Blood transfusions are the second most common mechanism of transmission of Chagas' disease to people in Latin America, Europe,and the United States. Blood transfusions enable T. cruzi to travel beyond its native tropical and semitropical zones. Latin American countries are major exporters of blood and organs; this makes the spread of chagas a worldwide problem. In Brasil, 10,000 to 20,000 cases of chagas occur every year through blood transfusions, and Bolivia suffers from a high rate of infected blood. High percentages of infected blood are found in rural migrants and low-income donors who live in infested areas and need money.

The transmission of the parasite is dependent upon the screening of donors. Measures are being adopted by some Latin American countries to help curb the infection of the blood supply, but many countries have not implemented sufficient screening measures. Medical policies in some countries have caused patients to seek organs from other sources. Organs being sold on the black market bring the parasite to unsuspecting people. Additionally, recipients of donated organs are usually under immunosuppressive treatment after surgery, thereby putting them at even more risk of T. cruzi infection.