Strategies for prevention of transfusion-associated Chagas' disease.

Available epidemiological data indicate that Chagas' disease, a zoonosis caused by the flagellate protozoan parasite T cruzi, is a very important medical and social problem in Latin America. More than 60% of T cruzi-infected individuals have migrated to urban areas, in both endemic and nonendemic countries. Thus, with the implementation and maintenance of regular vector control programs in some countries, allogeneic blood transfusions have been the main mechanism for the continuation of this endemy. The risk of infection after transfusion of a unit of T cruzi-infected blood product depends mainly on the amount of blood transfused, parasite concentration in the infected transfused blood unit, and the recipient's immunological status. Current strategies to prevent transfusion-associated Chagas' disease include the identification of T cruzi-infected blood donors by predonation questionnaire, serological tests for T cruzi antibodies, and the treatment of the blood collected with gentian violet. Because T cruzi infection is lifelong, and most infected persons are asymptomatic, the identification of high-risk blood donors by a predonation questionnaire is relevant in nonendemic countries but this strategy seems to be of limited usefulness for donor deferral in endemic areas. Because T cruzi antigens are shared by other parasites, the serological diagnosis of T cruzi infection is complex yielding both false-positive and false-negative results. Although sensitive, the tests currently available for the serodiagnosis of T cruzi infection lack specificity and a more specific, confirmatory test is still needed for the routine confirmation of T cruzi chronic infection. In areas of high endemicity or where serological screening is not available, the risk of T cruzi transmission by blood transfusion may be reduced by the addition of gentian violet to the collected blood. The use of gentian violet, alone or combined with ascorbic acid and light, effectively inactivate T cruzi present in donor blood; however, the long-term toxicity of this agent for blood recipients is still an open issue. In conclusion, the prevention of TA-CD is based on various strategies that are not mutually exclusive. Blood donor education, identification of putatively infectious blood donors by questionnaire or serological screening tests, and methods of parasite inactivation may significantly reduce the transmission of T cruzi by allogeneic blood transfusions.