A sensitive and reliable quantitative immunohistochemistry technique to evaluate the percentage of Trypanosoma cruzi-infected tissue area.

Quantification of parasites in the context of Chagas disease is required to monitor the treatment with benznidazole, disease-associated cardiomyopathies and graft rejection after heart transplantation. As parasitological exams lack sensitivity, Real Time Polymerase Chain Reaction (rt-PCR) has emerged to evaluate the parasite load in blood samples and cardiac biopsies. However, despite its higher sensitivity, rt-PCR does not provide information on the location and distribution of amastigote nests within infected tissues, the characterization of inflammatory infiltrates or changes to tissue architecture. On the contrary, a sensitive immunohistochemistry technique (IHC) could fill these gaps. In the present study, a quantitative IHC exam was standardized and validated by testing adipose and cardiac tissues of experimentally infected mice containing variable parasite load levels of T. cruzi assessed by a sensitive Sybr Green rt-PCR with kDNA primers. Tissues were divided into four groups according to the parasite load: group A- 100 parasites/50 ng of DNA; group B -10 parasites; group C - around 1 parasite and group D - less than 1 parasite/50 ng/DNA. IHC was able to detect T. cruzi in the four groups, even in group D tissues containing fractions of a single parasite/50 ng of DNA sample according to rt-PCR. In conclusion, a highly sensitivity and reliable quantitative immunohistochemistry technique was developed and is proposed to estimate the percentage of T. cruzi-infected tissue area in chagasic patients presenting with cardiomyopathies, as a complementary test to rt-PCR.

Mitochondrial and satellite real time-PCR for detecting T. cruzi DTU II strain in blood and organs of experimentally infected mice presenting different levels of parasite load.

The choice of cost-effective molecular methods for diagnosing and monitoring of Chagas disease before and after treatment is crucial in endemic countries with high patients' demand and limited financial resources. To this end, a kDNA was compared to a satellite real-time quantitative PCR (sat-qPCR), both amplifications using Sybr Green instead of Taqman hydrolysis probes. Non-isogenic Swiss albino mice were infected with a small inoculum of the highly virulent and partially resistant to benznidazole Y strain, belonging to T. cruzi discrete typing unit II (DTU-II) that predominates in Atlantic and Central Brazil. DNA from EDTA-blood samples and 10 organs of mice containing high, moderate and low parasite load levels were extracted by a highly used commercial kit and tested in triplicate, showing no disagreements between the two qPCRs. The melting temperature of positive samples was 79.8 °C ±â€¯1 °C for satellite-DNA and 78.1 °C ±â€¯1 °C for kDNA. DNA from genetically-related parasites such as Leishmania sp. showed no cross-reactions, but the sympatric T. rangeli was detected by both qPCRs, more effectively by kDNA than the satellite system, which required the equivalent of 50 parasites to give a positive result. Samples from infected mice, regardless of the type of biological matrix (blood or organ samples) or the parasite load gave positive results by both qPCRs. The sensitivity of sat-qPCR was 2 × 10-3 parasite or 240 target copies, and for kDNA, 2 × 10-4 parasite or 24 target copies. Regarding repeatability and reproducibility, the coefficient of variation (CV) was always < 25% in both assays; linearity of sat-qPCR was 0.991 (±0.002) and 0.991 (±0.008) for kDNA qPCR. In most collection times, the median Ct values found in blood and organs provided by sat-DNA and kDNA qPCRs were similar. In conclusion, although kDNA qPCR achieved a better analytical sensitivity, sat-qPCR gave better specificity results. Nevertheless, further research is intended to test other T. cruzi DTUs and chagasic patients' samples before these cost-effective techniques are incorporated into diagnostic routines.

[Seropositivity for Chagas disease among blood donors in Araraquara, State of São Paulo, between 2004 and 2008]. / Soropositividade para doença de Chagas entre doadores de sangue em Araraquara, Estado de São Paulo, no período de 2004 a 2008.

INTRODUCTION: Blood transfusion is an important potential source of Chagas disease transmission. METHODS: Files from the Araraquara Regional Blood Center were checked regarding the tests results for Chagas' disease between January 2004 and December 2008. RESULTS: Positive serology was diagnosed in 0.04% of 49,541 blood donations that were performed. Seropositive individuals were aged between 51 and 60 years-old. CONCLUSIONS: The low rate of seropositive donors may reduce the risk of transfusion transmission of Chagas disease. The high occurrence of inconclusive results indicates that the diagnostic methods must be improved.

Soropositividade para doença de Chagas entre doadores de sangue em Araraquara, Estado de São Paulo, no período de 2004 a 2008 / Seropositivity for Chagas disease among blood donors in Araraquara, State of São Paulo, between 2004 and 2008

INTRODUÇÃO: A transfusão sanguínea é uma fonte potencial importante para transmissão da doença de Chagas. MÉTODOS: Foi verificado, nos arquivos do Hemonúcleo Regional de Araraquara, o resultado dos exames para doença de Chagas entre janeiro de 2004 e dezembro de 2008. RESULTADOS: Foram diagnosticadas com sorologia positiva 0,04 por cento das 49541 doações de sangue realizadas. A idade dos soropositivos situou-se entre 51 e 60 anos. CONCLUSÕES: O baixo índice de doadores soropositivos pode reduzir o risco de transmissão via transfusional da doença de Chagas. A alta ocorrência de resultados inconclusivos indicam que os métodos diagnósticos devem ser melhorados.

INTRODUCTION: Blood transfusion is an important potential source of Chagas disease transmission. METHODS: Files from the Araraquara Regional Blood Center were checked regarding the tests results for Chagas' disease between January 2004 and December 2008. RESULTS: Positive serology was diagnosed in 0.04 percent of 49,541 blood donations that were performed. Seropositive individuals were aged between 51 and 60 years-old. CONCLUSIONS: The low rate of seropositive donors may reduce the risk of transfusion transmission of Chagas disease. The high occurrence of inconclusive results indicates that the diagnostic methods must be improved.