Long-term effect of mass chemotherapy of Schistosoma mansoni on infection rate and diagnosis accuracy

Objectives: To assess the performance of microscopic stool examination, which is used widely for the diagnosis and assessment of infection rates of Schistosoma mansoni in Egypt, for the evaluation of chemotherapy efficacy after a decade of regular mass treatment. Methods: A total of 651 individuals from Lower Egypt (55 children and 596 adults) were examined for S. mansoni ova by microscopic stool examination (MSE) alone (n = 166; 111 adults and 55 children), rectal biopsy (RB) alone (n = 32 adults), or both MSE and RB (n = 453 adults). Results: Infection detection rates were significantly lower in the MSE alone group (9%; 15/166) compared to the RB alone group (40.6%; 13/32) and to the RB+MSE group (37.7%; 171/453). Out of all positive cases in the MSE+RB group, only 23/171 patients (13.5%) were positive by stool examination, of whom 21 were also positive by RB, in contrast to 169/171 patients (86.5%) positive by RB in the same group. It was noted that adding MSE to RB did not increase the prevalence compared to RB alone: 37.3% in the MSE+RB group vs. 40.6% in the RB only group. Using the summation of both MSE and RB tests as the gold standard, the sensitivity of MSE was significantly lower than that of RB: 13.5% vs. 98.8%. Conclusions: The implementation of mass treatment programmes has resulted in a new era of light infection, for which conventional parasitological methods for the diagnosis and monitoring of infection can miss many patients