Hypo-endemic onchocerciasis hotspots: defining areas of high risk through micro-mapping and environmental delineation.

Background: Onchocerciasis (river blindness) caused by the parasite and transmitted by riverine Onchocercavolvulus Simulium spp. (Black flies) is targeted for elimination in Africa. This is a significant change in strategy from the 'control' of meso- and hyper-endemic areas through mass drug administration (MDA) with Mectizan® (ivermectin), to the 'elimination' in all endemic areas where a range of interventions may be required. The most significant challenges of elimination in low transmission or hypo-endemic areas are two-fold. First, there are vast remote areas where the focality of low transmission is relatively undefined. Second, the treatment with ivermectin increases the risk of serious adverse events (SAEs) in individuals with high parasitaemias of, a filarial parasite widespread Loa loa in Central and West Africa, which causes Tropical eye worm and transmitted by spp. (Deer flies). Chrysops Discussion: We therefore propose novel mapping approaches using remote sensing satellite and modelled environmental data to be used in combination with rapid field surveys to help resolve the problems of targeting the expansion of onchocerciasis elimination activities in co-endemic areas. First, we demonstrate that L. loa micro-stratification overlap mapping (MOM) of available onchocerciasis and loiasis prevalence maps can be used to identify 12 key high risk areas, where low and high transmission overlap, which we define as O. volvulus L. loa "hypo-endemic hotspots". Second we show that integrated micro-mapping of prevalence data, and the use of environmental data to delineate riverine and forest risk factors associated with spp. and spp. Simulium Chrysops vector habitats can further help to define target intervention areas i.e. secondary hotspots within hotspots, to help avoid the risk of SAEs. Summary: These mapping examples demonstrate the value of bringing prevalence, entomological and ecological information together to develop maps for planned implementation and targeted strategies. This is critical as better mapping may the reduce costs and lower the associated risks, especially if there are L. loa extensive areas of low endemicity that may require treatment with ivermectin or alternative strategies. Novel cost-effective approaches are necessary if elimination of transmission in Africa is to be achieved in an O.volvulus efficient and safe way by the goal of 2025. [ABSTRACT FROM AUTHOR]