Acute fear of the disease may have even driven human settlement patterns in South America. The archaeologist James Kus, a retired professor at California State University, Fresno, believes that the Inca site of Machu Picchu may have been chosen, in part, because of the prevalence of mucosal leish. “The Incas were paranoid about leishmaniasis,” he told me. The sand fly that transmits leish can’t live at higher altitudes, but it is widespread in the lowland areas where the Inca grew coca, a sacred crop. Machu Picchu lies at just the right altitude: too high for leish, but not too high for coca;
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