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

Kelly-Hope, Louise ORCID:, Unnasch, Thomas R, Stanton, Michelle ORCID: and Molyneux, David ORCID: (2015) 'Hypo-endemic onchocerciasis hotspots: defining areas of high risk through micro-mapping and environmental delineation.'. Infectious diseases of poverty, Vol 4, Issue 36.

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Onchocerciasis (river blindness) caused by the parasite Onchocercavolvulus and transmitted by riverine 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 Loa loa, a filarial parasite widespread in Central and West Africa, which causes Tropical eye worm and transmitted by Chrysops spp. (Deer flies).


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 L. loa co-endemic areas. First, we demonstrate that micro-stratification overlap mapping (MOM) of available onchocerciasis and loiasis prevalence maps can be used to identify 12 key high risk areas, where low O. volvulusand high L. loa transmission overlap, which we define as "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 Simulium spp. and Chrysops spp. vector habitats can further help to define target intervention areas i.e. secondary hotspots within hotspots, to help avoid the risk of SAEs.


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 L. loa associated risks, especially if there are extensive areas of low endemicity that may require treatment with ivermectin or alternative strategies. Novel cost-effective approaches are necessary if elimination of O.volvulus transmission in Africa is to be achieved in an efficient and safe way by the goal of 2025.

Item Type: Article
Uncontrolled Keywords: Onchocerciasis, River blindness, Loa loa, Loiasis, Severe adverse events, Mapping, Elimination, Environment, Africa
Subjects: QX Parasitology > Helminths. Annelida > QX 301 Filarioidea
WB Practice of Medicine > Medical Climatology > WB 710 Diseases of geographic areas
WC Communicable Diseases > Tropical and Parasitic Diseases > WC 885 Onchocerciasis
Faculty: Department: Biological Sciences > Department of Tropical Disease Biology
Digital Object Identifer (DOI):
Depositing User: Mary Creegan
Date Deposited: 09 Dec 2015 12:33
Last Modified: 06 Sep 2019 10:55


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