Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Simuliidae”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,153 records · Page 64Linked to original sources
PubMed1994

DNA probe-based classification of Simulium damnosum s. l.-borne and human-derived filarial parasites in the onchocerciasis control program area.

The development of polymerase chain reaction-based methods using strain- and species-specific DNA probes for Onchocerca volvulus has permitted classification of individual parasites from every stage of the parasite's life cycle. This technology has been applied on a large scale basis by Onchocerciasis Control Program (OCP) in West Africa. The primary objective of the OCP in using the DNA probes was to obtain accurate estimates of the annual transmission potential of the blinding strain of O. volvulus. The DNA probe classification of larvae collected throughout the OCP area demonstrated that larvae of less pathogenic strains of O. volvulus and other filarial parasites carried by Simulium damnosum s.l. have resulted in a significant overestimation of the annual transmission potential for blinding onchocerciasis. This effect is particularly pronounced along the southern border of the OCP, where the blinding and less pathogenic strains of O. volvulus coexist, and in the north of the control area, where animal parasites, particularly O. ochengi, may even predominate. A second objective of the OCP in applying the DNA probe technology was to determine the distribution of blinding and less pathogenic O. volvulus in infected individuals along the southern border of the control area. Results obtained from these studies have generally confirmed the distribution pattern established by previous epidemiologic studies. In addition, DNA probe classifications have demonstrated that in areas where the blinding and less pathogenic strains of O. volvulus coexist, a single individual may simultaneously be infected with both strains of the parasite.

Africa, Western↗
PubMed1994

Differential lectin binding of Onchocerca lienalis and Onchocerca ochengi infective larvae following their development in Simulium ornatum s.l.

Lectins have been used to investigate species specific differences in carbohydrate moieties on the surface of the infective larvae of two Onchocerca species following their development in Simulium ornatum. Of the seven FITC-labelled lectins used in this study only two, Arachis hypogea (PNA) and Helix pomatia (HPA), bound to the surface of O. lienalis, whereas no lectin binding could be detected on the surface of O. ochengi infective larvae. This indicates that in principal lectins might be a potential tool for the differentiation of more closely related Onchocerca species.

Animals↗
PubMed1993

Parasitological and clinical characterization of Simulium neavei-transmitted onchocerciasis in western Uganda.

In the forests of western Uganda onchocerciasis is transmitted by Simulium neavei s.s. Since little is known about the infection transmitted by this vector, a survey was made in 1991 with special regard to adult persons of 15 years and older in the 13 villages of the parish Kigoyera 40 km northeast of Fort Portal. 3268 (52%) of the 6271 registered inhabitants were examined clinically and parasitologically. The highest microfilaria (mf) densities were found on the buttocks, lower ones on the shoulders and the lowest on the ankles. In the parish the standardised prevalence of mf carriers was 62%. The crude prevalences of adult mf carriers ranged from 80% to 95% in the 13 villages. Densities of 100 mf/snip or more were found in 25% of male persons. The community microfilarial load (CMFL) in skin snips from the buttocks was 49 mf/snip, ranging from 22 to 93 in the 13 villages. The standardised prevalence of nodule carriers was 25% and the mean nodule load was 1.9 nodules per nodule carrier. Among 3420 nodules 90% were found on the pelvic girdle. The standardised prevalence of onchocercal dermatitis was 19%. The crude rates ranged within the age groups in males from 20% to 45% and in females from 16% to 41%. The standardised prevalence of persons presenting mf in the anterior chamber of the eye was 24% and the CMFL in the anterior chamber ranged between 1.2 and 3.3 mf/chamber in six villages. Standardised rates were 1.6% for sclerosing keratitis and 0.9% for reduced vision of 3/60 or less. These prevalences of eye lesions are comparable to those observed in West African forest areas. The CMFLs and the prevalences of mf and nodule carriers represent suitable criteria for community diagnosis of S. neavei-transmitted onchocerciasis in Uganda to guide ivermectin treatment, whereas the prevalence of "leopard skin" is not useful. Immigrants living less than five years in the endemic focus should be excluded from the assessment of mf carrier rates and those living there less than ten years from rapid assessment of nodule carrier rates.

Adolescent↗
PubMed1993

Distribution of onchocerciasis in selected river basins of four west African countries.

