Chronic Chagas disease: Quantification of Trypanosoma cruzi in peripheral blood and dejections of Triatoma infestans fed by xenodiagnosis in patients with and without cardiopathy

It is not currently known which individuals with chronic Chagas disease (ChD) will develop cardiopathy in a determined period and which will be maintained asymptomatic with normal routine laboratory tests all their lives. The parasite burden is a factor that could explain this different evolution. The objective of this study was to quantify Trypanosoma cruzi burden by real-time PCR in blood (qPCR-B) and dejections of triatomines fed by xenodiagnosis (qPCR-XD) in 90 individuals with chronic ChD untreated, classified according to XD results and the presence or absence of cardiopathy. All individuals came from hyperendemic areas of Chile and participated in the study under Informed Consent. The standard qPCR curves for qPCR-B and qPCR-XD were elaborated with a mixture of known concentrations of T. cruzi strains, performing DNA serial dilutions (1/10) with a dynamic range between 10(5) and 10(-1) parasite equivalents/mL. The TaqMan (R) detection system was applied in a Stratagene Mx3000P thermocycler (Agilent Technologies, USA) with cruzi 1 and cruzi 2 satellite primers. 22.2% and 15.6% of cases with cardiopathy or without cardiopathy were XD positive. There was no significant difference between the groups. The positivity of qPCR-B and qPCR-XD in the positive XD group was 82.35% and 100%, respectively, while in the negative XD group was 55.26% and 42.10%, respectively. A superior qPCR value in chronic ChD patients with and without cardiopathy was determined for qPCR in cases with positive XD and positive qPCR-XD. The receiver operating characteristic (ROC) curve analyses show better accuracy for detecting parasite burden (area under the curve, AUC) for qPCR-XD in comparison to qPCR-B. That is to say, major performance in DNA samples obtained of positive XD (gold standard for viable T. cruzi) detected and quantified by qPCR-XD. A high percentage of cases with XD and qPCR-XD positive (80-100%) have result concordant with qPCR-B. In absence of XD, future challenges are especially related to the low parasitic load of chronic ChD patients treated with trypanocidal drugs and post-therapy parasitological evaluations by qPCR-B. Finally, no statistically significant differences were found between presence or absence of cardiopathy and XD, qPCR-B or qPCR-XD.