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. 2022 Sep 7;20(1):293.
doi: 10.1186/s12916-022-02486-y.

The prevalence of onchocerciasis in Africa and Yemen, 2000-2018: a geospatial analysis

Chris A Schmidt  1 , Elizabeth A Cromwell  2 , Elex Hill  2 , Katie M Donkers  2 , Megan F Schipp  2 , Kimberly B Johnson  2 , David M Pigott  2 ; LBD 2019 Neglected Tropical Diseases Collaborators; Simon I Hay  2
Collaborators, Affiliations

The prevalence of onchocerciasis in Africa and Yemen, 2000-2018: a geospatial analysis

Chris A Schmidt et al. BMC Med. .

Abstract

Background: Onchocerciasis is a disease caused by infection with Onchocerca volvulus, which is transmitted to humans via the bite of several species of black fly, and is responsible for permanent blindness or vision loss, as well as severe skin disease. Predominantly endemic in parts of Africa and Yemen, preventive chemotherapy with mass drug administration of ivermectin is the primary intervention recommended for the elimination of its transmission.

Methods: A dataset of 18,116 geo-referenced prevalence survey datapoints was used to model annual 2000-2018 infection prevalence in Africa and Yemen. Using Bayesian model-based geostatistics, we generated spatially continuous estimates of all-age 2000-2018 onchocerciasis infection prevalence at the 5 × 5-km resolution as well as aggregations to the national level, along with corresponding estimates of the uncertainty in these predictions.

Results: As of 2018, the prevalence of onchocerciasis infection continues to be concentrated across central and western Africa, with the highest mean estimates at the national level in Ghana (12.2%, 95% uncertainty interval [UI] 5.0-22.7). Mean estimates exceed 5% infection prevalence at the national level for Cameroon, Central African Republic, Democratic Republic of the Congo (DRC), Guinea-Bissau, Sierra Leone, and South Sudan.

Conclusions: Our analysis suggests that onchocerciasis infection has declined over the last two decades throughout western and central Africa. Focal areas of Angola, Cameroon, the Democratic Republic of the Congo, Ethiopia, Ghana, Guinea, Mali, Nigeria, South Sudan, and Uganda continue to have mean microfiladermia prevalence estimates exceeding 25%. At and above this level, the continuation or initiation of mass drug administration with ivermectin is supported. If national programs aim to eliminate onchocerciasis infection, additional surveillance or supervision of areas of predicted high prevalence would be warranted to ensure sufficiently high coverage of program interventions.

Keywords: Geospatial model; Neglected tropical diseases; Onchocerciasis.

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Conflict of interest statement

