Mapping suitability for Buruli ulcer at fine spatial scales across Africa: A modelling study

Abstract

Buruli ulcer (BU) is a disabling and stigmatising neglected tropical disease (NTD). Its distribution and burden are unknown because of underdiagnosis and underreporting. It is caused by Mycobacterium ulcerans, an environmental pathogen whose environmental niche and transmission routes are not fully understood. The main control strategy is active surveillance to promote early treatment and thus limit morbidity, but these activities are mostly restricted to well-known endemic areas. A better understanding of environmental suitability for the bacterium and disease could inform targeted surveillance, and advance understanding of the ecology and burden of BU. We used previously compiled point-level datasets of BU and M. ulcerans occurrence, evidence for BU occurrence within national and sub-national areas, and a suite of relevant environmental covariates in a distribution modelling framework. We fitted relationships between BU and M. ulcerans occurrence and environmental predictors by applying regression and machine learning based algorithms, combined in an ensemble model to characterise the optimal ecological niche for the disease and bacterium across Africa at a resolution of 5km x 5km. Proximity to waterbodies was the strongest predictor of suitability for BU, followed potential evapotranspiration. The strongest predictors of suitability for M. ulcerans were deforestation and potential evapotranspiration. We identified patchy foci of suitability throughout West and Central Africa, including areas with no previous evidence of the disease. Predicted suitability for M. ulcerans was wider but overlapping with that of BU. The estimated population living in areas predicted suitable for the bacterium and disease was 46.1 million. These maps could be used to inform burden estimations and case searches which would generate a more complete understanding of the spatial distribution of BU in Africa, and may guide control programmes to identify cases beyond the well-known endemic areas.

Understanding the transmission of Mycobacterium ulcerans: A step towards controlling Buruli ulcer

“…Indeed, fine spatial modelling suggests that proximity to waterbodies and related factors were the strongest predictors of Buruli ulcer occurrence and M . ulcerans suitability [ 56 , 57 ]. Likewise, from a social perspective, residents in the Ivory Coast (a Buruli ulcer–endemic region of Africa) also associate unclean water with acquiring Buruli ulcer [ 58 ].…”

Buruli ulcer in Africa: Geographical distribution, ecology, risk factors, diagnosis, and indigenous plant treatment options – A comprehensive review

“…Buruli ulcer (BU) is a necrotizing cutaneous disease caused by Mycobacterium ulcerans, an acid-fast mycobacterium [ [1] , [2] , [3] ]. While the precise mechanism of transmission is not well understood and is likely to be varied, the causative agent appears to spread from aquatic habitats to people via penetrating the skin or indirect transmission mediated by a biting insect vector [ 4 ]. The disease is considered the third most prevalent mycobacterial disease worldwide, after leprosy and tuberculosis [ 5 ].…”

Understanding the Transmission of Bacterial Agents of Sapronotic Diseases in Aquatic Ecosystems: A First Spatially Realistic Metacommunity Model

“…M. ulcerans is now widely distributed in intertropical and subtropical areas. Infections are prevalent in most intertropical regions, but most are concentrated in sub-Saharan Africa where the majority of observed Buruli ulcer cases occur [37]. M. ulcerans charges, also known as parasitic load in disease ecology, in central African continental freshwater ecosystems, vary strongly with seasonal periodicity.…”