Eighty percent of T. cruzi transmission occurs between mammals by way of blood-sucking triatomine bugs (multiple species are capable of transmission – see “Vector” section for more information.) Triatomine bugs first acquire the parasite by biting an infected individual and ingesting trypomastigotes. The trypomastigotes mature into epimastigotes, then metacyclic trypomastigotes, in the digestive system of the insect. When the insect takes a blood meal from a second individual, it also commonly passes feces onto the skin near where it bit, which may contain metacyclic trypomastigotes. Those trypomastigotes can infect the bitten individual by entering the bite wound or penetrating mucosal membranes. Often times, the individual will aid the parasite in entering by scratching the site of the bite and spreading the feces with their hand, often to their eye.
Transmission can also occur through blood transfusion. A study of twelve countries in South and Central America in 1993 and 1994 showed that the risk of acquiring T. cruzi infection when receiving a blood transfusion was higher than the risk of acquiring HIV, hepatitis B virus, hepatitis C virus, and Syphilis through a similar procedure. However, The rate of T. cruzi transmission in blood transfusions has been decreasing since 1990, which is thought to be primarily due to improved vector control programs. Additionally, there have been efforts to increase blood screening for T. cruzi and require a questionnaire from blood donors regarding their exposure to T. cruzi and associated endemic areas.
Child receives a blood transfusion
Congenital transmission of T. cruzi is also possible and was shown, by one study conducted in Santa Cruz, Bolivia, to occur in 5% of infected mothers. Congenital transmission is more likely to occur if the mother is in the acute phase of infection. Certain strains of T. cruzi are more efficient at crossing the placenta and therefore congenital transmission is often found in pockets of higher incidence, surrounded by regions of lower incidence.
Finally, food and water that is contaminated with the feces of triatomine bugs can transmit T. cruzi, as the parasites are present in the feces and can survive for periods outside a host.