The Treponematoses

The members of genus Treponeme, family Trepone-mataceae, and order Spirochaetales consist of Treponeme pallidum (first described in 1905), which causes syphilis and nonvenereal syphilis; Treponeme per-tenue (first described in 1905), which is responsible for yaws; and Treponeme carateum (first described in 1938), which produces pinta. Or at least this is the way that most medical texts would have it. It may be, however, that the three pathogens in question are actually only one, for although they produce different pathological processes, the pathogens themselves are virtually indistinguishable under the microscope, and the diseases they cause respond to the same treatment. The origin of this infamous family and the relationship of its members to one another have been topics of considerable and very interesting debate since the 1970s, largely because such questions bear directly on the centuries-old debate of whether the Americans bestowed syphilis on the rest of the world.

Many agree that the treponemes probably evolved from microorganisms that originally parasitized decaying organic matter, and which later - perhaps hundreds of thousands of years ago - came to specialize in human hosts, but probably only after first parasitizing another animal host (Wood 1978). There is little disagreement that the first treponemes to parasitize humans did so by entering their bodies through traumatized skin and were subsequently passed on to other humans by skin-to-skin transmission. Real disagreement begins, however, over questions of where the first humans were infected, and the identity of the disease they were infected with.

E. H. Hudson (1958) has argued that the first of the treponemal infections was yaws and that it probably emerged in Central Africa where it quickly became endemic. Then, about 100,000 years ago, it accompanied migrating humans from Africa to spread around the globe. C. J. Hackett (1963), on the other hand, portrays pinta as the first treponemal disease, arising only about 20,000 years ago in Eurasia to spread throughout the rest of the world.

At issue here are two very different concepts of treponematosis. Hudson feels that the distinctions among the treponematoses - T. pallidum, T. perte-nue, and T. carateum - are artificial. In this so-called unitarian view, all of the human treponematoses actually constitute a single disease, but one that has different manifestations depending on cli mate and culture. Hackett, however, argues that the distinctions are very real - the consequence of mutations of the treponemal strains themselves. T. A. Cockburn (1961) has shown along Darwinian lines how human geographic isolation, especially after the Ice Age, could have led to treponemal speciation. Similarly, Don Broth well (1981) has also speculated on the evolution of the treponemes and suggests that there may have been six lines of Treponema, which have undergone separate microevolutionary development to reach the four in existence today.

Historically, yaws has been prevalent in the hot and moist regions of Asia and Africa where little in the way of clothing is worn, facilitating transmission from skin to skin. By contrast, nonvenereal syphilis has flourished in hot but dry regions, where it spreads mostly from mouth to mouth. Both of these illnesses are normally rural, fostered by unsanitary living conditions, and are usually endemic and thus diseases of children. Venereal syphilis, on the other hand, is a disease of adults, seems to have first become manifest in the urban areas of temperate climates, and has been portrayed by Hudson, Cockburn, and others as a consequence of improving hygienic conditions. Put succinctly, in colder climates where people were better clothed and washed, the treponemas were denied their established patterns of skin-to-skin or mouth-to-mouth transmission among youngsters. As a consequence, persons reached sexual maturity without exposure to them, and sexual intercourse became one more means of transmission for the treponemas, particularly in urban areas where sexual promiscuity and prostitution were common (Hudson 1958).

The historical gradation of treponemal infections from the yaws of warm, moist Africa south of the Sahara, through the nonvenereal syphilis in hot and dry North Africa, to venereal syphilis in a cooler and urbanizing Europe, has constituted a compelling geographic model for both Hudson and Hackett and their followers. They point out, nonetheless, that yaws, and both nonvenereal and venereal syphilis, may all be present in a relatively small geographic area, with yaws and perhaps nonvenereal syphilis dominating the rural area surrounding a city, which harbors syphilis. Moreover, both views hold that venereal syphilis was present in Eurasia long before the voyages of Columbus, but its symptoms were lumped with those other disfiguring illnesses including yaws and nonvenereal syphilis, usually under the rubric of leprosy.

Needless to say, this challenge to the long-held notion that syphilis was introduced from the Ameri cas has encountered some heavy opposition (Dennie 1962; Crosby 1969, 1972). Yet we know that pinta was present in the Americas when Columbus arrived, and both the unitarian and the mutation hypotheses accommodate the notion that other treponemal diseases could have developed there as well. In fact, Brothwell (1981) has argued that Asia was probably the cradle for the evolution of the treponemes pathogenic to humans, and that they diffused from there to the Americas via migrants across the Bering Straits landbridge to the New World, as well as throughout the Old World. In other words, it is conceivable that all the pathogenic human treponemes were present in each of the major land masses of the globe by 1492. Yet Hudson (1964) believes that endemic syphilis and yaws reached the Americans via the slave trade and there evolved into syphilis; Francisco Guerra (1978) holds that all four treponemal infections were present in the New World, but only endemic and venereal syphilis resided in the Old World until yaws, not syphilis, was imported from the Americas; whereas Corinne Wood (1978), after reviewing the arguments and evidence, finds the Columbian hypothesis for the origin of syphilis the most plausible.

Much of the evidence upon which this last conclusion is based is skeletal in nature, embracing both negative and positive findings. Most of the negative findings have to do with the Old World, where it turns out that those buried in leper cemeteries would seem to have been mostly lepers and not syphi-litics, as those who placed syphilis in Europe prior to the Columbian voyages felt would be the case. Moreover, there is (at least thus far) a dearth of evidence in Old World skeletal remains that would testify to the presence of syphilis in Eurasia prior to 1493, although the presence of yaws and endemic syphilis has been occasionally reported.

In the New World, by contrast, there is a great deal of positive skeletal evidence of pre-Columbian treponematosis. This evidence is not, however, of pinta (spotted), which causes changes in pigmentation but does not affect the bones as the other treponemal illnesses are capable of doing. Thus yaws, endemic nonvenereal syphilis, and syphilis are all possibilities for the American infection in question, as is perhaps some other treponemal infection now extinct. Of these candidates, however, venereal syphilis seems the least promising, because of an apparent absence of congenital syphilis in the skeletal material.

Brenda Baker and George Armelagos (1988), in providing us with the latest extensive review of the literature on the treponematoses, have also provided us with the latest hypothesis as to their origin and antiquity. Given the scarcity of skeletal evidence of treponematosis in the Old World, and its abundance in the Americas, they suggest that treponematosis is a relatively new disease that arose in the Americas as a nonvenereal infection that spread by "casual contact." However, after the men of the Columbian voyages contracted the illness and carried it back to Europe, the circumstances of urban environments transformed the nonvenereal American disease into the venereal syphilis that raged across Europe and much of the globe for the next century or so before subsiding into the considerably more tame disease we know today.

Clearly, then, despite decades of debate about the nature of the treponematoses, there is still no agreement on their place or places of origin, nor on their antiquity. It does seem to be generally accepted that a transition in the method of transmission of the treponemal syndromes can be, and was, rather swiftly brought on by changing environmental and social circumstances, and thus, that syphilis is the youngest of these syndromes. But like so many other surveys of the treponematoses this one, too, must end with the hope that more evidence will be uncovered in the future to shed light on the many continuing paradoxes posed by this fascinating family, which may or may not consist of a single member.

Kenneth F. Kiple

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