Participatory integrated control strategies and elimination of schistosomiasis in sub-Saharan Africa
Authors: Humphrey D Mazigo
Journal: The Lancet Global Health (2019)

Sub-Saharan Africa is home to 95% of the 250 million people estimated to be infected with schistosomiasis.1Colley DG Bustinduy AL Secor WE King CH Human schistosomiasis.Lancet. 2014; 383: 2253-2264Summary Full Text Full Text PDF PubMed Scopus (1444) Google Scholar, 2Rollinson D Knopp S Levitz S et al.Time to set the agenda for schistosomiasis elimination.Acta Trop. 2013; 128: 423-440Crossref PubMed Scopus (386) Google Scholar In the region, schistosomiasis affects the poorest communities characterised by insufficient supply of clean water and poor access to adequate sanitation.1Colley DG Bustinduy AL Secor WE King CH Human schistosomiasis.Lancet. 2014; 383: 2253-2264Summary Full Text Full Text PDF PubMed Scopus (1444) Google Scholar, 3Hotez PJ Kamath A Neglected tropical diseases in sub-saharan Africa: review of their prevalence, distribution, and disease burden.PLoS Neg Trop Dis. 2009; 3: e412Crossref PubMed Scopus (756) Google Scholar Mass drug administration (MDA) with the antischistosome drug praziquantel (PZQ) is the only control measure implemented against schistosomiasis in most of sub-Saharan Africa.4WHOSchistosomiasis: progress report 2001–2011, strategic plan 2012–2020. World Health Organization, Geneva2013https://www.who.int/schistosomiasis/resources/9789241503174/en/Date accessed: June 17, 2019Google Scholar Commendable work has been done in scaling up the distribution of PZQ, with dramatic increases in the number of people treated from 7 million in 2006 to over 57 million people in 2015.5Wold Health OrganizationSummary of global update on preventive chemotherapy implementation in 2015.Wkly Epidemiol Rec. 2016; 91: 456-460PubMed Google Scholar However, critics of this approach note that preventive chemotherapy with PZQ alone is unlikely to control, let alone eliminate schistosomiasis.6Fenwick A Jourdan P Schistosomiasis elimination by 2020 or 2030?.Int J Parasitol. 2016; 46: 385-388Crossref PubMed Scopus (32) Google Scholar Considering this, in 2012, WHO published the neglected tropical diseases Roadmap for 2012–2025 and in the same year, WHO member states endorsed the WHA65.21 resolution on elimination of schistosomiasis.7WHOResolution WHA65.21. Elimination of schistosomiasis. Sixty-Fifth World Health Assembly. World Health Organization, Geneva2012Google Scholar This resolution has emphasised the continuum from control, to elimination, to eradication of schistosomiasis. Moving from control to elimination requires changes in the strategies of MDA with PZQ to inclusion of complementary measures.8Tchuem Tchuente LA. Rollinson D. Stothard J Molyneux D Moving from control to elimination of schistosomiasis in sub-Saharan Africa: time to change and adapt strategies.Infect Dis Poverty. 2017; 6: 42Crossref PubMed Scopus (103) Google Scholar Integrated intervention measures including public health education, access to clean water, improved sanitation, and snail control are highly recommended in this paradigm shift from control to elimination.6Fenwick A Jourdan P Schistosomiasis elimination by 2020 or 2030?.Int J Parasitol. 2016; 46: 385-388Crossref PubMed Scopus (32) Google Scholar, 8Tchuem Tchuente LA. Rollinson D. Stothard J Molyneux D Moving from control to elimination of schistosomiasis in sub-Saharan Africa: time to change and adapt strategies.Infect Dis Poverty. 2017; 6: 42Crossref PubMed Scopus (103) Google Scholar A combination of these intervention measures can interrupt the lifecycle of the parasite. It is worth noting that, despite these recommendations, integration of these measures into MDA programmes in the sub-Saharan African environment has not been conclusively tested before. In this issue of Lancet Global Health, Knopp and colleagues' cluster randomised trial provides programmatic insight on how to implement integrated interventions with the goal of elimination of Schistosoma haematobium infection in an African setting with low prevalence (ranging from 4·2%–7·8%).9Knopp S Person B Ame SM et al.Evaluation of integrated interventions layered on mass drug administration for urogenital schistosomiasis elimination: a cluster-randomised trial.Lancet Glob Health. 