<em>Treponema pallidum</em> Infection in the Wild Baboons of East Africa: Distribution and Genetic Characterization of the Strains Responsible

<div><p>It has been known for decades that wild baboons are naturally infected with <em>Treponema pallidum</em>, the bacterium that causes the diseases syphilis (subsp. <em>pallidum</em>), yaws (subsp. <em>pertenue</em>), and bejel (subsp. <em>endemicum</em>) in humans. Recently, a form of <em>T. pallidum</em> infection associated with severe genital lesions has been described in wild baboons at Lake Manyara National Park in Tanzania. In this study, we investigated ten additional sites in Tanzania and Kenya using a combination of macroscopic observation and serology, in order to determine whether the infection was present in each area. In addition, we obtained genetic sequence data from six polymorphic regions using <em>T. pallidum</em> strains collected from baboons at two different Tanzanian sites. We report that lesions consistent with <em>T. pallidum</em> infection were present at four of the five Tanzanian sites examined, and serology was used to confirm treponemal infection at three of these. By contrast, no signs of treponemal infection were observed at the six Kenyan sites, and serology indicated <em>T. pallidum</em> was present at only one of them. A survey of sexually mature baboons at Lake Manyara National Park in 2006 carried out as part of this study indicated that roughly ten percent displayed <em>T. pallidum</em>-associated lesions severe enough to cause major structural damage to the genitalia. Finally, we found that <em>T. pallidum</em> strains from Lake Manyara National Park and Serengeti National Park were genetically distinct, and a phylogeny suggested that baboon strains may have diverged prior to the clade containing human strains. We conclude that <em>T. pallidum</em> infection associated with genital lesions appears to be common in the wild baboons of the regions studied in Tanzania. Further study is needed to elucidate the infection's transmission mode, its associated morbidity and mortality, and the relationship between baboon and human strains.</p> </div

Sampling and site characteristics of baboon troops in which animals were tested for <i>T. pallidum</i>, including seroprevalence and the prevalence of outward signs of infection with <i>T. pallidum</i>.

a<p>Sample seroprevalence may be inflated at GSNP, LMNP, and SNP, as some baboons were purposively sampled in the serological survey. Three of eight animals in GSNP, seven of nineteen at LMNP, and five of twenty-five at SNP were included because they displayed anogenital lesions.</p>b<p>GSNP has a history of antibiotic treatment of affected individuals <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050882#pone.0050882-Wallis1" target="_blank">[11]</a>, which may affect prevalence of infection there.</p>c<p>The collection of biological samples was not permitted at this site.</p

A phylogeny demonstrates that <i>T. pallidum</i> strains infecting baboons in Serengeti National Park and Lake Manyara National Park are genetically distinct from one another.

<p>Phylogenies were constructed using both Maximum Parsimony and Maximum Likelihood methods to analyze 25 polymorphisms in six concatenated regions of the <i>Treponema</i> genome. The phylogenies were congruent and a Maximum Parsimony tree was chosen for display, with bootstrap support displayed at all nodes that received greater than 50% using both methods.</p