The prevalence of onchocerciasis in Africa and Yemen, 2000–2018: a geospatial analysis
Authors: Schmidt Chris A. , Cromwell Elizabeth A. , Hill Elex , Donkers Katie M. , Schipp Megan F. , Johnson Kimberly B. , Pigott David M. ,   LBD 2019 Neglected Tropical Diseases Collaborators, Schmidt Chris A. , Cromwell Elizabeth A. , Hill Elex , Pigott David M. , Abbas Jaffar , Adekanmbi Victor , Adetokunboh Olatunji O. , Ahmed Muktar Beshir , Alanezi Fahad Mashhour , Alanzi Turki M. , Alipour Vahid , Andrei Catalina Liliana , Andrei Tudorel , Anvari Davood , Appiah Seth Christopher Yaw , Aqeel Muhammad , Arabloo Jalal , Jafarabadi Mohammad Asghari , Ausloos Marcel , Baig Atif Amin , Banach Maciej , Bärnighausen Till Winfried , Bhattacharyya Krittika , Bhutta Zulfiqar A. , Bijani Ali , Brady Oliver J. , Bragazzi Nicola Luigi , Butt Zahid A. , Carvalho Felix , Chattu Vijay Kumar , Dahlawi Saad M. A. , Damiani Giovanni , Demeke Feleke Mekonnen , Deribe Kebede , Dharmaratne Samath Dhamminda , Diaz Daniel , Didarloo Alireza , Earl Lucas , Zaki Maysaa El Sayed , El Tantawi Maha , Fattahi Nazir , Fernandes Eduarda , Foigt Nataliya A. , Foroutan Masoud , Franklin Richard Charles , Guo Yuming , Haj-Mirzaian Arvin , Hamidi Samer , Hassankhani Hadi , Herteliu Claudiu , Higazi Tarig B. , Hosseini Mostafa , Hosseinzadeh Mehdi , Househ Mowafa , Ilesanmi Olayinka Stephen , Ilic Irena M. , Ilic Milena D. , Irvani Seyed Sina Naghibi , Jha Ravi Prakash , Ji John S. , Jonas Jost B. , Jozwiak Jacek Jerzy , Kalankesh Leila R. , Kamyari Naser , Matin Behzad Karami , Karimi Salah Eddin , Kayode Gbenga A. , Karyani Ali Kazemi , Khan Ejaz Ahmad , Khan Md Nuruzzaman , Khatab Khaled , Khater Mona M. , Kianipour Neda , Kim Yun Jin , Kosen Soewarta , Kusuma Dian , La Vecchia Carlo , Lansingh Van Charles , Lee Paul H. , Li Shanshan , Maleki Shokofeh , Mansournia Mohammad Ali , Martins-Melo Francisco Rogerlândio , McAlinden Colm , Mendoza Walter , Mestrovic Tomislav , Moghadaszadeh Masoud , Mohammadian-Hafshejani Abdollah , Mohammadi Seyyede Momeneh , Mohammed Shafiu , Moradzadeh Rahmatollah , Moraga Paula , Naderi Mehdi , Nagarajan Ahamarshan Jayaraman , Negoi Ionut , Nguyen Cuong Tat , Nguyen Huong Lan Thi , Oancea Bogdan , Olagunju Andrew T. , Bali Ahmed Omar , Onwujekwe Obinna E. , Pana Adrian , Rahimi-Movaghar Vafa , Ramezanzadeh Kiana , Rawaf David Laith , Rawaf Salman , Rawassizadeh Reza , Rezapour Aziz , Ribeiro Ana Isabel , Samy Abdallah M. , Shaikh Masood Ali , Sharafi Kiomars , Sheikh Aziz , Singh Jasvinder A. , Skiadaresi Eirini , Soltani Shahin , Stolk Wilma A. , Sufiyan Mu’awiyyah Babale , Thomson Alan J. , Tran Bach Xuan , Tran Khanh Bao , Unnikrishnan Bhaskaran , Violante Francesco S. , Vu Giang Thu , Yamada Tomohide , Yaya Sanni , Yip Paul , Yonemoto Naohiro , Yu Chuanhua , Yu Yong , Zamanian Maryam , Zhang Yunquan , Zhang Zhi-Jiang , Ziapour Arash , Hay Simon I. , Hay Simon I. 
Published: September 2022

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.