The Immunoglobulin M-Shed Acute Phase Antigen (SAPA)-test for the Early Diagnosis of Congenital Chagas Disease in the Time of the Elimination Goal of Mother-to-Child Transmission.

BACKGROUND: Diagnosis of congenital Chagas disease (CChD) in most endemic areas is based on low-sensitive microscopy at birth and 9-month immunoglobulin G (IgG), which has poor adherence. We aim to evaluate the accuracy of the Immunoglobulin M (IgM)-Shed Acute Phase Antigen (SAPA) test in the diagnosis of CChD at birth. METHODS: Two cohort studies (training and validation cohorts) were conducted in 3 hospitals in the department of Santa Cruz, Bolivia. Pregnant women were screened for Chagas disease, and all infants born to seropositive mothers were followed for up to 9 months to diagnose CChD. A composite reference standard was used to determine congenital infection and was based on the parallel use of microscopy, quantitative polymerase chain reaction (qPCR), and IgM-trypomastigote excreted-secreted antigen (TESA) blot at birth and/or 1 month, and/or the detection of anti-Trypanosoma cruzi IgG at 6 or 9 months. The diagnostic accuracy of the IgM-SAPA test was calculated at birth against the composite reference standard. RESULTS: Adherence to the 6- or 9-month follow-up ranged from 25.3% to 59.7%. Most cases of CChD (training and validation cohort: 76.5% and 83.7%, respectively) were detected during the first month of life using the combination of microscopy, qPCR, and/or IgM-TESA blot. Results from the validation cohort showed that when only 1 infant sample obtained at birth was evaluated, the qPCR and the IgM-SAPA test have similar accuracy (sensitivity: range, 79.1%-97.1% and 76.7%-94.3%, respectively, and specificity: 99.5% and 92.6%, respectively). CONCLUSIONS: The IgM-SAPA test has the potential to be implemented as an early diagnostic tool in areas that currently rely only on microscopy.

Trypomastigote Excretory Secretory Antigen Blot Is Associated With Trypanosoma cruzi Load and Detects Congenital T. cruzi Infection in Neonates, Using Anti-Shed Acute Phase Antigen Immunoglobulin M.

Background: Congenital Trypanosoma cruzi infection accounts for an estimated 22% of new cases of Chagas disease in Latin America. However, neonatal diagnosis is challenging, as 9-month follow-up for immunoglobulin G testing is poor, quantitative polymerase chain reaction (qPCR) analysis is not routinely performed, and the micromethod misses ≥40% of congenital infections. Methods: Biorepository samples from new mothers and their infants from Piura, Peru, (an area of nonendemicity), and Santa Cruz, Bolivia (an area of endemicity) were accessed. Infant specimens were assessed using the micromethod, qPCR analysis, and a trypomastigote excretory secretory antigen (TESA) blot for detection of immunoglobulin M (IgM)-specific shed acute phase antigen (SAPA) bands, using qPCR as the gold standard. Results: When compared to qPCR, IgM TESA blot was both sensitive and specific for congenital Chagas disease diagnosis. Cumulative sensitivity (whether only 4 bands or all 6 bands were present) was 80% (95% confidence interval [CI], 59%-92%). Specificity was 94% (95% CI, 92%-96%) in the area of endemicity and 100% in the area of nonendemicity. SAPA bands occurred sequentially and in pairs, and parasite loads correlated highly with the number of SAPA bands present. The micromethod detected infection in fewer than half of infected infants. Conclusions: The IgM TESA blot for detection of SAPA bands is rapid, relatively inexpensive, and more sensitive than the micromethod and may be a useful point-of-care test for detection of congenital T. cruzi infection.

Anti-triatomine saliva immunoassays for the evaluation of impregnated netting trials against Chagas disease transmission.

Insecticide-impregnated nets can kill triatomine bugs, but it remains unclear whether they can protect against Chagas disease transmission. In a field trial in Quequeña, Peru, sentinel guinea pigs placed in intervention enclosures covered by deltamethrin-treated nets showed significantly lower antibody responses to saliva of Triatoma infestans compared with animals placed in pre-existing control enclosures. Our results strongly suggest that insecticide-treated nets prevent triatomine bites and can thereby protect against infection with Trypanosoma cruzi. Anti-salivary immunoassays are powerful new tools to evaluate intervention strategies against Chagas disease.