Distribution and Incidence

As a result of the intensive campaign against yaws that was carried out in the 1950s by the World Health Organization, the disease is no longer present in many populations where previously it was a serious health threat. Nevertheless, some comment on its previous geography and ecology is worthwhile, particularly as this may tell us something about its adaptive evolution. Indeed, it would seem true to say that of the treponematoses, yaws is the one that appears to be adapted to infecting human populations in tropical or subtropical climates (so there are the combined factors of heat, humidity, poor living conditions and hygiene, and limited clothing worn). Thus although it has been estimated that 80 percent of the yaws-afflicted populations lived within the mean annual isotherm of 80°F, it has to be recognized that various environmental and social factors must be taken into account in order to understand the variable incidences of this disease.

Exceptions to the geographic rules that might be seen to govern this condition are not difficult to find. For instance, in the case of mean annual rainfall, yaws was usually found in areas where there is 50 to 75 inches of rain a year, but it has occurred in drier climates as represented by parts of Madagascar, India, and Bolivia. In all, there were probably some 50 million yaws cases in the world half a century ago.

In the 1940s and early 1950s, estimates of yaws prevalence were made in various areas of the world, partly in relation to yaws eradication programs. Although regional figures have now dropped radically, it is pertinent to the history of the subject to note the extent of the previous evidence, and the variation found. In the case of most of the New World, although yaws was probably introduced by slaves centuries ago, no significant incidence has remained into this century. However, in the Caribbean area, which had been varyingly affected by the slave trade, yaws displayed some contrasts. Thus, Cuba was reported as having a low frequency of yaws, whereas in Haiti 60 to 80 percent of the rural popula tion were estimated to have had yaws. Similarly, Jamaica registered 70 to 80 percent frequency figures in some districts. In South America, Brazil was known to have many cases, especially in the northern regions where 350,000 cases were at one time noted. In Colombia, there was also regional variation, with the Pacific coast regions reporting 80,000 cases (with a general rate of 43.5 per 100,000). In contrast to these two countries, yaws appears to have been only a very modest health problem in Peru and Venezuela.

In the Old World, the disease was endemic in parts of Africa, Asia, and the Pacific. In Africa, quite high frequencies were found in some areas, although possibly the highest incidences occurred in Asia and the Pacific. In 1945, in the area then designated the Belgian Congo, there were 325,994 cases; and, in the same year, Tanganyika recorded 69,000 cases. Also about this time, frequencies in French West Africa varied from 0.02 percent (Niger) to 6.3 percent (Ivory Coast). French Equatorial Africa similarly had frequencies ranging from 0.1 percent (Chad) to 4.3 percent (Gabon), and the regional incidences in Uganda varied from 2 percent to 17.5 percent.

Yaws was also an important disease in the more tropical areas of Asia. In the Indian territory of Madhya Pradesh, 5.6 percent of the population was recorded as having yaws. Indonesia may have had as many as 10 million yaws cases before its anti-yaws campaign had any effect, and in some areas possibly 60 percent of the population had some experience of the disease. Thailand may also have had some 1.4 million cases prior to its current reduction, and in Laos, too, 1 to 15 percent of the population was thought to be affected.

Territories of the Pacific area showed some surprising frequencies, and clearly the relatively small populations of most of the islands did not prevent the spread of this disease. It was frequent on Guam, and, in 1953, on Simbo Island 20 percent of the general population had experienced yaws (and 78 percent of the children had been affected at some time). Also in the early 1950s, it was recorded that 17 percent of the population of Wallis Island and 18 percent of 80,000 Western Samoans had yaws.

This evidence of yaws in various parts of the world just prior to the antibiotic campaigns for its eradication helps to emphasize points of historical interest. One is that yaws probably had a relatively limited distribution in the New World. In some areas where notable frequencies have been attained, the phenomenon was probably linked to the history of the arrival of yaws-affected African slaves on the one hand, and environmental and social variable conducive to the survival and expansion of yaws on the other. A second point of historical interest is that in the Old World it is clear that yaws affects widely divergent ethnic groups distributed from Africa to the Pacific and that the history of the disease in these areas is likely to be hundreds if not thousands of years old.

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