| the transmission of onchocerciasis at a forest village in sierra leone. i. simulium damnosum s.l. biting densities and infection with onchocerca volvulus at five representative sites. | previous studies in the forest area of sierra leone have shown that transmission of onchocerca volvulus takes place many kilometers away from large breeding rivers and sometimes in open farmland. to determine where and when people in a forest village were most likely to be infected, catches of simulium damnosum s.l. were carried out every week for 12 months, at five sites in and near a village where onchocerciasis was mesoendemic. the number of flies caught per man a day at open farm sites was s ... | 1990 | 2076037 |
| effect of mass treatment of a human population with ivermectin on transmission of onchocerca volvulus by simulium yahense in liberia, west africa. | the impact of mass treatment with ivermectin on the intensity of onchocerca volvulus transmission by the black fly (simulium yahense) was evaluated on the liberian agricultural company rubber plantation in liberia, west africa. the adult pre-treatment prevalence of onchocerciasis was greater than 80%, and the average intensity of infection was 5.35 mf/mg of skin. the drug was administered at 2 annual intervals, reaching 58-60% of the approximately 14,000 people living in 73 camps. landing/biting ... | 1990 | 2316786 |
| ocular onchocerciasis and intensity of infection in the community. ii. west african rainforest foci of the vector simulium yahense. | a novel method of analysis was used to describe community patterns of ocular onchocerciasis in relation to the intensity of infection in west african forest villages where s. yahense is the sole vector. the pattern is completely different from that found in the savanna, even after correction for the intensity of infection as measured by the community microfilarial load (cmfl). lesions of the anterior segment of the eye as well as onchocercal blindness either do not occur or occur only sporadical ... | 1989 | 2559472 |
| identification of larval and adult simulium yahense and simulium sanctipauli based on species-specific enzyme markers and their distribution at different breeding habitats in central liberia. | human-biting adults and late instar larvae of the simulium damnosum complex from four ecologically different simuliid breeding habitats in the firestone rubber plantation at harbel, liberia, were identified morphologically and the monthly species composition of each site was recorded. samples of the predominant species found at each site were assayed electrophoretically for species-specific variants of phosphoglucomutase (pgm) and trehalase (tre). enzyme identifications of flies and larvae were ... | 1986 | 2947482 |
| population relationships of simulium yahense and simulium sanctipauli in the firestone rubber plantation at harbel, liberia. | comparative genetic differences for the phosphoglucomutase and trehalase loci were surveyed in larval and adult blackfly populations of the onchocerciasis vectors simulium yahense vajime and dunbar, and s.sanctipauli vajime and dunbar. genotype frequencies for each stage and all populations were at hardy-weinberg equilibrium, indicating that s.yahense and s.sanctipauli remain genetically distinct. s.yahense populations from three different locations were found to be genotypically comparable. the ... | 1988 | 2980977 |
| large scale production of the vertebrate infective stage (l3) of onchocerca volvulus (filarioidea: onchocercidae). | laboratory-derived simulium yahense and s. sanctipauli females were used to produce large numbers of onchocerca volvulus infective stage larvae (l3) for use in assessing the possible chemoprophylactic potential of ivermectin in the chimpanzee model. engorgement rates and subsequent post-prandial survival were correlated with the time at which adult flies were offered a carbohydrate source following emergence and the age of flies that fed on microfiladermic volunteers. | 1988 | 3275138 |
| quantitative studies of onchocerciasis transmission by simulium yahense and simulium sanctipauli in the firestone rubber plantation at harbel, liberia. | black fly vectors of onchocerciasis from three ecologically different simuliid breeding habitats in the firestone rubber plantation at harbel, liberia, were surveyed by human-biting collections conducted at weekly intervals over a 13-month period. black flies were identified morphologically and the monthly and seasonal contribution of different vector species to the transmission of onchocerca volvulus at each site was determined. simulium yahense was identified as the predominant vector species ... | 1987 | 3578652 |
