Seasonal fluctuations of Simulium damnosum complex and Onchocerca microfilarial evaluation in river systems, South-west Nigeria

Abstract

Seasonal fluctuations of the Simulium damnosum Theobald complex and the prevalence of Onchocerca volvulus Bickel in blackflies caught in river systems bordering the Nigeria -Benin border were assessed for their direct impact on the epidemiology of onchocerciasis in South-western Nigeria. Entomological evaluation and heteroduplex assay (HDA) techniques were performed on flies caught in the eight capture points in the Ogun and Yewa river systems between A total of 5789 blackflies were caught on human bait, of which 727 (12.6%) flies were captured in 2007, 1723 (29.8%) in 2008 and 3339 (57.6%) in 2009. The majority of flies caught during the study were forest flies representing 90.3% of the total catch while savanna flies constituted 9.7%. Proportions of parous to nulliparous flies were low in all the catching points (31.1 and 68.9%, respectively). Of the 5789 flies dissected, 11 (0.2%) flies were infected with Onchocerca parasites with nine of the infected flies having L3 head parasites. The HDA results revealed that the Beffa form of S. soubrense was the dominant cytospecies present (87.1%) in all the capture sites when compared with 12.9% of S. damnosum s.s. The low level of infectivity of flies may therefore indicate a low transmission level of onchocerciasis in the communities along the Ogun and Yewa river systems. However, there is a need for constant surveillance on species composition and fly infectivity in the river systems along the borders of Nigeria -Benin Republic.

Biting behaviour and infectivity of Simulium damnosum complex with Onchocerca parasite in Alabameta, Osun State, Southwestern, Nigeria

“…This could have accounted for the preponderance of forest dwelling flies in the area. However, the results is at variance with earlier results in Osun State, Southwestern Nigeria where the sympatric existence of forest and savannah dwelling flies have been reported [ 15 , 19 , 22 ].…”

Seasonal Variation in Biting Rates of Simulium damnosum sensu lato, Vector of Onchocerca volvulus, in Two Sudanese Foci

“…into savanna flies, which transmit savanna strain of O . volvulus that most often causes blindness, and forest flies, which transmit the forest strain of the parasite that causes skin disease as its main pathogenicity rather than an eye disease [ 6 , 7 ]. The prevalence of human onchocerciasis has been observed to be directly related to the presence and abundance of its vector; therefore, a detailed understanding of parasite and vector population dynamics is crucial for vector control [ 8 ] and is considered as a key component in monitoring the transmission level that measures the success of any of the national and regional control programs [ 9 ].…”

Substrate colonization and relative abundance of immature forms of black flies (Diptera: Simuliidae) in river Mada, Nasarawa State Nigeria

“…S. damnosum sl, the known vector of onchocerciasis was the most dominant specie in each month. The adults of this specie were similarly found to be dominant at Ogun River but with low vectoral capacity [20]. Larvae and pupae belonging to this specie colonized three of the natural substrates viz, trailing leaves, submerged dead leaves and wood.…”