The aromatic amino acid tryptophan plays a critical role in the pathogenesis of infection caused by trypanosomatid parasites, including Trypanosoma cruzi (Chagas disease), T. brucei rhodensiense and T. brucei gambiense (African sleeping sickness), and the various Leishmania species. During the parasite life cycle, tryptophan influences metabolism, changes in morphology, and movement between the invertebrate vector and the vertebrate host. In the vertebrate host, tryptophan and its metabolites influence the host inflammatory response and the transition to chronic infection. In this chapter, we review current knowledge regarding the tryptophan and kynurenine pathways in trypanosomatid parasitosis, present genomic evidence supporting their importance in trypanosomatid infections, and discuss applicability in development and assessment of new treatment modalities.
