Predicting the environmental suitability for onchocerciasis in Africa as an aid to elimination planning

Authors

Elizabeth A. Cromwell, University of Washington, Seattle, Washington, USA.
Joshua C P. Osborne, University of Washington, Seattle, Washington, USA.
Thomas R. Unnasch, University of South Florida, Tampa, Florida, USA.
Maria-Gloria Basáñez, Imperial College London, London, UK.
Katherine M. Gass, Neglected Tropical Diseases Support Center, Decatur, Georgia, USA.
Kira A. Barbre, Neglected Tropical Diseases Support Center, Decatur, Georgia, USA.
Elex Hill, University of Washington, Seattle, Washington, USA.
Kimberly B. Johnson, University of Washington, Seattle, Washington, USA.
Katie M. Donkers, University of Washington, Seattle, Washington, USA.
Zulfiqar Ahmed Bhutta, Aga Khan UniversityFollow

Document Type

Article

Department

Women and Child Health

Abstract

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.

Comments

Pagination are not provided by the author/publisher

Publication (Name of Journal)

PLoS Neglected Tropical Diseases

Recommended Citation

Cromwell, E. A., Osborne, J. P., Unnasch, T. R., Basáñez, M., Gass, K. M., Barbre, K. A., Hill, E., Johnson, K. B., Donkers, K. M., Bhutta, Z. A. (2021). Predicting the environmental suitability for onchocerciasis in Africa as an aid to elimination planning. PLoS Neglected Tropical Diseases, 15(7), e0008824.
Available at: https://ecommons.aku.edu/coe-wch/25

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.