Modelling control of Schistosoma haematobium infection: predictions of the long-term impact of mass drug administration in Africa.
BACKGROUND
Effective control of schistosomiasis remains a challenging problem for endemic areas of the world. Given knowledge of the biology of transmission and past experience with mass drug administration (MDA) programs, it is important to critically evaluate the likelihood that MDA programs will achieve substantial reductions in Schistosoma prevalence. In implementing the World Health Organization Roadmap for Neglected Tropical Diseases it would useful for policymaking to model projections of the status of Schistosoma control in MDA-treated areas in the next 5-10 years.


METHODS
Calibrated mathematical models were used to project the effects of different frequency and coverage of MDA for schistosomiasis haematobia control in present-day endemic communities, taking into account uncertainties of parasite biology and input data. The modeling approach in this analysis was the Stratified Worm Burden model developed in our earlier works, calibrated using data from longitudinal S. haematobium control trials in Kenya.


RESULTS
Model-based simulations of MDA control in typical low-risk and higher-risk communities indicated that infection prevalence can be substantially reduced within 10 years only when there is a high degree of community participation (>70 %) with at least annual MDA. Significant risk for re-emergence of infection remains if MDA is suspended.


CONCLUSIONS
In a stable (stationary) ecosystem, Schistosoma reproduction and transmission are sufficiently robust that the process of human infection continues, even under pressure from aggressive MDA. MDA alone is unlikely to interrupt transmission, and once mass treatment is suspended, the prevalence of human infection is likely to rebound to pre-control levels over a period of 25-30 years. MDA success in achieving very low levels of infection prevalence is highly dependent on treatment coverage and frequency within the local human population, and requires that both adults and children be included in drug delivery coverage. Ultimately, supplemental snail control and significant improvements in sanitation will be required to achieve full control of schistosomiasis by elimination of ongoing Schistosoma transmission.
Department of Mathematics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio, USA. dxg5@case.edu.
David
D
Gurarie
Department of Mathematics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio, USA. nxy47@case.edu.
Nara
N
Yoon
Center for Global Health and Diseases, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio, USA. yel3@case.edu.
Emily
E
Li
Department of Epidemiology, Yale School of Public Health, 60 College Street, New Haven, Connecticut, USA. martial.ndeffo-mbah@yale.edu.
Martial
M
Ndeffo-Mbah
Department of Epidemiology, Yale School of Public Health, 60 College Street, New Haven, Connecticut, USA. david.durham@yale.edu.
David
D
Durham
Schistosomiasis Control Initiative, Imperial College, Norfolk Place, St Mary's Campus, London, UK. a.phillips05@imperial.ac.uk.
Anna E
AE
Phillips
Schistosomiasis Control Initiative, Imperial College, Norfolk Place, St Mary's Campus, London, UK. valdoaurelio1@yahoo.com.br.
H Osvaldo
HO
Aurelio
Universidade Catholica de Moçambique, Beira, Mozambique. josefoferro@yahoo.com.br.
Josefo
J
Ferro
Department of Epidemiology, Yale School of Public Health, 60 College Street, New Haven, Connecticut, USA. alison.galvani@yale.edu.
Alison P
AP
Galvani
Center for Global Health and Diseases, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio, USA. chk@cwru.edu.|Schistosomiasis Consortium for Operational Research and Evaluation, University of Georgia, Athens, Georgia, USA. chk@cwru.edu.
Charles H
CH
King
D000328:Adult; D000349:Africa; D000818:Animals; D000871:Anthelmintics / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D011223:Praziquantel / Q000008:administration & dosage*; D012548:Schistosoma haematobium / Q000187:drug effects* / Q000502:physiology; D012553:Schistosomiasis haematobia / Q000188:drug therapy / Q000469:parasitology / Q000517:prevention & control*; D013997:Time Factors
D000871:Anthelmintics; D011223:Praziquantel