1. When an infected kissing (Triatominae) bug bites a person, it deposits feces that contain the protozoa. 2. The protozoa enter through the bite wound or through mucosal membranes, such as the clear membrane that covers the eye (conjunctiva). 3. The protozoa then change forms and multiply. 4. They change forms again, enter the bloodstream, and travel to other tissues. There, they change into a form that causes symptoms. 5. When another kissing bug bites an infected person (or animal), it becomes infected. 6–7. Inside the bug, the protozoa change forms and multiply. 8. In the lower part of the bug's gut (hindgut), they change to a form that can move. They are then excreted in the bug's feces.
Image from the Centers for Disease Control and Prevention Image Library.