Detailed epidemiological mapping of eight river basins was conducted in four West African countries as part of an effort to identify the communities at risk of onchocercal blindness to guide a programme of large scale ivermectin distribution, attempting control of eye disease. The results show a surprising variability of pattern in the geographical distribution of intensity of onchocerciasis infections in the communities of the river basins investigated. These patterns were at time very different from what was expected on the basis of the available entomological and demographic information. The technique of detailed mapping proved very useful in achieving an excellent coverage of the communities at risk of onchocercal blindness where, so far, satisfactory treatment coverage has been attained for four consecutive yearly treatments.

Animals↗
PubMed1993

Chromosomal diagnostic criteria for some members of Simulium damnosum complex in east Africa.

Identification of Simulium damnosum s.l. vectors of onchocerciasis demands adequate knowledge of the chromosomal features that distinguish human-biting members from nonanthropophilic forms. In this study, 955 S. damnosum larvae collected from various geographical locations in Tanzania were chromosomally analyzed. 358 larvae from small mountain streams in the northeast and central regions of Tanzania, were identified as mainly Nyamagasani and Sanje forms, with only one Kiwira form. 378 larvae from plain and lowland rivers, also in the northeast and central regions, were identified as Nkusi, Kisiwani and Kibwezi forms. Chromosomal examination of 219 larvae from the southern highlands zone revealed the presence of Kiwira and Nyamagasani forms. A further 27 larvae of S. damnosum complex collected from 5 rivers in Uganda were identified as Sebwe and Nkusi forms. Chromosomal photomicrographs on which the distinguishing characters were based are provided. These observations are discussed in the light of previous studies carried out on the S. damnosum cytological forms in Eastern Africa.

Animals↗
PubMed1993

A pictorial guide to the chromosomal identification of members of the Simulium damnosum Theobald complex in west Africa with particular reference to the Onchocerciasis Control Programme Area.

Simulium damnosum Theobald is made up of a complex of sibling species. Nine species are described in the area covered by the World Health Organisation's Onchocerciasis Control Programme in West Africa (OCP). These are, S. squamosum, S. yahense, S. canctipauli, S. soubrense, S. leonense, S. konkourense, S. damnosum s.s., S. sirbanum and S. dieguerense. All of them are vectors of human onchocerciasis, albeit to different capacities. Reliable species determination presently depends on larval cytotaxonomic criteria. The diagnostic chromosomal inversions and other micromorphological characters used in the identification of the species found in the OCP area are presented with figures for their recognition, some distributional information is also given.

Africa, Western↗
PubMed1993

[National entomological teams of the western extension zone of the Onchocerciasis Control Program (OCP) in west Africa from 1986 to 1990].

The western extension area of the Onchocerciasis Control Programme in West Africa (OCP) covers five countries: Guinea, Guinea-Bissau, Mali (western part), Senegal and Sierra Leone. From 1986 to 1990, national teams employed by the respective governments have been regularly collecting entomological data on the vectors of onchocerciasis in these countries. As in the initial programme area of the OCP, the entomological surveillance network was composed of entomological sectors and subsectors (the latter are called "operational bases" in the western extension). In 1990, 308 staff in 47 capture teams were employed for the entomological surveillance activities in seven sectors and twenty-five operational bases. They included a national coordinator as head of the teams for each country, a wide range of technicians, and administrative support staff to assist the national coordinator in the overall management of available resources. The national teams worked under the technical responsibility and supervision of WHO/OCP but with no employee/employer relationship between them and WHO, since they were employed and their salaries were paid by their governments. The OCP, however, paid additional lump sum allowances to each worker, as well as daily subsistence allowances when away from their duty station. Vehicles, entomological equipment, office supplies and furniture, fuel and lubricants were provided by WHO/OCP. Despite the difficulties encountered in the field, which were often great, and their lower salaries (compared with colleagues paid by WHO/OCP), the technical workers in the national teams performed well by OCP standards, with results as satisfactory as those obtained by the WHO/OCP teams in the rest of the programme area. The main reasons for the efficiency and dynamism of the national entomological teams are described. The future of these teams after OCP has ceased its activities is also discussed.

Africa, Western↗
PubMed1993

The population dynamics of Onchocerca volvulus in the human host.

The quantitative aspects of onchocerciasis that focus on the relationship between the number of adult female Onchocerca volvulus in the human host, the total numbers of microfilariae (mfs) in the body at any one time, and the numbers of infective larvae (L3) to which a person is exposed over time, have received little attention. This paper attempts to investigate the problem from three starting points:--(a) using the numbers of palpable nodules to estimate the numbers of productive female worms in the body; (b) using the concentrations of mfs in skin snips to estimate the total load of mfs in the body; and (c) using the Annual Transmission Potential to estimate the numbers of L3 developing to productive female maturity. By analysing published and unpublished data relating to the forest and savanna zones of West Africa, these three approaches indicate that a relatively large proportion of adult female worms lie deep in the body and are impalpable from the surface. They also provide numerical results, of the same order to magnitude, which can be linked to provide estimates of the total numbers of adult female worms and mfs in the bodies of persons with infections of different intensities.

