A cross-sectional study of Simulium damnosum s.l. breeding sites and species distribution in sudan savanna, mixed savanna-forest and rainforest regions in Cameroon

Abstract

Background: The presence of breeding sites and distribution of species of Simulium damnosum s.l are critical in understanding the epidemiology of onchocerciasis and evaluating the impact of elimination interventions. Reports on breeding sites and species distribution of members of S. damnosum s.l in Cameroon are scarce and the few available date back to more than 3 decades. The aim of this study is to provide information on S. damnosum breeding sites across the rainy (RS) and dry (DS) seasons and the species composition in three different regions in Cameroon: Southwest (SW), Northwest (NW) and North (N).Methods: A cross-sectional two-seasons study was carried out in three regions with different ecological characteristics (SW – rainforest; NW- mixed forest-Guinea savanna; N- Sudan savanna). Pre-control onchocerciasis endemicity, relief maps and historical entomological information were used to identify potential rivers for purposive sampling. Sampled larvae were fixed in Carnoy’s solution, sorted and S. damnosum s.l larvae stored until identification by cytotaxonomy. Geographical coordinates of potential breeding sites were recorded to produce maps using ArcGIS, while SPSS used for Chi-square test to estimate difference between blackfly seasonal breeding rates.Results: 237 potential breeding sites were sampled (RS=81; DS=156) and 72 were found positive for S. damnosum s.l. SW had the most positive sites [67 (RS=24; DS=43)], having significant difference in rate of breeding between the seasons (p<0.05). Among 68 sites visited in both seasons, 16(23.5%) were positive in one of two seasons, 14(20.6%) and 38(55.9%) respectively positive and negative in both seasons, and more sites positive in DS(11) than in RS(05). Simulium damnosum s.s and S. sirbanum were the main species in N while S. squamosum and S. mengense the predominant species in NW and SW. S. soubrense and S. yahense were uniquely recorded in SW.Conclusions: A comprehensive mapping of breeding sites requires rainy and dry seasons sampling. Study also demonstrates S. damnosum s.l breeding site survey is achievable in forest as in savanna zones. Not all potential breeding sites are actual breeding sites. Observation of S. soubrense in SW indicates changes in species composition over time and could affect onchocerciasis epidemiology in this area.