Chagas disease: Performance analysis of immunodiagnostic tests anti-Trypanosoma cruzi in blood donors with inconclusive screening results

ABSTRACT Background: The screening of Trypanosoma cruzi-infected blood donors using two serological techniques frequently leads to conflicting results. This fact prompted us to evaluate the diagnostic performance of four "in-house" immunodiagnostic tests and two commercially available enzyme-linked immunosorbent assays (ELISAs). Material and Methods: One hundred and seventy-nine blood donors, whose screening for Chagas disease was doubtful, underwent three in-house ELISAs, one in-house immunoblotting test (TESA-blot), and two commercial ELISAs (bioMérieux and Wiener) in an attempt to define the presence or absence of infection. Simultaneously, 29 donors with previous positive results from three conventional serological tests and 30 donors with constant negative results were evaluated. Results: The ELISA-Wiener showed the highest rate in sensitivity (98.92%) and the ELISA-bioMérieux, the highest specificity (99.45%), followed by the TESA-blot, which showed superior performance, with lower false-negative (2.18%) and false-positive (1.12%) rates. In series, the combination composed of the TESA-blot and ELISA-bioMérieux showed slightly superior performance, with trifunctional protein deficiency (TFP) = 0.01%. Conclusion: Our study confirms the high sensitivity and specificity of commercial kits. To confirm the presence or absence of T. cruzi infection, the combination of TESA-blot and ELISA-bioMérieux may be suggested as the best alternative. Individually, the TESA-blot performed the closest to the gold standard; however, it is not commercially available.

Canine visceral leishmaniasis and Chagas disease among dogs in Araguaina, Tocantins / Leishmaniose visceral canina e doença de Chagas em cães de Araguaina, Tocantins

The present study analyzed serum samples from 111 male and female dogs of various ages from the municipality of Araguaína in the State of Tocantins, Brazil. Serological diagnosis of canine visceral leishmaniasis (CVL) was initially performed at the Central Laboratory (Laboratório Central ­ LACEN) of Araguaína, resulting in 61 positive samples by an indirect immunofluorescence assay (IIFA) (≥1:40) and 50 non-reactive samples. The same samples were analyzed at the São Paulo Institute of Tropical Medicine (Instituto de Medicina Tropical de São Paulo ­ IMTSP) by an enzyme-linked-immunosorbent assay (ELISA), resulting in 57 positive samples (51.35%) and 54 negative samples (48.64%). The Kappa coefficient of agreement between the tests was 0.74. The serum samples were also subjected to a diagnostic assay for Trypanosoma cruzi (Trypomastigote Excreted/Secreted Antigens -TESA-blot) that detected five suspect animals; three of those animals were positive for leishmaniasis by ELISA but negative by IIFA. These findings suggest that the canine population of Araguaína may be simultaneously infected with Leishmania chagasi and T. cruzi. The results obtained demonstrate the difficulty of using serology to detect CVL, thus emphasizing the necessity for a reference test to diagnose CVL, particularly in regions where the infection is endemic.

Neste estudo foram analisadas amostras de soros de 111 cães machos e fêmeas, de idades variadas, provenientes do município de Araguaína, estado do Tocantins, Brasil. O diagnóstico sorológico para leishmaniose visceral canina foi realizado, inicialmente, no Laboratório Central (LACEN) de Araguaína, resultando em 61 amostras positivas na Reação de Imunofluorescência Indireta - RIFI (≥1:40) e 50 amostras não reativas. As mesmas amostras foram analisadas no Instituto de Medicina Tropical de São Paulo (IMTSP) pelo Enzyme-Linked-Immunosorbent Assay (ELISA), sendo 57 amostras positivas (51,35%) e 54 amostras negativas (48,64%), com coeficiente de concordância entre os testes (Kappa = 0,74). Os soros foram submetidos também a um teste de diagnóstico para Trypanosoma cruzi (Trypomastigote Excreted/Secreted Antigens-TESA-blot), o qual detectou cinco animais suspeitos, dos quais três foram positivos para leishmaniose no ELISA, mas negativos na RIFI. Estas observações mostram que a população canina de Araguaína pode também estar infectada simultaneamente com Leishmania chagasi e T. cruzi. Estes resultados mostram a dificuldade da sorologia na detecção da Leishmaniose Visceral Canina (LVC), reforçando a necessidade de um teste de referência para o diagnóstico da leishmaniose visceral canina, principalmente em regiões endêmicas para tais infecções.