| failure of onchocerca gutturosa to develop in simulium soubrense and simulium yahense from liberia. | laboratory reared female s. soubrense and s. yahense from liberia were intrathoracically inoculated with bovine skin dwelling microfilariae of onchocerca gutturosa. of a total of 174 flies, each injected with 50 fresh microfilariae, the maximum development was to late first-stage larvae. one s. soubrense also contained two second-stage larvae and a maldeveloped third-stage larvae. no development to normal third-stage larvae was observed in any fly despite maintenance at 28 degrees c for up to 10 ... | 1987 | 3629136 |
| the engorgement ratio of simulium yahense (diptera: simuliidae) at the firestone rubber plantation, harbel, liberia. | | 1986 | 3735334 |
| the effects of ivermectin on transmission of onchocerca volvulus. | ivermectin, given to onchocerciasis patients as a single oral dose of 200 micrograms per kilogram of body weight, substantially reduced the uptake of onchocerca volvulus microfilariae by simulium yahense, an efficient black fly vector of the parasite in the tropical rain forests of west africa. three months after treatment, patients given ivermectin infected flies at a significantly lower rate than those who had received diethylcarbamazine or placebo, thereby reducing the number of developing la ... | 1986 | 3753801 |
| histochemical enzyme variation in onchocerca volvulus microfilariae from rain-forest and sudan-savanna areas of the onchocerciasis control programme in west africa. | histochemical staining methods for acid phosphatase were used to study the differences among microfilariae of various west african strains of onchocerca volvulus in both forest and sudan-savanna onchocerciasis zones. the results have shown statistically significant differences in the staining patterns of microfilarial populations in the two zones. in the rain-forest areas, where onchocerciasis is transmitted by simulium yahense, s. sanctipauli, s. soubrense and s. squamosum, there were no signif ... | 1982 | 6186410 |
| transmission of onchocerciasis by local black flies on the firestone rubber plantation, harbel, liberia. | a quantitative description of the transmission dynamics of onchocerciasis on the firestone rubber plantation, harbel, liberia is presented. the putative vector, simulium yahense, comprised 98.5% of the flies examined. diurnal vector-host contact was unimodal, expressing a distinct peak between 0800 and 1100 hours, particularly during the wet season. perennial breeding occurs in the firestone biotope, and is manifested by a mean annual daily landing rate of 75 flies per person per day. s. yahense ... | 1984 | 6476202 |
| [onchocerciasis control program in west africa: socioeconomic development and risk of recrudescence of transmission. 2. experimental study of the transmission of onchocerca volvulus strains from southwestern sierra leone by simulium yahense and simulium squamosum]. | the movements of human populations towards the mining wealth of the northern parts of sierra leone are favorable to a high contact rate between onchocerciasis patients coming from the south-western area of this country and the vector species simulium yahense and simulium squamosum which assume the essential of onchocerciasis transmission in the above-mentioned mining area. in fact, the onchocerca volvulus strains concerned by this contact seem to be more pathogenic than those locally transmitted ... | 1994 | 7944649 |
| diurnal biting activity and transmission of onchocerca volvulus (filariata: onchocercidae) by simulium yahense (diptera: simuliidae) in liberia. | to determine the influence of meterological factors on the diurnal biting cycle of simulium yahense vajime & dunbar (a member of the simulium damnosum theoblad complex), we captured host-seeking females as they landed on the exposed lower legs of humans in the harbel area of liberia. biting activity was greatest during the morning hours and was characterized by a unimodal harmonic curve. although meteorological conditions had no decisive influence on the unimodal pattern of diurnal biting activi ... | 1994 | 8189413 |
| cryopreservation of infective larvae of onchocerca volvulus (filarioidea: onchocercidae). | infective larvae (l3) of onchocerca volvulus were procured in liberia, west africa, in the natural black fly vector, simulium yahense. a cryobiological technique was developed to preserve l3 of o. volvulus that were fully viable after thawing. larvae were treated before cooling with 4 cryoprotective compounds. three compounds, dimethyl sulfoxide (dmso), glycerol, and ethylene glycol, were prepared with distilled water. the fourth compound was dmso prepared in different concentrations with 0.25 m ... | 1993 | 8410541 |
