What is required in terms of mass drug administration to interrupt the transmission of schistosome parasites in regions of endemic infection?
BACKGROUND
Schistosomiasis is endemic in 54 countries, but has one of the lowest coverages by mass drug administration of all helminth diseases. However, with increasing drug availability through donation, the World Health Organisation has set a goal of increasing coverage to 75 % of at-risk children in endemic countries and elimination in some regions. In this paper, we assess the impact on schistosomiasis of the WHO goals in terms of control and elimination.


METHODS
We use an age-structured deterministic model of schistosome transmission in a human community and the effect of mass drug administration. The model is fitted to baseline data from a longitudinal re-infection study in Kenya and validated against the subsequent re-infection data. We examine the impact on host worm burden of the current treatment trend, extrapolated to meet the WHO goals, and its sensitivity to uncertainty in important parameters. We assess the feasibility of achieving elimination.


RESULTS
Model results show that the current treatment trend, extrapolated to the WHO goals, is able to greatly reduce host worm burdens. If coverage is continued at the same level beyond 2020, elimination is possible for low to moderate transmission settings, where transmission intensity is defined by the basic reproduction number, R0. Low levels of adult coverage have a significant impact on worm burden in all settings. Model validation against the re-infection survey demonstrates that the age-structured model is able to match post-treatment data well in terms of egg output, but that some details of re-infection among school children and young adults are not currently well represented.


CONCLUSIONS
Our work suggests that the current WHO treatment goals should be successful in bringing about a major reduction in schistosome infection in treated communities. If continued over a 15 year period, they are likely to result in elimination, at least in areas with lower transmission.
London Centre for Neglected Tropical Disease Research, London, UK. roy.anderson@imperial.ac.uk.|Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK. roy.anderson@imperial.ac.uk.
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Anderson
London Centre for Neglected Tropical Disease Research, London, UK. hugo.turner@imperial.ac.uk.|Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK. hugo.turner@imperial.ac.uk.
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Turner
London Centre for Neglected Tropical Disease Research, London, UK. sam.farrell@imperial.ac.uk.|Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK. sam.farrell@imperial.ac.uk.
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Farrell
London Centre for Neglected Tropical Disease Research, London, UK. jie.yang1@imperial.ac.uk.|Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK. jie.yang1@imperial.ac.uk.
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Yang
London Centre for Neglected Tropical Disease Research, London, UK. j.truscott@imperial.ac.uk.|Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK. j.truscott@imperial.ac.uk.
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Truscott
D000871:Anthelmintics / Q000008:administration & dosage*; D060740:Disease Eradication; D018562:Disease Transmission, Infectious / Q000517:prevention & control*; D004358:Drug Therapy / Q000379:methods; D019353:Endemic Diseases; D006801:Humans; D008962:Models, Theoretical; D012552:Schistosomiasis / Q000188:drug therapy* / Q000453:epidemiology / Q000517:prevention & control*; D013997:Time Factors; D014944:World Health Organization
D000871:Anthelmintics