2019; (published online June 26.)http://dx.doi.org/10.1016/S2214-109X(19)30189-5Scopus (47) Google Scholar The study, done in Zanzibar, assessed the efficacy of three intervention strategies: biannual MDA with PZQ alone, biannual MDA in combination with snail control, or biannual MDA with PZQ and activities to promote behaviour change. The primary outcome was S haematobium prevalence and infection intensity after 5 years of follow-up in schoolchildren. At the end of 5 years, the overall prevalence of S haematobium infection was 1·7% and of heavy infections was 0·4%, with no significant difference between intervention arms (arm 2 and arm 1 [1·7% vs 1·4%, odds ratio (OR) 1·2, 95%CI 0·6–2·7]; arm 3 and arm 1 [1·9% vs 1·4%, OR 1·3, 95% CI 0·6–2·9]). Several interpretations and conclusions can be drawn from these results. Based on the results, a significant decline in the prevalence of S haematobium can be expected with biannual MDA with PZQ for 5 years without integrating other complementary measures in an area with a relatively low baseline prevalence of S haematobium. Partly, the strong effect of PZQ might have masked the effects of other integrated measures such as mollusciciding and behavioural change activities on the outcome of interest. In addition, the effects of behavioural changes on prevalence and infection intensity of S haematobium takes time and the period of 5 years focusing only on schoolchildren was probably not enough. Similarly, to see the effects of molluscicide application on the prevalence and infection intensity, the intervention must cover a large area with potential breeding sites of intermediate host snails that is habitually frequented by the human population. Knopp and colleagues' study covered only water bodies in which snails were identified after scooping, whereas those that had no snails were not sprayed with molluscicides. The limitations of the scooping method to collect snails from water bodies with a low density of snails must be acknowledged. This might have resulted in misclassification of snail breeding sites and allowed transmission of S haematobium to continue from water bodies which were incorrectly defined to have no snails, yet are accessed by the human population. In addition, the ecology of Unguja island supports sugarcane and rice farming, and these wet farmland areas are potential breeding sites for the snail intermediate hosts that were not considered for molluscicide treatment. A more thorough application of molluscicides to all water bodies and farmlands might have allowed the molluscicide trial arm to more closely approach elimination. The authors have described several limitations and challenges during implementation and evaluation of the project. These are good lessons and stepping stones for future implementation of similar activities in a sub-Saharan African setting. A crucial learning point from this trial is the need for a bottom-up approach rather than a top-down approach when implementing community based public health interventions. Involvement of the targeted community during planning and addressing community needs in the context of schistosomiasis control will ensure sustainability and community ownership of the interventions. The failure to use and maintain urinals by the communities is possibly owing to the investigators' use of a top-down approach. Control of schistosomiasis in sub-Saharan Africa is a long-term project and moving from control to elimination will require policy changes, modifications, and changes in strategies from the MDA approach alone to an integrated approach. Intensified treatment with PZQ covering all age groups and hard to reach communities, implementation of complementary public health measures, such as improved access to clean water and sanitation, and interventions to promote behavioural changes are required to reach the elimination goals. The need for new diagnostic tests to help in defining elimination should also be part of the agenda. In general, for the integrated approach to have meaningful effect, political support and community engagement will be essential. Multisectoral approaches should form a central pillar of moving from control to elimination of schistosomiasis in sub-Saharan Africa. I declare no competing interests. Evaluation of integrated interventions layered on mass drug administration for urogenital schistosomiasis elimination: a cluster-randomised trialBiannual MDA substantially reduced the S haematobium prevalence and infection intensity but was insufficient to interrupt transmission. Although snail control or behaviour change activities did not significantly boost the effect of MDA in our study, they might enhance interruption of transmission when tailored to focal endemicity and applied for a longer period. It is now necessary to focus on reducing prevalence in remaining hotspot areas and to introduce new methods of surveillance and public health response so that the important gains can be maintained and advanced. Full-Text PDF Open Access