Comparison of three real-time polymerase chain reaction protocols for the diagnosis of imported schistosomiasis in a non-endemic setting.

Abstract

Background: Schistosomiasis is a neglected tropical disease that mostly affects inhabitants of sub-Saharan Africa. With rising global migration, imported cases of schistosomiasis are increasingly being reported in non-endemic countries, where diagnosis is hindered by low parasite burdens and multiple Schistosoma species. Microscopy remains the gold standard, despite its limitations, whereas molecular techniques offer greater sensitivity. The aim of this study was to assess the performance of real-time polymerase chain reaction (PCR) protocols for the detection, at an international health centre in Barcelona, of imported cases of urogenital and intestinal schistosomiasis. Methods: This cross-sectional study included 75 adults from sub-Saharan Africa attending the Drassanes-Vall d'Hebron International Health Unit, Barcelona, between May 2023 and February 2024. Paired urine and stool samples were collected. Microscopy was performed on all samples. Urine was analysed by real-time PCR using the Dra1 target sequence. Stool was tested by three protocols targeting, respectively, Dra1, Sm1-7, and 28S rRNA. Schistosoma infection was confirmed by microscopic identification of eggs and/or parasite DNA detection by real-time PCR. Results: Schistosomiasis was confirmed in 12/75 patients (16%). Urogenital schistosomiasis was diagnosed in 3/75 cases; the performance values of real-time PCR in urine samples were not assessed. In stool, the pan-Schistosoma real-time PCR showed 55.6% sensitivity and 98.5% specificity, with a moderate agreement (κ = 0.631) with microscopy. The Sm1-7 assay fully matched microscopy for Schistosoma mansoni detection, and reached 100% sensitivity and specificity. A novel contribution of this study is the application of a real-time PCR assay targeting the Dra1 repetitive sequence in stool samples for the detection of Schistosoma intercalatum/Schistosoma guineensis. All of the microscopy-positive cases were real-time PCR positive, and one additional infection was detected by real-time PCR, which meant that 100% sensitivity and 98.6% specificity were achieved with this technique. Conclusions: Our findings underscore the need for accurate diagnostic tools for cases of imported schistosomiasis in non-endemic settings. Microscopy remains the reference standard, while the pan-Schistosoma real-time PCR showed limited sensitivity for stool samples. In contrast, the Sm1-7 and Dra1 assays demonstrated higher sensitivity and strong concordance with microscopy, with Dra1 also proving useful for the detection of S. intercalatum/S. guineensis in stool.