Chagas' disease diagnosis: Comparative analysis of parasitologic, molecular, and serologic methods

During the course of chronic chagasic infection, low parasitemia levels pre vent parasite detection by current techniques such as hemoculture and xenod iagnosis. Since serologic tests have sensitivity but lack specificity, mole cular assays based on the polymerase chain reaction (PCR) have been propose d as alternative tools for parasite detection in individuals with chronic C hagas' disease. A variable degree of PCR efficiency has been reported in th e literature and illustrates the need for further evaluation of large numbe rs of chagasic patients. In this study, we compared an optimized PCR techni que with hemoculture and complement-mediated lysis (CoML) in 113 individual s from or living in endemic areas of Brazil who had conventional serologic results that were either positive, negative, or inconclusive. The PCR ampli fication yielded positive results in 83.5% (66 of 79) of individuals with p ositive serology, 47.6% (10 of 21) with negative, serology, and 46.2% (6 of 13) with inconclusive serology. Of 10 patients with negative serology and positive PCR result, eight (80%) had positive CoML, indicating that they co uld have been chagasic but were not mounting immune responses. The PCR resu lts ware also positive for all individuals who had positive hemoculture, fo r 37 individuals with negative hemoculture and positive serology, and for t wo of six individuals with inconclusive serology and negative hemoculture. Thirteen individuals living in nonendemic areas who had negative serology w ere used as a negative control group: 100% had negative PCR results. Our re sults show that the optimized PCR protocol used here was very sensitive in detecting the presence of Trypanosoma cruzi in chronic chagasic patients. T he PCR and CoML results were well correlated in all of the groups studied, which suggests that our PCR protocol may be effective in the evaluation of cure in patients who receive anti-parasite treatment.