Water-based interventions for schistosomiasis control

Abstract

Mass drug administration with praziquantel is the mainstay of programs for the control of schistosomiasis morbidity. However, there is a growing recognition that treatment alone will not be sufficient for eventually effecting elimination and that additional measures will be required to interrupt transmission. In the absence of a safe and an effective vaccine for human schistosomiasis, the strategies to reduce infection levels will necessarily involve some interventions that affect the water-related stages of the schistosome life cycle: by reducing exposure to infectious water, by moderating availability of the intermediate snail host, or by decreasing contamination of water with egg-containing excreta. While much research on the importance of water on schistosomiasis has been performed, advances in these areas have perhaps languished with the ready availability of a cost-effective treatment. As some endemic areas near a shift to an elimination goal, a better understanding of water-based interventions that can be used alone or in concert with treatment will be needed. Reinvigoration of laboratory, field, and human behavioral aspects of this research now will ensure that the appropriate strategies are available by the time their implementation becomes necessary.Keywords: Schistosomiasis, Control, Elimination, Water, Snail, Transmission.Schistosomiasis differs from most waterborne diseases in that rather than through ingestion of contaminated water, people become infected when their skin comes into contact with fresh water bodies that contain the parasite. As a result, strategies to purify collected drinking water that may be effective against other waterborne pathogens do not necessarily prevent transmission of schistosome infection as the act of collecting water, along with bathing, washing, swimming, and certain occupations can expose individuals to infection. More than 230 million people in the world are infected with one of the three major species of schistosomes: Schistosoma mansoni, Schistosoma japonicum, and Schistosoma haematobium, and more than 700 million people are at risk for infection in developing countries in Africa, Asia, and South America.

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

“…Looking to the future, treatment targets in the WHO 2020 Roadmap encourage further scale-up of PC campaigns but despite desirable features, drawbacks of MDA include the inactivity of PZQ against immature worms, the poor cure rates associated with singe treatments, the inability of treatment to guard against re-infection and the challenge of maintaining adequate treatment coverage in currently targeted groups [9, 11–15]. Extra efforts to maximise the impact of PC are well-discussed and ideally should be set within an integrated control strategy inclusive of: water, sanitation and hygiene (WASH) interventions, health education with behavioural change, environmental modification and snail control with focal mollusciciding [15–18], as highlighted by the World Health Assembly (WHA) in resolution WHA65.21. Whilst there are challenges ahead [13, 19], there is optimism grounded on epidemiological evidence and theory that elimination of schistosomiasis transmission in certain settings is achievable [14, 20–22].…”

Praziquantel for Schistosomiasis: Single-Drug Metabolism Revisited, Mode of Action, and Resistance

“…More than 200 million people are infected worldwide, and 600 million are at risk of infection (1,2). Control strategies have been employed to block transmission and reduce the disease burden, including mass and targeted chemotherapy, improvements to sanitation, modification of the environment, and the use of molluscicides (3,4). However, schistosomiasis remains a major public health problem, especially in rural regions of sub-Saharan Africa (2).…”

Something Old, Something New: is Praziquantel Enough for Schistosomiasis Control?

“…For persons with S. japonicum infection, annual MDA may not even be sufficient for morbidity control [5]. Improved interventions could include development and implementation of new treatment drugs or protective vaccines, more frequent treatment with praziquantel, or coupling treatment with interventions that interrupt the role cercaria-contaminated fresh water plays in transmission [12]. A great deal of effort has gone into identifying new compounds and vaccines for schistosomiasis and these efforts should continue.…”