Chagas disease: a threat to safe blood transfusion

Abstract

Chagas disease affects approximately 8 million infected people in Mexico and Central and South America and causes 12 500 deaths annually; 41 200 new cases are reported annually (2006). Coordinated multicenter programmes have decreased about 70% of new infections in South America due to the interruption of vectorial and decreased blood transfusion transmissions. Migration of the infected population from rural areas to urban centres in endemic and non‐endemic countries led to the urbanization and globalization of Chagas disease. Chagas disease is now an emerging disease in non‐endemic areas, where congenital, blood and organ transplant transmissions are associated with reactivation of chronic Chagas disease in patients under immunosuppression or HIV infection. Recent initiatives in non‐endemic countries have been implemented to control its transmission by blood transfusion and transplants of organs. Most of the infected people were asymptomatic individuals in the chronic phase of the disease, characterized by and low and intermittent parasitemia and diagnosed by serological tests. In endemic countries, universal mandatory screening tests for detection of Trypanosoma cruzi antibodies dramatically reduced blood transfusion transmission. In non‐endemic countries, where transfusion represents the most important way of transmission, different strategies have been registered: (1) blood donor selection and deferral; (2) blood donation testing; (3) blood donation testing in people who lived in endemic areas. Questionnaires containing well‐defined questions help to identify patients from endemic areas and their epidemiological data but are of limited value since they depend on donor information. High‐performance serologic tests were reported for the detection of anti‐T. cruzi antibodies like ELISA with epimastigotes or trypomastigotes or recombinant antigens, chemiluminescent, immunoblot and radioimmunoprecipitation assays. Almost 100% of sensitivity and specificity were registered when tested in samples of well‐defined chronic chagasic patients but gold standards are not validated in circumstances of low prevalence of the disease. Additionally, their value in cases of inconclusive results (one positive test and other negative or doubtful results) was not known. Unfortunately, molecular methods are less sensitive than serology for the chronic phase of the disease (45–100% sensitivity) and were not reliable for screening tests in blood banks. Perspectives of the reduction of parasites by photochemical treatment and ultraviolet (crystal violet, methylene blue, amotosalen, riboflavin, thiopirilium) were reported sometimes with slight changes in the blood products. However, the main challenge is to demonstrate their value for prevention of a broad spectrum of agents transmitted by blood transfusion (including príon disease) and inactivation of low parasite load. In summary, questionnaires including specific questions about donor epidemiology and high‐performance serologic tests have been useful for blood bank screening. The cost–benefit–effectiveness analyses of universal serologic screening vs. serologic screening of selected donors depend on the prevalence of positive donors and should be evaluated in different regions. Finally, as pathogen inactivation methods may represent remarkable improvement in blood bank transfusion, efforts from the academia are necessary to prove their safety and effectiveness, and from blood banking–transfusion medicine community and public regulators to their implementation aiming to increase the safety of blood transfusion for patients around the world.