M Ausloos reports grants or contracts from the Romanian National Authority for Scientific Research and Innovation, CNDS-UEFISCDI (research grant (oct 2018-sep 2022); role: team leader (Bucharest University of Economic Studies); grant title “Understanding and modelling time-space patterns of psychology-related inequalities and polarization”), outside the submitted work. T Bärnighausen reports research grants from the European Union (Horizon 2020 and EIT Health), German Research Foundation (DFG), US National Institutes of Health, German Ministry of Education and Research, Alexander von Humboldt Foundation, Else-Kröner-Fresenius-Foundation, Wellcome Trust, Bill & Melinda Gates Foundation, KfW, UNAIDS, and WHO; consulting fees from KfW for the OSCAR initiative in Vietnam; participation on a Data Safety Monitoring Board or Advisory Board with NIH-funded study “Healthy Options” (PIs: Smith Fawzi, Kaaya), Chair, Data Safety and Monitoring Board (DSMB), German National Committee on the “Future of Public Health Research and Education”, Chair of the scientific advisory board to the EDCTP Evaluation, Member of the UNAIDS Evaluation Expert Advisory Committee, National Institutes of Health Study Section Member on Population and Public Health Approaches to HIV/AIDS (PPAH), US National Academies of Sciences, Engineering, and Medicine’s Committee for the “Evaluation of Human Resources for Health in the Republic of Rwanda under the President’s Emergency Plan for AIDS Relief (PEPFAR)”, University of Pennsylvania (UPenn) Population Aging Research Center (PARC) External Advisory Board Member; leadership role of the Global Health Hub Germany (initiated by the German Ministry of Health) as a co-chair; all outside the submitted work. R C Franklin reports a leadership or fiduciary role in board, society, committee or advocacy group, paid or unpaid, with the Australasian College of Tropical Medicine as the Honorary Treasurer and Vice President; outside the submitted work. C Herteliu and A Pana report grants or contracts from Romanian National Authority for Scientific Research and Innovation, CNDS-UEFISCDI, project number PN-III-P4-ID-PCCF-2016-0084 (oct 2018-sep 2022) “Understanding and modelling time-space patterns of psychology-related inequalities and polarization” and project number PN-III-P2-2.1-SOL-2020-2-0351 (jun 2020-oct 2020) “Approaches within public health management in the context of COVID-19 pandemic”, all outside the submitted work. J S Ji reports consulting fees paid directly from The World Bank Group; honoraria from the Chinese Preventive Medicine Association and China Center for Disease Control and Prevention National Institute of Environmental Health Science, outside the submitted work. J Jozwiak reports payments from Teva Pharmaceuticals, Amgen, Synexus, Boehringer Ingelheim, ALAB laboratoria, and Zentiva as personal fees outside the submitted work. A Sheikh reports a research grant to their institutions from Health Data Research UK outside the submitted work. J A Singh reports consulting fees from Crealta/Horizon, Medisys, Fidia, PK Med, Two labs Inc., Adept Field Solutions, Clinical Care options, Clearview healthcare partners, Putnam associates, Focus forward, Navigant consulting, Spherix, MedIQ, Jupiter Life Science, UBM LLC, Trio Health, Medscape, WebMD, and Practice Point communications; and the National Institutes of Health and the American College of Rheumatology; payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from Simply Speaking; support for attending meetings and/or travel from OMERACT, an international organization that develops measures for clinical trials and receives arm’s length funding from 12 pharmaceutical companies, when traveling to OMERACT meetings; participation on a Data Safety Monitoring Board or Advisory Board as a member of the FDA Arthritis Advisory Committee; leadership or fiduciary role in other board, society, committee or advocacy group, paid or unpaid, with OMERACT as a member of the steering committee, with the Veterans Affairs Rheumatology Field Advisory Committee as a member, and with the UAB Cochrane Musculoskeletal Group Satellite Center on Network Meta-analysis as a director and editor; stock or stock options in TPT Global Tech, Vaxart pharmaceuticals, Atyu Biopharma, Adaptimmune Therapeutics, GeoVax Labs, Pieris Pharmaceuticals, Enzolytics, Inc., Seres Therapeutics and Charlotte’s Web Holdings Inc. and previously owned stock options in Amarin, Viking, and Moderna pharmaceuticals; all outside the submitted work. W A Stolk reports grants or contracts from the Bill and Melinda Gates Foundation (BMGF) as an active member of the NTD Modelling Consortium (grant number OPP1184344); consulting fees from Mectizan Donation Programme as a member of the Mectizan Expert Committee (MEC) in the form of a small honorarium for participating in MEC meetings; all outside the submitted work. All other authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Prevalence of O. volvulus microfiladermia in Africa and Yemen at the 5 × 5-km level. Mean predictions of O. volvulus microfiladermia prevalence (all-age, both sexes) from the Bayesian geostatistical model, as measured by skin snip biopsies and crosswalked nodule palpation surveys. Hatch-marks indicate countries for which estimates were not produced; grey areas are masked based on sparsely populated areas (fewer than ten people per 1 × 1-km grid cell) and barren landscape classification. Data can be viewed on an interactive visualization tool at https://vizhub.healthdata.org/lbd/oncho
Fig. 2
Fig. 2
Africa and Yemen O. volvulus microfiladermia model uncertainty at the 5 x 5-km level. Mean and absolute uncertainty (measured as the range, or difference between, the upper and lower 95% UI) in O. volvulus microfiladermia prevalence estimates (all-age, both sexes) in Africa and Yemen. Hatch-marks indicate countries for which estimates were not produced; grey areas are masked based on sparsely populated areas (fewer than ten people per 1 × 1-km grid cell) and barren landscape classification. Quantile breakpoints for plotted categories are 0.001 (25th percentile), 0.009 (50th percentile), and 0.048 (75th percentile) for mean prevalence, and 0.009, 0.054, and 0.258 for range. Data can be viewed on an interactive visualization tool at https://vizhub.healthdata.org/lbd/oncho.
Fig. 3
Fig. 3
Distribution of onchocerciasis prevalence within and among countries at administrative level 2 (2000 and 2018). The median (central points) and lowest–highest (bars) mean prevalence estimates at administrative level 2 are shown for each country in the modeling region, for 2000 and 2018. Countries are ordered by increasing median administrative level 2 prevalence in 2018
See this image and copyright information in PMC

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