Multidimensional complexities of filariasis control in an era of large-scale mass drug administration programmes: a can of worms

Abstract

The impact of control and elimination programmes by mass drug administration (MDA) targeting onchocerciasis and lymphatic filariasis (LF) in sub-Saharan Africa over the last two decades has resulted in significantly reduced prevalence and intensity of infection, with some areas interrupting transmission. However, given that these infections are often co-endemic and the drugs (either ivermectin alone or combined with albendazole) also impact on soil transmitted helminths (STH), the importance of this, in terms of reaching the global goals has not been assessed. The additional problem posed by Loa loa, where ivermectin cannot be safely administered due to the risk of serious adverse events compounds this situation and has left populations drug naïve and an alternative strategy to eliminate LF is yet to be initiated at scale. Here, we present a series of operational research questions, which must be addressed if the effectiveness of integrated control of filarial and helminth infections is to be understood for the endgame. This is particularly important in the diverse and dynamic epidemiological landscape, which has emerged as a result of the long-term large-scale mass drug administration (or not). There is a need for a more holistic approach to address these questions. Different programmes should examine this increased complexity, given that MDA has multiple impacts, drugs are given over different periods, and programmes have different individual targets.

Figures

Figure 1

Cross-cutting treatments and intervention for helminthiases (filarial and soil–transmitted) and malaria. For STH moderate endemic areas (prevalence >20%) once yearly albendazole treatment is given, and in high endemic areas (prevalence >50%) twice yearly albendazole treatment is given. For LF/L loa co-endemic areas twice yearly albendazole treatment is given together with bed nets/LLINs.

Figure 2

Loiasis intermediate and high risk subnational areas. Risk coding based on loiasis map by Zouré et al.[47] and created using country sub-national boundaries in ArcGIS (ESRI, Redlands, CA).

Figure 3

Maps of loiasis intermediate and high risk areas geographically overlapping with CDTi and non-CDTi areas. Orange shading indicates loiasis intermediate prevalence areas of 20-40%. Red shading indicates loiasis high prevalence areas of > 40%. Blue shading indicates onchocerciasis > 20% and areas targeted with ivermectin, also known as CDTi areas. A. Loiasis >20% B. Onchocerciasis >20% (CDTi areas) C. Loiasis and CDTi area overlap D. Loiasis overlapping CDTi areas E. Loiasis overlapping non-CDTi areas.