Inca and colonial settlement,coca cultivation and endemic disease in the tropical forest

A configuration unfolds from early colonial chronicles, the archaeological record and epidemiological evidence that infectious disease was a critical factor in constraining durable pre-Hispanic settlement in the Amazon forest. The Incas' main interest in the wet tropical valleys beyond the mountain front, particularly those northeast of Cuzco the capital, was to grow coca. Quest for the sacred leaf justified intrusions into a hyperendemic zone of mucocutaneous leishmaniasis, a complex protoxoal disease carried by sand flies that results in dermal lesions and grotesque necrosis of the face. In an effort to avoid this disfiguring disease, the Incas carried on trade relations with forest tribes, subjugated some of these tribes to clear the forest for them, and shifted people from analogous climates elsewhere. The most important mechanism was to control the length of the work period of coca labourers from the highlands. Traditional vertical migration of Andean natives and siting of pre-Conquest dwelling sites largely above the zone of leishmaniasis contraction suggest an ancient geographical pattern of disease avoidance. After the Conquest, disease mortality was very high, as Spaniards expanded coca cultivation but disregarded many of the indigenous safeguards. Adjustments to an insalubrious yet compelling environment are more persuasive than agricultural limitations in understanding the deep-seated past aversion of highland Indians to sustained occupance of the selva.