Predicting the environmental suitability for onchocerciasis in Africa as an aid to elimination planning
Authors: Cromwell Elizabeth A. , Osborne Joshua C. P. , Unnasch Thomas R. , Basáñez Maria-Gloria , Gass Katherine M. , Barbre Kira A. , Hill Elex , Johnson Kimberly B. , Donkers Katie M. , Shirude Shreya , Schmidt Chris A. , Adekanmbi Victor , Adetokunboh Olatunji O. , Afarideh Mohsen , Ahmadpour Ehsan , Ahmed Muktar Beshir , Akalu Temesgen Yihunie , Al-Aly Ziyad , Alanezi Fahad Mashhour , Alanzi Turki M. , Alipour Vahid , Andrei Catalina Liliana , Ansari Fereshteh , Ansha Mustafa Geleto , Anvari Davood , Appiah Seth Christopher Yaw , Arabloo Jalal , Arnold Benjamin F. , Ausloos Marcel , Ayanore Martin Amogre , Baig Atif Amin , Banach Maciej , Barac Aleksandra , Bärnighausen Till Winfried , Bayati Mohsen , Bhattacharyya Krittika , Bhutta Zulfiqar A. , Bibi Sadia , Bijani Ali , Bohlouli Somayeh , Bohluli Mahdi , Brady Oliver J. , Bragazzi Nicola Luigi , Butt Zahid A. , Carvalho Felix , Chatterjee Souranshu , Chattu Vijay Kumar , Chattu Soosanna Kumary , Cormier Natalie Maria , Dahlawi Saad M. A. , Damiani Giovanni , Daoud Farah , Darwesh Aso Mohammad , Daryani Ahmad , Deribe Kebede , Dharmaratne Samath Dhamminda , Diaz Daniel , Do Hoa Thi , El Sayed Zaki Maysaa , El Tantawi Maha , Elemineh Demelash Abewa , Faraj Anwar , Fasihi Harandi Majid , Fatahi Yousef , Feigin Valery L. , Fernandes Eduarda , Foigt Nataliya A. , Foroutan Masoud , Franklin Richard Charles , Gubari Mohammed Ibrahim Mohialdeen , Guido Davide , Guo Yuming , Haj-Mirzaian Arvin , Hamagharib Abdullah Kanaan , Hamidi Samer , Herteliu Claudiu , Hidru Hagos Degefa de , Higazi Tarig B. , Hossain Naznin , Hosseinzadeh Mehdi , Househ Mowafa , Ilesanmi Olayinka Stephen , Ilic Milena D. , Ilic Irena M. , Iqbal Usman , Irvani Seyed Sina Naghibi , Jha Ravi Prakash , Joukar Farahnaz , Jozwiak Jacek Jerzy , Kabir Zubair , Kalankesh Leila R. , Kalhor Rohollah , Karami Matin Behzad , Karimi Salah Eddin , Kasaeian Amir , Kavetskyy Taras , Kayode Gbenga A. , Kazemi Karyani Ali , Kelbore Abraham Getachew , Keramati Maryam , Khalilov Rovshan , Khan Ejaz Ahmad , Khan Md Nuruzzaman Nuruzzaman , Khatab Khaled , Khater Mona M. , Kianipour Neda , Kibret Kelemu Tilahun , Kim Yun Jin , Kosen Soewarta , Krohn Kris J. , Kusuma Dian , La Vecchia Carlo , Lansingh Van Charles , Lee Paul H. , LeGrand Kate E. , Li Shanshan , Longbottom Joshua , Magdy Abd El Razek Hassan , Magdy Abd El Razek Muhammed , Maleki Afshin , Mamun Abdullah A. , Manafi Ali , Manafi Navid , Mansournia Mohammad Ali , Martins-Melo Francisco Rogerlândio , Mazidi Mohsen , McAlinden Colm , Meharie Birhanu Geta , Mendoza Walter , Mengesha Endalkachew Worku , Mengistu Desalegn Tadese , Mereta Seid Tiku , Mestrovic Tomislav , Miller Ted R. , Miri Mohammad , Moghadaszadeh Masoud , Mohammadian-Hafshejani Abdollah , Mohammadpourhodki Reza , Mohammed Shafiu , Mohammed Salahuddin , Moradi Masoud , Moradzadeh Rahmatollah , Moraga Paula , Mosser Jonathan F. , Naderi Mehdi , Nagarajan Ahamarshan Jayaraman , Naik Gurudatta , Negoi Ionut , Nguyen Cuong Tat , Nguyen Huong Lan Thi , Nguyen Trang Huyen , Nikbakhsh Rajan , Oancea Bogdan , Olagunju Tinuke O. , Olagunju Andrew T. , Omar Bali Ahmed , Onwujekwe Obinna E. , Pana Adrian , Pourjafar