COMMENTARY – Gift From Caribbean That Keeps on Giving

By STANLEY M. ARONSON

A 16TH CENTURY Spanish archivist named Oviedo described a contagious disease, largely confined to the skin, afflicting many Caribbean children. His brief description provides an unmistakable profile of a tropical contagion now known as yaws. Because some of its skin lesions resembled raspberries, it was also called framboesia, from the French frambois (raspberry).

The affected child develops multiple painful, raised lesions of the skin, sometimes ulcerating and sometimes accompanied by nocturnal headaches, joint pains and minimal fever. The disease is highly communicable, passing from one poorly clothed child to another through skin contact. The germ of yaws was apparently incapable of penetrating intact skin; and therefore to establish itself as an infection, a small laceration or surface scratch was needed to facilitate the invasion of the germs of yaws.

By the 19th Century the majority of West Indian children were afflicted with yaws as well as the children in other tropical sites, such as equatorial Africa, Southeast Asia, and many of the islands of the southwest Pacific. By the 20th Century, the tropical distribution of yaws was global.

Was yaws always widespread? Or, alternatively, was it made global by enhanced movement of peoples during the 16th through 18th centuries (largely through the shipment of slaves from one continent to another)? Some historians point to Leviticus, Chapter 13, as evidence that yaws had existed in the Middle East before the European colonialization of the Western Hemisphere. Clinicians, however, believe that the Biblical text is much too meager in clinical detail to warrant any conclusion; and most now believe that yaws had been localized in the Caribbean islands and northern South America during the pre-Columbian era, and only with the burgeoning transatlantic traffic did it then spread to virtually all tropical regions.

In 1905, Castellani isolated a corkscrew-shaped bacterium from the skin lesions of children with yaws. He called it Treponema pertenue but admitted that its microscopic appearance was indistinguishable from the microscopic organism (Treponema pallidum) that causes syphilis. Both of the Treponema spirochetes could transmit infection to experimental animals such as rabbits, but the yaws spirochetes tended to form milder experimental lesions.

What then is the relationship, both biologically and historically, between yaws and syphilis? Consider this plausible scenario: Over pre-Columbian centuries yaws prevailed as a near- universal skin affliction of the naked children living in the West Indies and neighboring American mainland. It may have been a more virulent bacterial infection in the very distant past but by the 15th Century the aboriginal Caribbean population had developed a partial immunity to its organisms. In 1492, three ships flying the Spanish flag and captained by Christopher Columbus landed in the West Indies and established intimate contact with the native population. Columbus and much of his crew then returned to Spain, bringing tangible evidence of their discoveries, fragments of gold – and the infection now called yaws.

The European population confronted, for the first time, the spiral-shaped bacterium of yaws now being widely transmitted venereally. And a devastating, horrible disease ensued. The first known epidemic shattered the French armies of King Charles VIII besieging Naples, the troops retreating in disorder and spreading the germs of syphilis, nation by nation, throughout Europe. It was, then, a major morbidity causing severe disability and often death.

The ships of Portuguese Vasco Da Gama rounded the Cape of Good Hope and in 1494 brought syphilis to western India; and by 1505, syphilis had reached China and Japan. The “Caribbean gift” had now become a global burden and a public health hazard of major proportions.

Shortly after World War II, the World Health Organization targeted yaws for possible eradication. Yaws responded promptly to penicillin and a major campaign was then undertaken. Within a decade yaws disappeared from the Western Hemisphere, except for a few isolated pockets in the jungles of Venezuela and Jamaica. Two interventions were deemed responsible for this public-health success: First, an organized public-health campaign identifying and then treating all cases of yaws; and second, an educational program urging parents to clothe their children at an early age, thus interrupting the customary skin-to-skin pattern of yaws transmission. Public-health programs, overcoming the public reticence to talk about sexually transmitted diseases, were similarly directed against syphilis in the 1950 to 1970 interval. Syphilis had also been shown to be curable with penicillin in appropriate dosage and, by 1980, syphilis was reduced to an uncommon affliction.

In 2007, a group of American microbiologists encountered an aboriginal tribe in the interior of Venezuela and noted that many of the children had yaws. The isolated spiral-shaped bacteria were then compared with strains of spirochetes from contemporary cases of syphilis; and by the most sophisticated nucleic-acid analyses, no differences were found between the composition of the two pathogens. They concluded that yaws and syphilis were caused by the same germ but that the differences in clinical profile lay with the genetic backgrounds of two immunologically distinguishable human populations: one, by Darwinian adaptation, somewhat resistant to the germ while the other, exemplified by Europeans, much more vulnerable.

The implications were clear: When humans confront an utterly new infection, it tends to be severe, even devastating (for example, syphilis or AIDS). Then, over the succeeding centuries, humans with more innate resistance tend to survive more readily than those with greater vulnerability, thus producing fewer vulnerable children in the next generation, and gradually then the disease appears to become milder.

Stanley M. Aronson, M.D., a weekly contributor, is dean of medicine emeritus at Brown University ( smamd@cox.net).

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