Abstract
BackgroundTrypanosoma cruzi multiplies and differentiates in the digestive tract of triatomine insects. Xenodiagnosis (XD) is a parasitological tool in which the insect vectors acts as a biological culture medium to amplify and detect T. cruzi infection in mammals. The sensitivity of XD has been overcome by the application of PCR in fecal samples (FS) of XD (PCR-XD). In this study, T. cruzi amplified in Triatoma infestans fed by XD on individuals with chronic Chagas disease (CChD) is quantified by real-time PCR (qPCR-XD).FindingsUnder informed consent, 100 individuals were evaluated. In 21 of them XD, PCR-XD and qPCR-XD were positive. For the contrary, 79 were negative XD. In 58 (73.4 %) and 66 cases (83.5 %) of them, PCR-XD (Fisher’s exact test P = 0.005) and qPCR-XD (Fisher’s exact test: P = 0.037) respectively, were positive. In cases with positive XD, qPCR-XD allowed to establish that in 9/21 cases (42.9 %) the parasite burden fluctuated between 100 and 1,000 par. eq./ml. Otherwise, in 32/79 (40.5 %) cases with negative XD, a parasite burden between 1 and 10 par. eq./ml was determined. All samples showed amplification of exogenous internal control (X12, Ct average: 31.8), so problems in the DNA extraction (excess or loss of genetic material), unspecific amplification and/or inhibition in qPCR-XD reactions were ruled out. Additionally, in all the patients qPCR in blood (qPCR-B) was performed. In the cases with positive XD, the concordance between the positivity of qPCR-XD and qPCR-B was 100 %, nevertheless, the parasite burden in blood was lower and different than XD (Chi-square test: χ2 = 91.82, df = 5, P = 0.0001). In the cases with negative XD the ranges of qPCR-XD and qPCR-B were similar (Chi-square test: χ2 = 6.71, df = 5, P = 0.1520).ConclusionsThis study allowed the detection and quantification of T. cruzi by qPCR-XD in FS of Tr. infestans fed on patients with CChD. The highest parasite burden was observed in positive XD cases. qPCR-XD could be used in different studies related with the complex T. cruzi-vector-host interactions.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1664-5) contains supplementary material, which is available to authorized users.
Highlights
Trypanosoma cruzi multiplies and differentiates in the digestive tract of triatomine insects
The highest parasite burden was observed in positive XD cases. real time PCR or quantitative PCR (qPCR)-XD could be used in different studies related with the complex T. cruzi-vector-host interactions
In 1999, Chile was declared free of transmission of T. cruzi by Triatoma infestans; it is estimated that 140,000 people are infected with T. cruzi in the country, mostly without tripanocidal treatment [36, 37, 50]
Summary
Trypanosoma cruzi multiplies and differentiates in the digestive tract of triatomine insects. The classical xenodiagnosis (XD) [8, 32] has been used as a tool of selection for specific treatment and its posterior evaluation [2, 7, 16], searching for the most effective triatomine species [9], isolation and characterization of T. cruzi DTUs [13, 26, 33, 34, 47], comparison of its sensitivity with other procedures for the detection of T. cruzi in bloodstream [6, 51] and relation parasite cycle-vector [18, 41] In most of these studies, the result of XD has been expressed in qualitative terms, i.e. fundamentally based on the microscopic observation of mobile tripomastigote forms of T. cruzi [11, 23, 39]. The objective of this study is to detect and quantify T. cruzi in Tr. infestans fed by XD on individuals with CChD by real-time PCR (qPCR-XD)
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