Medical understanding of the relationship between the different syndromes of treponematosis—bejel, yaws, and syphilis—was aided greatly by the work of a brilliant clinician working in the mid-twentieth century, Ellis Herndon Hudson (1890–1992). Among other investigations that have not been given their due by historians, he published an innovative study of endemic treponematosis titled Non-Venereal Syphilis: A Sociological and Medical Study of Bejel (1958). Hudson used the term “non-venereal” rather than “endemic” quite deliberately in his title, to impress upon readers his finding that bejel was devoid of the immoral connotations long associated with syphilis. He wanted them to understand that bejel, a disease of dry climates that thrived in the Middle East, was a childhood disease among the Bedouin, while syphilis was a disease of adults who lived in towns and cities. On the appearance of syphilis in urban areas, Hudson wrote, for example: “Venereal syphilis has no predilection for a particular climate, but it is found more in cities, where money is in freer circulation and amusements more organised; it is a companion of prostitution and other social behaviour problems.” He also cited a study of treponematosis in Bos nia, concluding that “the prevalence of endemic syphilis was inversely proportional to the population.”

Hudson's seminal studies based on research in Syria and Iraq noted that habits of cleanliness, including keeping children fully clothed and indoors much of the time, were more common among urban dwellers, and he hypothesized that these conditions had led to the evolution of the venereal form of treponematosis in ancient cities. To this crucial observation we should probably add a consideration of status, for elites led a very different lifestyle from the peasantry in stratified societies. Few elite children would be found scantily clad playing in the dirt of the stable yard or street, and generally not in the company of their social inferiors who might pass on a painful and unsightly disease through skin-to-skin contact or shared drinking vessels. The very fact that some people—whether urban dwellers, elites, or perhaps even Jews who observed strict rules on hygiene, clothing, and food consumption—did not become infected with endemic treponematosis in childhood made them susceptible to the venereal form of the disease as adults.