Africa, Western↗
PubMed1993

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 sucrose. The treatment with DMSO + 0.25 M sucrose cryoprotectant resulted in the highest survival of infective larvae. Five cooling rates between 0.5 C/min and 20.0 C/min were applied. The highest survival of L3 was with the cooling rate of 1.0 C/min. Two-step cooling of L3 was applied. In the first step, L3's were frozen to 5 levels from -10.0 C to -20.0 C, -30.0 C, -40.0 C, -60 C, and -80.0 C, and in the second step, larvae were transferred into liquid nitrogen at -196 C for rapid cooling and storage. The survival was the highest when larvae were cooled to approximately -40 C prior to transfer into liquid nitrogen. Slow, gradual, and rapid thawing procedures were applied. The survival was the highest in rapid warming.

Animals↗
PubMed1996

Identification of a common filarial larva in Simulium damnosum s.l. (type D, Duke, 1967) as Onchocerca ramachandrini from the wart hog.

Filarial larvae resembling Type D (Duke, 1967), which are common in the Simulium damnosum s.i. vectors of human onchocerciasis ("riverblindness") in several parts of West Africa, were dissected from wild-caught flies in north Cameroon and examined morphologically. This was done in order to establish a possible synonymy with infective larvae (L3) of 2 recently discovered Onchocerca species of wart hogs (Onchocerca ramachandrini Bain, Wahl, and Renz, 1993 and Onchocerca sp. Wahl and Bain, 1995), which had been found to resemble Type D. After dissection of approximately 1,700 S. damnosum s.1., 13 Type D-like larvae were recovered from 12 infected flies. Their morphology corresponded to O. ramachandrini.

Animals↗
PubMed1995

Technical report. Optimizing probe selection in directed heteroduplex analysis using HDprobe 1.1.

Directed heteroduplex analysis (DHDA) has proven to be a powerful technique for rapid geotyping in human populations. This strategy should also have widespread utility in differentiating closely related organisms of medical and public health importance through identification of DNA sequence polymorphisms. Identifying an optimal probe sequence for use in DHDA has required empirical testing of both the positive and negative strands of a number of potential probes. To identify optimal probes more efficiently, a computer program has been developed that predicts the number of potential stable and unstable mismatches between a probe and its target sequences in DHDA. This information can then be used to predict--from among a group of potential probes--which one will be the most successful in differentiating closely related homologues of a targeted gene sequence. This approach was tested on a number of probe and target sequences derived from the mitochondrial NADH dehydrogenase subunit 4 gene of the West African black fly, Simulium damnosum sensu lato. The number of unstable mismatches predicted to occur in a given heteroduplex by the computer program was found to be important in differentiating closely related species. Therefore, this strategy is useful in identifying informative probes in the development of new DHDA-based assays.

Animals↗
PubMed1995

Cycles in daily catches of members of the Simulium damnosum species complex.

Time series of the numbers of Simulium damnosum s.l. caught biting man each day at various locations in West Africa were investigated using auto-correlation methods and spectral analysis. After differencing the data sets up to the number of times for which significant partial autocorrelations were detected, significant peaks were found in the periodograms of the transformed series in 22 of the 23 series examined. The major peaks revealed the existence of cycles with periodicities of 2 to 3 days, which were interpreted as being indicative of gonotrophic cycle lengths. There was inconclusive evidence suggesting that the cycles for S. squamosum were slightly longer than those for S. damnosum s.str. and or S. sirbanum. One data set with associated parous rates was used to estimate a survival probability per oviposition cycle for S. damnosum/S. sirbanum of 0.46.

Animals↗
PubMed1996

[Microfilarial loads of onchocerca and experimental vectorial capacity of Simulium soubrense-Simulium sanctipauli group in the forest zone of Ivory Coast].

