The Trypanosoma cruzi is a protozoan which causes the Chagas disease. It is transmitted to man through the intervention of a blood-sucking insect which acts as a vector (kissing bug). The Trypanosoma cruzi is found in the flowing blood of infected persons and animals during the acute period of the disease. In this circulating phase of the parasite, the T cruzi is called trypomastigote, which is elongated, measuring approximately 20 microns, and has a thin undulating membrane that runs the full length of its body.
However, when the kissing bug insect sucks blood out of an infected person, the T cruzi goes into the epimastigote phase or stage, where it reproduces through binary fission as it becomes infectious, ending up in the insect's digestive system as metacyclic trypomastigote. When the kissing bug sucks the blood out of another person, it usually defecates on the person's skin. Since the insect bite itches, the person scratches the tiny lesion, inadvertently rubbing in the parasite-containing insect feces into the mucous membrane underneath the skin, ending up in the circulating blood.