applied a multi-locus sequence typing system that was originally
designed for TPE infection in nonhuman primates (Chuma et al.,
2019).