title: Modelling the elimination of river blindness using long-term epidemiological and programmatic data from Mali and Senegal.
abstract: The onchocerciasis transmission models EPIONCHO and ONCHOSIM have been independently developed and used to explore the feasibility of eliminating onchocerciasis from Africa with mass (annual or biannual) distribution of ivermectin within the timeframes proposed by the World Health Organization (WHO) and endorsed by the 2012 London Declaration on Neglected Tropical Diseases (i.e. by 2020/2025). Based on the findings of our previous model comparison, we implemented technical refinements and tested the projections of EPIONCHO and ONCHOSIM against long-term epidemiological data from two West African transmission foci in Mali and Senegal where the observed prevalence of infection was brought to zero circa 2007-2009 after 15-17 years of mass ivermectin treatment. We simulated these interventions using programmatic information on the frequency and coverage of mass treatments and trained the model projections using longitudinal parasitological data from 27 communities, evaluating the projected outcome of elimination (local parasite extinction) or resurgence. We found that EPIONCHO and ONCHOSIM captured adequately the epidemiological trends during mass treatment but that resurgence, while never predicted by ONCHOSIM, was predicted by EPIONCHO in some communities with the highest (inferred) vector biting rates and associated pre-intervention endemicities. Resurgence can be extremely protracted such that low (microfilarial) prevalence between 1% and 5% can be maintained for 3-5 years before manifesting more prominently. We highlight that post-treatment and post-elimination surveillance protocols must be implemented for long enough and with high enough sensitivity to detect possible residual latent infections potentially indicative of resurgence. We also discuss uncertainty and differences between EPIONCHO and ONCHOSIM projections, the potential importance of vector control in high-transmission settings as a complementary intervention strategy, and the short remaining timeline for African countries to be ready to stop treatment safely and begin surveillance in order to meet the impending 2020/2025 elimination targets.
authors.affiliation: Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research, Imperial College London, Norfolk Place, W2 1 PG, London, UK; Department of Pathobiology and Population Sciences and London Centre for Neglected Tropical Disease Research, Royal Veterinary College, Hawkshead Lane, Hatfield, AL9 7TA, UK. Electronic address: m.walker06@imperial.ac.uk.
authors.forename: Martin
authors.initials: M
authors.lastname: Walker
authors.affiliation: Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands.
authors.forename: Wilma A
authors.initials: WA
authors.lastname: Stolk
authors.affiliation: Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands; MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, Keppel Street, London, UK; Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research, Imperial College London, Norfolk Place, W2 1 PG, London, UK.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Dixon
authors.affiliation: Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands; MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, Keppel Street, London, UK.
authors.forename: Christian
authors.initials: C
authors.lastname: Bottomley
authors.affiliation: Inter-Country Support Team for West Africa, World Health Organization 158, Place de l'Indépendance 03 BP 7019, Ouagadougou 03, Burkina Faso.
authors.forename: Lamine
authors.initials: L
authors.lastname: Diawara
authors.affiliation: Programme National de Lutte contre l'Onchocercose (PNLO), Direction Nationale de la Santé (DNS), B.P. 233, Bamako, Mali.
authors.forename: Mamadou O
authors.initials: MO
authors.lastname: Traoré
authors.affiliation: Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands.
authors.forename: Sake J
authors.initials: SJ
authors.lastname: de Vlas
authors.affiliation: Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands; MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, Keppel Street, London, UK; Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research, Imperial College London, Norfolk Place, W2 1 PG, London, UK.
authors.forename: María-Gloria
authors.initials: MG
authors.lastname: Basáñez
mesh_terms: D006801:Humans; D007559:Ivermectin / Q000627:therapeutic use*; D008302:Mali / Q000453:epidemiology; D015827:Onchocerciasis, Ocular / Q000453:epidemiology* / Q000517:prevention & control* / Q000635:transmission; D015995:Prevalence; D012675:Senegal / Q000453:epidemiology
chemical_list: D007559:Ivermectin
keywords: Elimination; Mathematical modelling; Onchocerciasis; River blindness; Surveillance