| ultrastructure of infective larvae (l3) of onchocerca volvulus (nematoda: filarioidea) developed in simulium yahense in liberia. | third-stage infective larvae of onchocerca volvulus were examined to elucidate the ultrastructure and the interrelations of the stoma, esophagus, intestine, and nervous system. the alimentary canal involves a cuticularized stoma with a triradiate lumen that is continuous with a similar triradiate lumen in the muscular region of the esophagus. the lumen wall may be laterally appressed or opened into a stellate form in the glandular region. posteriad from the esophagointestinal valve, the cylindro ... | 1997 | 9194812 |
| similar blackfly attraction by onchocerciasis patients and individuals putatively immune to onchocerca volvulus. | in areas endemic for onchocerciasis, a small number of individuals show no detectable infection with onchocerca volvulus despite an apparently similar exposure to the transmitting blackflies. such individuals have been termed putatively immune. since several studies have indicated marked host differences in attractiveness for blood-seeking insects, putative immunity in o. volvulus infection may result, at least in part, from low vector attractiveness of the respective individuals. in an area hyp ... | 1999 | 10674077 |
| development of onchocerca volvulus (filarioidea: onchocercidae) in the west african black fly simulium yahense (diptera: simuliidae) in liberia. | simulium yahense black flies infected with microfilaria of onchocerca volvulus were kept in a defined insectary environment in liberia, west africa. a daily sample of infected flies was dissected for larvae developing in the thoracic muscles and examined for growth in stadial development. microfilariae ingested by black flies transformed to the l1 larval stage without molting. successive larval development included molting to the l2 stage and, finally, to the l3 stage, which was infective in hum ... | 2001 | 11780809 |
| the cytotaxonomy and morphotaxonomy of simulium mengense (diptera: simuliidae). | human onchocerciasis is hyper-endemic in south-western cameroon and the island of bioko. the vector on the island is the endemic 'bioko' form of simulium yahense. on the mainland, s. damnosum s.s., s. squamosum and s. mengense are recorded around mount cameroon but their contribution to transmission in the area is unclear. as elimination of onchocerciasis, through vector eradication, is a possibility on the island, it is important to be able to identify vector flies which might migrate to bioko ... | 2004 | 15257801 |
| consequences of vector behavior in epidemiology of onchocerciasis on the firestone rubber plantation in liberia. | in the current study, we have assessed the distribution of black fly vectors and the occurrence of onchocerciasis among residents of the firestone rubber plantation (frp) in liberia. the degree of endemicity of onchocerciasis on the frp is correlated with the breeding of simulium yahense on the du river and simulium soubrense on the farmington river, as well as with the feeding behavior of these black fly vectors. s. yahense is highly anthropophilic and highly susceptible to onchocerca volvulus, ... | 2006 | 16687689 |
| the elimination of the onchocerciasis vector from the island of bioko as a result of larviciding by the who african programme for onchocerciasis control. | the island of bioko is part of the republic of equatorial guinea and is the only island in the world to have endemic onchocerciasis. the disease is hyperendemic and shows a forest-type epidemiology with low levels of blindness and high levels of skin disease, and the whole population of 68,000 is estimated to be at risk. control of onchocerciasis began in 1990 using ivermectin and this yielded significant clinical benefits but transmission was not interrupted. feasibility and preparatory studies ... | 2009 | 19619686 |
| assessments of the transmission of onchocerca volvulus by simulium sanctipauli in the upper denkyira district, ghana, and the intermittent disappearance of the vector. | following studies on the transmission of onchocerca volvulus (leuckart) by simulium sanctipauli vajime & dunbar (diptera, simuliidae) in upper denkyira district in ghana in 2001 and 2002 (kutin et al., med vet ent 18:167-173, 2004), further assessments were carried out in 2006 and 2013/2014 to determine whether transmission parameters had changed since community-directed ivermectin treatment (cdti) began in 1999. there were no marked changes of the transmission intensities in 2006. only slight, ... | 2015 | 25592754 |