Hadi , Rahim Fakher , Rahman Mohammad Hifz Ur , Rathi Priya , Rawaf Salman , Rawaf David Laith , Rawassizadeh Reza , Resnikoff Serge , Reta Melese Abate , Rezapour Aziz , Rubagotti Enrico , Rubino Salvatore , Sadeghi Ehsan , Saghafipour Abedin , Sajadi S. Mohammad , Samy Abdallah M. , Sarmiento-Suárez Rodrigo , Sawhney Monika , Schipp Megan F. , Shaheen Amira A. , Shaikh Masood Ali , Shamsizadeh Morteza , Sharafi Kiomars , Sheikh Aziz , Shetty B. Suresh Kumar , Shin Jae Il , Shivakumar K. M. , Simonetti Biagio , Singh Jasvinder A. , Skiadaresi Eirini , Soheili Amin , Soltani Shahin , Spurlock Emma Elizabeth , Sufiyan Mu’awiyyah Babale , Tabuchi Takahiro , Tapak Leili , Thompson Robert L. , Thomson Alan J. , Traini Eugenio , Tran Bach Xuan , Ullah Irfan , Ullah Saif , Uneke Chigozie Jesse , Unnikrishnan Bhaskaran , Uthman Olalekan A. , Vinkeles Melchers Natalie V. S. , Violante Francesco S. , Wolde Haileab Fekadu , Wonde Tewodros Eshete , Yamada Tomohide , Yaya Sanni , Yazdi-Feyzabadi Vahid , Yip Paul , Yonemoto Naohiro , Yousof Hebat-Allah Salah A. , Yu Chuanhua , Yu Yong , Yusefzadeh Hasan , Zaki Leila , Zaman Sojib Bin , Zamanian Maryam , Zhang Zhi-Jiang , Zhang Yunquan , Ziapour Arash , Hay Simon I. , Pigott David M. 
Published: July 2021

Recent evidence suggests that, in some foci, elimination of onchocerciasis from Africa may be feasible with mass drug administration (MDA) of ivermectin. To achieve continental elimination of transmission, mapping surveys will need to be conducted across all implementation units (IUs) for which endemicity status is currently unknown. Using boosted regression tree models with optimised hyperparameter selection, we estimated environmental suitability for onchocerciasis at the 5 × 5-km resolution across Africa. In order to classify IUs that include locations that are environmentally suitable, we used receiver operating characteristic (ROC) analysis to identify an optimal threshold for suitability concordant with locations where onchocerciasis has been previously detected. This threshold value was then used to classify IUs (more suitable or less suitable) based on the location within the IU with the largest mean prediction. Mean estimates of environmental suitability suggest large areas across West and Central Africa, as well as focal areas of East Africa, are suitable for onchocerciasis transmission, consistent with the presence of current control and elimination of transmission efforts. The ROC analysis identified a mean environmental suitability index of 0·71 as a threshold to classify based on the location with the largest mean prediction within the IU. Of the IUs considered for mapping surveys, 50·2% exceed this threshold for suitability in at least one 5 × 5-km location. The formidable scale of data collection required to map onchocerciasis endemicity across the African continent presents an opportunity to use spatial data to identify areas likely to be suitable for onchocerciasis transmission. National onchocerciasis elimination programmes may wish to consider prioritising these IUs for mapping surveys as human resources, laboratory capacity, and programmatic schedules may constrain survey implementation, and possibly delaying MDA initiation in areas that would ultimately qualify.