Genetic diversity of Treponema paraluisleporidarum isolates in European lagomorphs

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The bacterium Treponema paraluisleporidarum causes syphilis in Lagomorphs. In a set of 1,095 samples from four species – European brown hare (Lepus europaeus), mountain hare (Lepus timidus), Corsican hare (Lepus corsicanus) and European rabbit (Oryctolagus cuniculus) – we genotyped the strains that infect wild lagomorphs. Samples originate from Sweden, the Netherlands, the United Kingdom, Germany, the Czech Republic and Italy. The phylogenetic analyses of two informative gene targets (tp0488 and tp0548) showed high genetic diversity among the lagomorph-infecting treponemes. More specifically, we found a high number of nucleotide variants and various short repeat units in the tp0548 locus which have not been described for human syphilis and primate yaws causing Treponema pallidum. While the functional aspect of these short repeat units remains subject to ongoing investigations, it likely enables the pathogen to better survive in its lagomorph host. Our data did not support any geographic clustering which is equally reflected in the host population genetics as shown by mitochondrial genome data corresponding to the sampled lagomorph populations. This is unexpected and in contrast with what has been shown for nonhuman primate infection with T. pallidum. In the future, the combination of multi-locus sequence typing and WGS from modern and ancient samples from a wide geographic range and multiple lagomorph species will contribute to a better understanding of the epidemiology and evolutionary path of lagomorph-infecting treponemes. In conclusion, our current study demonstrates a high genetic variation of the syphilis-causing pathogen in a higher number of positively PCR-tested European lagomorphs (n=496/1095).

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