Fig. 1

Schematic of the three major Leishmania stages in sand flies. Shortly after ingestion (1, red arrow) of the blood meal, promastigotes are localized in the midgut lumen, in the blood-meal bolus surrounded by peritrophic matrix (2; 1 day post blood meal [PBM]). Leishmania wait until the peritrophic matrix is broken down, and then at the end of the digestive process they enter the endoperitrophic space and attach to the epithelial wall (3; > 4 days PBM). Finally, where parasites have migrated anteriorly to the thoracic midgut, the stomodeal valve of the fly and the human-infective metacyclic forms differentiate from the earlier stages (4, 5; > 9 days PBM).