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INTRODUCTION

The human treponematoses remain important health problems worldwide.1 Venereal syphilis, caused by Treponema pallidum subsp. pallidum, is a major public health challenge in both low and high-income settings whilst the three endemic (nonvenereal) endemic treponematoses remain significant problems in more focal regions of the world. Of the three endemic treponematoses (yaws, bejel, and pinta), yaws is the most prevalent globally.2

Yaws was previously widespread across the topics, but is now believed to be restricted to foci in West and Central Africa, South East Asia, and the Pacific). As with the other treponematoses, yaws is characterized by a multi-stage infection that predominantly affects the skin, bones, and cartilage.3 During the twentieth-century penicillin was the mainstay of treatment,4 but more recently azithromycin has been shown to be an effective therapy leading to renewed efforts to eradicate the disease worldwide.5

CAUSATIVE ORGANISM

Yaws is caused by Treponema pallidum subsp. pertenue, a gram-negative spirochete. T. pallidum subsp. pertenue is morphologically indistinguishable from T. pallidum subsp. pallidum and from the other endemic treponematoses.6 Sequencing of a limited number of treponemal strains has shown the sequence of T. pallidum subsp. pallidum and T. pallidum subsp. pertenue are more than 99.8% identical and there is some evidence of recombination between T. pallidum. subsp. pertenue and T. pallidum subsp. pallidum.7,8 The identified differences between the genomes are restricted to a small number of regions, which it is believed may contribute to difference in the pathogenicity between subspecies. More recently whole genome sequencing of Treponema directly from clinical samples has become possible9 and it is likely that these new techniques will provide considerable new data on the relationship between Treponema subspecies.

PATHOGENESIS

Our knowledge of the pathogenesis of treponemal infections has been predominantly derived from animal models. The causative organisms are acquired by transmission through breaches in the skin or mucous membranes.3 Soon after initial infection, the treponemes disseminate to lymph nodes where they undergo rapid multiplication. Host immune responses are responsible for most of the pathology that accompanies infection and this is mediated by both cellular and humoral immune responses. It is currently believed that there is no long-lasting acquired immunity to treponemal infections and that following successful treatment individuals are therefore at risk of reinfection.

EPIDEMIOLOGY

Yaws is restricted to warm and humid environments4 and is the most prevalent of the three endemic treponematoses. During the twentieth century, it was believed that as many as 50 million individuals were infected by yaws. Successful control efforts in Haiti prompted the World Health Organization (WHO) to consider a global eradication effort and in 1949, the World Health Assembly passed a resolution supporting efforts for the control and elimination of the endemic treponematoses, including yaws. Between 1952 and 1964, WHO and ...

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