Scratching the site of the bite cause the trypomastigotes to enter the host through the wound , or through intact mucous membranes , such as the conjunctiva . Once inside the host , the trypomastigotes invade cells , where they differentiate into intracellular amastigotes . The amastigotes multiply by binary fission and differentiate into trypomastigotes , which are then released into the bloodstream . This cycle is repeated in each newly infected cell . Replication resume only when the parasites enter another cell or are ingested by another vector . ( See also : Life cycle and transmission of T. cruzi )