Towards interruption of schistosomiasis transmission in sub-Saharan Africa:developing an appropriate environmental surveillance framework to guide and to support‘end game’interventions

Schistosomiasis is a waterborne parasitic disease in sub-Saharan Africa,particularly common in rural populations living in impoverished conditions.With the scale-up of preventive chemotherapy,national campaigns will transition from morbidity-to transmission-focused interventions thus formal investigation of actual or expected declines in environmental transmission is needed as‘end game’scenarios arise.Surprisingly,there are no international or national guidelines to do so in sub-Saharan Africa.Our article therefore provides an introduction to key practicalities and pitfalls in the development of an appropriate environmental surveillance framework.In this context,we discuss how strategies need to be adapted and tailored to the local level to better guide and support future interventions through this transition.As detection of egg-patent infection in people becomes rare,careful sampling of schistosome larvae in freshwater and in aquatic snails with robust species-specific DNA assays will be required.Appropriate metrics,derived from observed prevalence(s)as compared with predetermined thresholds,could each provide a clearer insight into contamination-and exposure-related dynamics.Application could be twofold,first to certify areas currently free from schistosomiasis transmission or second to red-flag recalcitrant locations where extra effort or alternative interventions are needed.

Performance of a real-time PCR approach for diagnosing Schistosoma haematobium infections of different intensity in urine samples from Zanzibar

Background:Efforts to control and eliminate schistosomiasis have accelerated over the past decade.As parasite burden,associated morbidity and egg excretion decrease,diagnosis with standard parasitological methods becomes harder.We assessed the robustness and performance of a real-time PCR(qPCR)approach in comparison with urine filtration microscopy and reagent strip testing for the diagnosis of Schistosoma haematobium infections of different intensities.Methods:The robustness of DNA isolation and qPCR was validated in eight laboratories from Europe and Africa.Subsequently,792 urine samples collected during cross-sectional surveys of the Zanzibar Elimination of Schistosomiasis Transmission(ZEST)project in 2012-2017 were examined with qPCR in 2018.Diagnostic sensitivity of the qPCR was calculated at different infection intensity categories,using urine filtration microscopy as reference test.Spearman's rank correlation between Ct-values and S.haematobium egg counts was assessed and Ct-value percentiles for infection intensity categories determined.Results:S.haematobium Dra1 DNA-positive samples were identified correctly in all eight laboratories.Examination of urine samples from Zanzibar revealed Dra1 DNA in 26.8%(212/792)by qPCR,S.haematobium eggs in 13.3%(105/792)by urine filtration,and microhaematuria in 13.8%(109/792)by reagent strips.Sensitivity of the qPCR increased with augmenting egg counts:80.6%(29/36)for counts between 1 and 4 eggs,83.3%(15/18)for counts between 5 and 9 eggs,100%(23/23)for counts between 10 and 49 eggs,and 96.4%(27/28)for counts of 50+eggs.There was a significant negative correlation between Ct-values and egg counts(Spearman's rho=-0.49,P<0.001).Seventy-five percent of the Ct-values were≥33 in the egg-negative category,<31 in the light intensity category,and<24 in the heavy intensity category.Conclusions:While the sensitiivity of the qPCR was^80%for very light intensity infections(egg counts<10),in general,the Dra1 based qPCR assay detected twice as many S.haematobium infections compared with classical parasitological tests.The qPCR is hence a sensitive,urine-based approach for S.haernatcbium diagnosis that can be used for impact assessment of schistosomiasis elimination programmes,individual diagnosis,and in improved format also for verification and certification of elimination.Trial registration:ISRCTN,ISRCTN48837681.Registered 05 September 2012-Retrospectively registered.