Authors: Adeleke, M. A, Sam-Wobo, S. O, Olatunde, G. O, Akinwale, O. P, Ekpo, U. F, Mafiana, C. F.
Journal of Rural and Tropical Public Health 2011 Vol. 10 pp. 39-43
Abstract
Objectives: A longitudinal study was carried out to investigate the adult population dynamics and the physical and chemical factors affecting the distribution of Simulium damnosum complex, a vector of
onchocerciasis (river blindness) along the Osun river in a forest zone of southwestern Nigeria. Methods: Adult flies were collected on consenting human baits from 7.00 am to 6.00 pm every fortnight at three communities (Osun Eleja, Osun Ogbere and Osun Budepo) along the Osun River from February 2008 to June 2009. Larva were looked for in all accessible rivers around the study area and their physical-chemical parameters were determined. Results: A total of 1472 flies were caught during the study period with Osun Budepo accounting for the highest number of the flies (47.0%) followed by Osun Eleja (42.2%) and Osun Ogbere (10.8%). The fly abundance was significantly higher (p<0.05, respectively for the three sites) during the wet season, with a positive correlation between rainfall and fly abundance at the three sites. S. damnosum s.l was found breeding only in the wet season in the rivers with rocky substratum and submerged vegetations. Water velocity (p=0.050) and dissolved oxygen (p=0.042) were the only parameters showing significant associations with the distribution of S. damnosum s.l larvae at the breeding sites. The adults of S. damnosum s.l were found biting near rivers hitherto scored negative for preimaginal stages, showing that the presence of larvae is not the sole factor in determining the extent of the distribution of the S. damnosum complex. Conclusions: The results suggest that the climatic and environmental conditions influence the distribution of S. damnosum s.l in the study area. The presence of the fly all year round calls for adequate control measures to curtail the transmission of onchocerciasis, in particular during the wet season.
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