PUBLIC-HEALTH ASPECTS OF YAWS 



By Andrew Watson Sellards 



Of the Bureau of Science, Manila 



DISTRIBUTION 



Yaws is one of the comparatively few diseases that are 

 limited rather sharply to the Tropics. It encircles the globe 

 in the Torrid Zone, but curiously enough it does not spread 

 when introduced into temperate climates. There are a few 

 records of an occasional isolated case contracted outside 

 of the Tropics, but the disease does not gain a foothold there. 

 Maxwell (8) states that yaws is imported into China from the 

 Straits Settlements from time to time, but soon dies out. These 

 statements apply to the distribution of yaws as it occurs to- 

 day ; it is believed by some authors that certain of the diseases 

 formerly endemic in Ireland may have been yaws. 



In several instances the geographical restriction of infectious 

 diseases is readily explained by the corresponding limitation 

 of an essential insect vector. The interest which such sharp 

 limitation arouses is well illustrated by the striking though 

 incompletely studied example of verruga peruviana and oroya 

 fever. These diseases occur in the Andes Mountains and are 

 endemic at altitudes of approximately 1,500 to 7,000 feet (500 

 to 2,300 meters). Patients when removed to higher or lower 

 altitudes do not serve as foci of infection. Moreover, suscepti- 

 ble individuals may remain in the infected zones during the 

 daytime with impunity, but before nightfall they must pro- 

 ceed to a higher or lower altitude. Hence the inference is 

 drawn that these diseases are transmitted by a night-flying 

 insect limited to this region. 



Even within the Tropics it is commonly stated that yaws 

 is restricted to the lower altitudes. Bahr(2) noted in Ceylon 

 that people living at altitudes higher than 800 feet (260 

 meters) rarely contract the disease, even though the surround- 

 ing lowlands are thoroughly infected. A striking exception 

 has been reported by Ricono(lO) who describes eight cases in 



