Endemic treponematoses

1 - DEFINITION

Treponematoses are infections caused by the spirochetal organisms of the Treponema species which belong to the Spirochaetales class. These bacteria are the cause of both syphilis (Treponema pallidum ssp pallidum) and the so-called nonvenereal or endemic treponematoses (ET) consisting of bejel (or endemic syphilis, firjal) (T. pallidum spp endemicum), which is prevalent in the dry Sahel region of Africa, yaws (also known as pian, framboesia, parengi, paru and bouba) (T. pallidum spp pertenue), arising in humid tropical or equatorial regions worldwide, pinta (caraté, mal del pinto, puru-puru) (T.carateum), which is now extremely rare but still occurs in some areas of Central and South America. It is impossible to culture these different spirochetes in vitro or to distinguish between them morphologically. Furthermore, they develop, are diagnosed and treated in the same way.

Neither genomic nor paleoanthropological studies have been able to establish the origins of syphilis but it has been suggested that it involves a mutation of the pinta treponeme, spread by the conquistadors, into the bejel treponeme in dry regions. The venereal form of syphilis is then believed to have emerged in Europe and the Middle East after a second mutation, transmitted through sexual intercourse between adults.

ETs are mainly transmitted through close nonvenereal contact between children and sometimes between children and adults as a result of cramped, insanitary living conditions; while possible, venereal transmission is an exceptional occurrence. Although maternal-foetal transmission has been described in congenital syphilis and observed in ET animal models, it has not been reported in human cases of ET. The high incidence of the disease in children is believed to be a result of lesser immunity. The "clinical" prevalence of endemic treponematoses is inversely proportionate to that of venereal syphilis in any given population, irrespective of age, and is possibly the result of cross-protective immunity since these treponemes share many antigens. The upsurge in these infections observed in the period 1980-2000 (after they were virtually eradicated by the mass penicillin treatment campaigns of the 1950s and 60s) is still poorly understood but is probably related to lack of follow-up care, the failure to carry out a second campaign a few years after the first and the deterioration in living conditions as a result of poverty or conflict; there is no proof suggesting that the AIDS epidemic has played a role.