Controlling schistosomiasis: another reason why clean water is so important

By Dr Michael Templeton, Faculty of Engineering, Department of Civil and Environmental Engineering, Imperial College London

With World Water Day approaching on 22 March, research at Imperial College London is highlighting yet another example of why access to clean water is so vitally important to human health.

The research is seeking to quantify the role of access to clean water in reducing the odds of becoming infected with the neglected tropical disease schistosomiasis.

A schistosomiasis worm

It has been estimated that 200 million people in developing countries are infected with the parasite causing this disease, which manifests itself in a range of symptoms, including enlargement of the liver and spleen, anaemia, increased risk of bladder cancer, exacerbation of the transmission of HIV and its progression to AIDS, and in extreme cases seizures. The parasite lives within infected people, with aquatic snails acting as intermediate hosts and releasing cercariae (the larval form of the parasite) into water bodies, which then penetrate the skin of other people who come in contact with the contaminated water. Preventing people from coming into contact with contaminated water and preventing urine and faeces from passing into water bodies should stop this cycle, however most endemic countries lack adequate water and sanitation provision.

The World Health Assembly put forward an important resolution in 2012 to not only control but completely eliminate schistosomiasis, and it was recognised that this would require a multi-disciplinary strategy, involving mass preventive chemotherapy with the drug praziquantel but also improving access to water, sanitation and hygiene (WASH). Until the research at Imperial however, little evidence had been systematically collated and quantified regarding the role and effectiveness of WASH as part of schistosomiasis control.

A systematic review and meta-analysis was led by PhD student Jack Grimes, supervised by Dr Michael Templeton in the Department of Civil and Environmental Engineering and Dr Wendy Harrison of the Schistosomiasis Control Initiative (SCI) in the School of Public Health in the Faculty of Medicine, and with co-authors from the Swiss Tropical and Public Health Institute and Emory University, USA. The review considered 9,114 published studies and concluded that safe water supplies are associated with statistically significantly lower odds of schistosomiasis, for both Schistosomiasis mansoni (intestinal) and Schistosomiasis haematobium (urogenital).

Contact with contaminated water bodies typically takes place outside the home rather than at home, and the review highlighted that more research is needed into community-level WASH interventions rather than household-level provision. The review also summarised that most of the previous studies were observational and of mixed quality, with most being especially poor in terms of the definitions of access to safe water and improved sanitation, lack of details about the types and condition of WASH facilities available, and no rigorous comparison nor discussion of the possible differences in effectiveness of different WASH types with regard to schistosomiasis control specifically.  Socio-economic status was also recognised as an important confounding factor that needs to be taken into account by future randomised trials that seek to produce policy-relevant conclusions about the best WASH strategies for eliminating this neglected disease.

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