Both trypomastigotes and intracellular amastigotes develop in infected mammals, the former in the bloodstream and the latter mainly in macrophages and muscle cells. The trypomastigotes do not multiply but disseminate the infection around the body of the mammalian host and also serve to infect the vectors (large blood-sucking bugs of the subfamily Triatominae, family Reduviidae (Hemiptera); both sexes feed exclusively on blood). Trypomastigotes ingested by a feeding bug change into epimastigotes in the midgut, undergo division, and are moved back along the bug's gut as the blood meal is digested. In the hindgut they transform into small metacyclic trypomastigotes (which do not divide); these forms are expelled when the bug defecates while, or just after, feeding, and enter through the wound made by the bug's proboscis. The insects often feed on sleeping persons, and faecal matter may be transferred by the scratching or rubbing fingers of a …