Mass treatment programs using ivermectin are now beginning in forest areas and simuli will soon be feeding on individuals with low microfilarial loads (probably < 10). Most previous reports have involved higher mean loads (range: 14-6950. The purpose of this study was to ascertain the impact of low microfilarial loads on the number of infecting larvae present at the end of a parasite cycle in the Simulium soubrense-Simulium sanctipauli group and on availability for transmission to man by inoculation. Tests were carried out on five subjects from a forest area of southwest Ivory Coast who were infected with onchocerciasis and presented mean microfilarial loads of 1, 5, 10, 20, and 100. Findings showed a direct correlation between microfilarial load (1, 5, 20, and 100) and intake of microfilaria per dissected female. Similarly there was a correlation between microfilarial loads (1, 5, 10, 20, and 100), quantity of infected females, and number of infecting larvae per infected female. Parasite output was variable but decreased as microfilarial load increased. This study suggests that the experimental vectorial capacity of simuli is similar in subjects presenting onchocerciasis with high and low microfilarial loads.

Animals↗
PubMed1997

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 cylindroid lumen becomes partially occluded with microvilli formed by the evaginations of the apical membranes of the intestinal epithelium. Cross sections, through this region reveal that groups of 5 radiating epithelial cells are joined near the lumen surface by junctional complexes. The alimentary canal terminates via a rectal valve and channel supported by somatic and neural cells. The central nervous system consists of a nerve ring that surrounds the muscular region of the esophagus. Related neurons support chemoreceptors and tactoreceptors of sensilla and the extensive coelomyarian and meromyarian somatic muscles. Extensive accumulations of glycogen rosettes are present in many of the muscle and hypodermal cells.

Animals↗
PubMed1997

The relevance of neural architecture to visual performance: phylogenetic conservation and variation in Dipteran visual systems.

In cyclorrhaphan flies, giant tangential neurons in the lobula plate are supplied by isomorphic arrays of evolutionarily conserved achromatic elementary motion detecting circuits originating in the retina. The arrangements among giant tangential neurons is characteristic of a taxon and can differ between taxa having different visual performances. Observations of 12 brachyceran and 4 nematoceran species have identified different behaviors associated with visually stabilized flight. Neuroanatomical comparisons between closely related species having different behaviors and phylogenetically distant species that have similar behaviors suggest that such differences relate to differences of giant tangential cell architecture in the lobula plate. These functionally related differences contrast to anatomical features that reflect phylogenetic affinities. For example, the lobula plates of robber flies, typified by ballistic flight behavior, all differ from other taxa in lacking cyclorrhaphan-type vertical motion-sensitive neurons; instead, they possess an extra complement of horizontal cells in their place. The results suggest that, although circuits that compute elementary motion are conserved across the Diptera, selective pressure has resulted in modifications of their target neurons, thus contributing to the wide variety of visual behaviors observed within this group of insects.

Animals↗
PubMed1997

Required duration of combined annual ivermectin treatment and vector control in the Onchocerciasis Control Programme in west Africa.

In the extension areas of the Onchocerciasis Control Programme in West Africa, aerial larviciding is supplemented with annual ivermectin treatment, mainly to achieve better control of morbidity. The purpose of this study is to determine whether and to what extent the addition of annual ivermectin treatment permits earlier cessation of vector control than originally recommended. The effectiveness of combined ivermectin distribution and vector control was assessed using an epidemiological model. Model predictions suggest that, dependent on the pre-control endemicity of the area and the proportion of persons treated during each ivermectin round, large-scale annual treatment permits a considerable reduction in the duration of vector control. Taking into account uncertainty about the efficacy of ivermectin, our results indicate that, provided treatment coverage is at least 65% and there is no importation of infection from elsewhere, 12 years of combined control will be sufficient to reduce the risk of recrudescence to below 1% in even the most afflicted areas.

Adolescent↗
PubMed1997

Reduced prevalence of onchocerciasis in Uganda following either deforestation or vector control with DDT.

To determine the prevalence of onchocerciasis in western Uganda following deforestation and vector control, three foci were re-examined 20 years after previous surveys. In the Ruteete focus Simulium neavei had apparently disappeared and the prevalence of onchocerciasis declined in adults from about 70% in 1971 to a standardised prevalence of 12% in 1992. An increase of population density together with extended deforestation was assumed as cause of this strong reduction. In Bugoye, a S. damnosum s.l. focus, the standardised prevalence of microfilaria carriers declined from 62% in 1972 to 4.7% in 1992. Entomological data indicated the absence of man biting blackflies in the nineties. It can be suggested that the vector control using DDT performed during the seventies had lead to a change of the species composition from anthropophilic to non-anthropophilic S. damnosum s.l. In the focus Kicheche environmental changes were insignificant, deforestation was not progressive and S. neavei was abundant. Here the standardised prevalence of microfilaria carriers was still high (61%).

Adolescent↗