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Parasit Vectors. 2016 Oct 10;9(1):536.

Discrimination between Onchocerca volvulus and O. ochengi filarial larvae in Simulium damnosum (s.l.) and their distribution throughout central Ghana using a versatile high-resolution speciation assay.

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Department of Animal, Plant and Soil Sciences, La Trobe University, Bundoora, 3086, Australia.
current address: Wellcome Trust Sanger Institute, Wellcome Genome Campus, Hinxton, Cambridgeshire, CB10 1SA, UK.
Department of Animal, Plant and Soil Sciences, La Trobe University, Bundoora, 3086, Australia.
Council for Scientific and industrial Research, Water Research Institute, Accra, Ghana.
Department of Comparative Zoology, Institute of Evolution and Ecology, University of Tübingen, Auf der Morgenstelle 28, 74074, Tübingen, Germany.
Department of Parasitology, Liverpool School of Tropical Medicine, Liverpool, UK.



Genetic surveillance of the human filarial parasite, Onchocerca volvulus, from onchocerciasis endemic regions will ideally focus on genotyping individual infective larval stages collected from their intermediate host, Simuliid blackflies. However, blackflies also transmit other Onchocerca species, including the cattle parasite O. ochengi, which are difficult to distinguish from the human parasite based on morphological characteristics alone. This study describes a versatile approach to discriminate between O. volvulus and O. ochengi that is demonstrated using parasite infective larvae dissected from blackflies.


A speciation assay was designed based on genetic differentiation between O. volvulus and O. ochengi mitochondrial genome sequences that can be performed in high-throughput high-resolution melt (HRM)- or lower throughput conventional restriction fragment length polymorphism (RFLP) analyses. This assay was validated on 185 Onchocerca larvae dissected from blackflies captured from 14 communities in Ghana throughout 2011-2013. The frequency of O. ochengi was approximately 67 % of all larvae analysed, which is significantly higher than previously reported in this region. Furthermore, the species distribution was not uniform throughout the study region, with 25 %, 47 % and 93 % of O. volvulus being found in the western-most (Black Volta, Tain and Tombe), the central (Pru) and eastern-most (Daka) river basins, respectively.


This tool provides a simple and cost-effective approach to determine the identity and distribution of two Onchocerca species, and will be valuable for future genetic studies that focus on parasites collected from blackflies. The results presented highlight the need to discriminate Onchocerca species in transmission studies, as the frequency of each species varied significantly between the communities studied.


Ghana; High-resolution melt analysis (HRM); Onchocerca ochengi; Onchocerca volvulus; Onchocerciasis; Restriction fragment length polymorphism (RFLP); Speciation

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