You would need to do a controlled study just like we due with pharmaceuticals, and test the new treatment against the current treatment to see its efficacy. It would take several years and would have to go through several stages and trials before you could confidently prescribe it as a treatment for Chagas disease. Just because it has been used for several years, I wouldn't cut any corners because for all we know, the therapeutic effects that the indigenous people were feeling could simply be a placebo effect.
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