Chagas' disease: evaluation of a rapid immunochromatographic assay for the detection of anti-Trypanosoma cruzi antibodies
Abstract number: P970
Gabrielli S., Faraone A., Bonelli S., Mantella A., Strohmeyer M., Filardo S., Bartalesi F., Bejarano V., Cancrini G., Bartoloni A.
Objectives: Chagas disease, caused by Trypanosoma cruzi, affects 7.6 million of people in Latin America. A survey was carried out to assess its prevalence in two rural Bolivian communities (Bartolo, Chuquisaca Dep., and Casas Viejas, Santa Cruz Dep., Bolivia), and to evaluate the performance of Chagas Quick Test, a new immunochromatographic assay (ICT) to detect anti-T. cruzi antibodies.
Methods: 226 subjects were enrolled (121 males, 105 females); the infection was evaluated using a conventional T. cruzi IgG ELISA test, the above mentioned ICT, and the microscopic analysis of Giemsa stained thick smears. Individuals showing discordant ICT-ELISA results underwent molecular analyses. DNA was extracted from blood dried on filter paper using Chelex-100® method. T. cruzi nuclear DNA was amplified using primers TCZ1 and TCZ2 for the first reaction and TCZ3 and TCZ4 for the nested amplification. Amplicons were sequenced and subjected to GenBank to give the most likely identification.
Results: ELISA was positive in 142 people (62.8%); infection rate increased according to age from 15.3% in 19 years old individuals, to 100% in over sixties, independently by sex. No parasitemic individuals were found by hemoscopic analysis. A total of 159 subjects (70.3%) proved positive to ICT; all subjects positive to ELISA had a positive result (relative sensitivity 100%), with an intensely coloured test line. Moreover, 17 individuals negative to ELISA proved positive to ICT, with a very faint test line. The agreement between ELISA and ICT was 92.4% (209/226) (kappa 0.83). Molecular assays confirmed the infection in 4 serologically discordant subjects.
Conclusions: seroprevalence of T. cruzi infection in the study population is very high, and increases rapidly with the age, showing that parasite active transmission occurs universally. Negative results obtained by microscopy fit in with the low sensitivity of this diagnostic tool conditioned by the low parasitaemia in chronic infected people. Chagas Quick Test showed an almost perfect accordance with the conventional ELISA. PCR confirmed to be an useful complement to serological methods; it contributed to increase ELISA sensitivity and partially corroborated ICT results, supporting the advice that very faint test lines have to be considered as likely positive. Further investigations are needed to define the infectious status of subjects with discordant serology and negative PCR assay.
|Session name:||18th European Congress of Clinical Microbiology and Infectious Diseases|
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