| cytotaxonomy, morphology and molecular systematics of the bioko form of simulium yahense (diptera: simuliidae). | cytotaxonomic analysis of the polytene chromosomes from larvae of the simulium damnosum theobald complex from the island of bioko in equatorial guinea is reported, and a new endemic cytoform is described. chromosomally this cytoform is close to both s. squamosum (enderlein) and s. yahense vajime & dunbar, but is not identical to either. however, it is morphologically and enzymatically identical to s. yahense. the bioko form was also found to differ from other cytoforms of the s. damnosum complex ... | 2003 | 12699536 |
| assessment of rdna igs as a molecular marker in the simulium damnosum complex. | for five cytospecies of the simulium damnosum theobald complex of blackflies (diptera: simuliidae) from west africa, both ends of the intergenic spacer region (igs) of the rdna have been sequenced with the aim of developing specific molecular markers. no specific differences in these two regions were detected between simulium sanctipauli v. & d., simulium sirbanum v. & d., simulium soubrense v. & d., simulium squamosum enderlein and simulium yahense v. & d., except in the number of a subrepeats ... | 2002 | 12510892 |
| sibling species distributions of the simulium damnosum complex in the west african onchocerciasis control programme area during the decade 1984-93, following intensive larviciding since 1974. | during the decade from 1984 to 1993, nine species of the simulium damnosum complex of blackflies (diptera: simuliidae) were identified from the area covered by the onchocerciasis control programme. these were s. damnosum s.s., s. dieguerense, s. konkourense, s. leonense, s. sanctipauli, s. sirbanum, s. soubrense, s. squamosum, and s. yahense. some of these species were found to consist of two chromosomal variant populations. these were s. konkourense 'konkouré' and 'menankaya' forms, s. sanctipa ... | 1998 | 9824818 |
| distribution of simulium yahense after larviciding activities in the southern extension of the onchocerciasis control programme. | the distribution range of simulium yahense in the eastern operational area of the onchocerciasis control programme increased after larviciding treatments were started in 1988, to control important simulium damnosum s. 1. vectors of onchocerciasis. a distribution map indicating the extended range is drawn and the importance of this expansion of s. yahense to disease transmission discussed. | 1992 | 1598516 |
| natural interspecific hybridisation of simulium sanctipauli s.l. with simulium squamosum and simulium yahense (diptera: simuliidae). | natural hybridisation between simulium sanctipauli (sensu quillevéré et al. 1981) and simulium squamosum/yahense occurs at a rate of around 0.001. a single larva has been found which is unambiguously a backcross between s. sanctipauli s.l. and a s. sanctipauli s.l. x squamosum/yahense hybrid. this discovery indicates the possibility of genetic introgression between these species. examination of the polytene chromosomes of this backcross progeny and subsequent re-examination of the type specimens ... | 1984 | 6710602 |
| the vectorial efficiency of simulium yahense populations in south-eastern ghana. | adult female simulium yahense were identified amongst catches of s. damnosum s. 1. caught at tsatsadu falls and wegbe in south-eastern ghana. dissections of stained flies to assess the species' role as a vector of onchocerciasis in the region revealed as many as 357 l3 per 1000 biting flies in a sample from wegbe. when the data from the two sites were combined 154 l3 per 1000 biting flies and 315 l3 per 1000 parous flies were recorded. the values for wet season samples were about 12% higher than ... | 1992 | 1598512 |
| duration of larval development of simulium yahense (diptera: simuliidae) under natural conditions. | the duration of simulium yahense vajime & dunbar larval development on a dam spillway in harbel, liberia, was observed to make accurate decisions regarding the frequency of larvicide treatments against this onchocerciasis vector. larval development required a minimum of 10-12 d from eclosion to first pupation. initial larvicidal treatment for s. yahense control would require a treatment cycle of 7 d. once suppression of adult and larval populations is achieved, a 9-12-9-12 day treatment cycle co ... | 1992 | 1552515 |
| morphological identification of simulium yahense and s. squamosum in the south of sierra leone confirmed by enzyme electrophoresis. | | 1988 | 3256123 |