Adaptive strategies for schistosomiasis control
Authors: Mike French, Darin Evans
Journal: The Lancet Global Health (2019)

In this issue of The Lancet Global Health, Emily Li and colleagues1Li EY Gurarie D Lo NC Zhu X King CH Improving public health control of schistosomiasis with a modified WHO strategy: a model-based comparison study.Lancet Glob Health. 2019; 7: e1414-e1422Summary Full Text Full Text PDF PubMed Scopus (20) Google Scholar outline an innovative approach to adapting the current WHO schistosomiasis guidelines for morbidity control and elimination as a public health problem. The authors conclude that programmes can achieve their aims quicker if they undertake an early review of programme progress (after 2–3 years) and use the results to adapt their programmes. This adaptation can include increasing the frequency of praziquantel mass drug administration (MDA) and the possible addition of snail control. Li and colleagues found that this strategy led to larger decreases in prevalence over fewer rounds of MDA. Not only was it quicker but it was also more likely than the current guidelines to achieve morbidity control and elimination as a public health problem, particularly in high-risk areas. The proposal for a shorter interval from programme initiation to evaluation and modification than the 5–6 years currently recommended2WHOHelminth control in school-age children. A guide for managers of control programmes. World Health Organization, Geneva2011Google Scholar would allow the incorporation of empirical data more quickly and increase the use of data for decision making. Having this feedback loop to inform the treatment approach is important. Currently, there is some hesitancy among country programmes over doing impact assessments, as often the treatment approach does not subsequently change. As Li and colleagues identify, the time taken to achieve programmatic goals is not the only factor to be considered. The additional costs of increased MDA and impact surveys are also important, as is a better understanding of the transmission environment. To this we would add the logistical and planning complexities introduced by changing approach, especially in cases in which this might vary between neighbouring areas. Additional factors specific to snail control include community acceptance, environmental impact, and an incomplete evidence base. MDA alone is likely to reduce infection in most places, but infection will rebound in the absence of ongoing treatment. These programmes typically aim for long-term control rather than elimination of transmission; achieving elimination as a public health problem will require continued treatment, unlike for other neglected tropical diseases such as lymphatic filariasis and trachoma. Although the World Health Assembly 2012 resolution3WHOElimination of schistosomiasis.https://www.who.int/neglected_diseases/mediacentre/WHA_65.21_Eng.pdfDate: 2012Date accessed: August 27, 2019Google Scholar encourages countries to aim for transmission interruption, this goal is unlikely to be realistic in the short term in sub-Saharan Africa. In a 2018 paper,4French MD Evans D Fleming FM et al.Schistosomiasis in Africa: improving strategies for long-term and sustainable morbidity control.PLoS Negl Trop Dis. 2018; 12e0006484Crossref PubMed Scopus (22) Google Scholar we argued that elimination of transmission is a long-term aim requiring substantial socioeconomic development and systematic water and sanitation improvements. Aiming for morbidity control is an ambitious, probably achievable, and worthwhile goal. A relevant area requiring further study is the definition of schistosomiasis-related morbidity, which of course is crucial to define programme goals and to measure progress. Currently, morbidity is measured by a proxy: the proportion of people excreting a large number of eggs in the stool or urine. However, there is increasing recognition of morbidity in people excreting low numbers of eggs, and even those who do not excrete any eggs.5King CH Dickman K Tisch DJ Reassessment of the cost of chronic helmintic infection: a meta-analysis of disability-related outcomes in endemic schistosomiasis.Lancet. 2005; 365: 1561-1569Summary Full Text Full Text PDF PubMed Scopus (682) Google Scholar Furthermore, the management of chronic cases of morbidity is not addressed by MDA with praziquantel. We know that current prevalence estimates are probably substantially underestimated because of insensitive diagnostics. The development of the point-of-contact circulating cathodic antigen and circulating anodic antigen tests will help provide a more accurate estimate of the number of people infected who are potentially requiring treatment. As well as looking at new adaptive approaches, it is important that we continue to focus on aspects that can be effective immediately, such as high-quality programme implementation to ensure repeated rounds of high treatment coverage. In cases where this treatment coverage is not being achieved, quantitative and qualitative approaches should be used to understand the location-specific challenges. Likewise, accurately identifying the at-risk population is important. Most programmes focus primarily on children aged 5–14 years. Expanding treatment to adults, where required and where praziquantel is available, might be essential in reducing transmission and morbidity but will require accurate estimates of individuals at risk. The projected availability of a paediatric formulation of praziquantel will be another useful tool, given the increasing evidence of disease in this age-group.6Pediatric Praziquantel ConsortiumWhere we stand.https://www.pediatricpraziquantelconsortium.org/node/28Date: 2017Date accessed: August 27, 2019Google Scholar, 7Stothard JR Sousa-Figueiredo JC Betson M Bustinduy A Reinhard-Rupp J Schistosomiasis in African infants and preschool children: let them now be treated!.Trends Parasitol. 2013; 29: 197-205Summary Full Text Full Text PDF PubMed Scopus (120) Google Scholar We know that schistosomiasis infection is highly focal, often with substantial heterogeneity between neighbouring communities. Being better able to identify and respond to this focality and to persistent hotspots—ie, areas not responding as expected to treatment8Kittur N Binder S Campbell CH et al.Defining persistent hotspots: areas that fail to decrease meaningfully in prevalence after multiple years of mass drug administration with praziquantel for control of schistosomiasis.Am J Trop Med Hyg. 2017; 97: 1810-1817Crossref PubMed Scopus (54) Google Scholar, 9Wiegand RE Mwinzi PNM Montgomery SP et al.A persistent hotspot of Schistosoma mansoni infection in a five-year randomized trial of praziquantel preventative chemotherapy strategies.J Infect Dis. 2017; 216: 1425-1433Crossref PubMed Scopus (47) Google Scholar—requires new focused mapping approaches. Work to this end is being done by WHO, the Global Schistosomiasis Alliance, and partners. Finally, all of these discussed elements need to happen under the ownership of the government of the endemic country, led by their Ministry of Health. As Li and colleagues state, “it is crucial to design a sustainable control programme that can maintain government support, adequate funding, community involvement, [and] coordination between control programmes”. Countries need to take the lead in designing, implementing, and evaluating their own programmes. One approach to this management is the use of schistosomiasis (and soil-transmitted helminth) expert committees. The committees are created under the auspices of the Ministry of Health with input from domestic and international experts as required, modelled on the successful onchocerciasis elimination expert advisory groups.10Griswold E Unnasch T Eberhard M et al.The role of national committees in eliminating onchocerciasis.Int Health. 2018; 10: i60-i70Crossref PubMed Scopus (9) Google Scholar In this way, the capacity of the programme staff can be built to plan and adapt appropriately to the changing needs of the control programme. We declare no competing interests. Improving public health control of schistosomiasis with a modified WHO strategy: a model-based comparison studyThe modified adaptive decision making framework is predicted to be more effective than the current WHO guidelines in reaching 2025 public health goals, especially for high-prevalence regions. Modifications in current guidelines could reduce the time and resources needed for countries who are currently working on achieving public health goals against schistosomiasis. Full-Text PDF Open Access