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 775 records · Page 43Linked to original sources
PubMed1983

Identification of a laboratory mating form of the Simulium damnosum Theobald complex in West Africa.

Larvae and pupae of Simulium damnosum s.l. were collected from the Begba rapids on the Mono river. Emerging adults were induced to mate, blood feed and oviposit. Six out of 13 discrete egg batches counted were fertile. The F1 females did not blood feed and thus no F2 eggs were obtained. Larvae from the breeding site and the F1 generation were identified as being the Beffa form of the S. sanctipauli/S. soubrense group. This form appears to be the only member of the S. damnosum complex in West Africa which mates in the laboratory and is almost certainly the same form as that colonized by Simmons and Edman (1982). The mating behaviour of West African S. damnosum s.l. described by several authors is similar to that observed in the Beffa form, and the possibility that earlier reports referred to the Beffa form is discussed.

Africa, Western↗
PubMed1983

Variation and distribution of forms of Simulium soubrense and S. sanctipauli in West Africa.

Examination of specimens from savanna areas of Togo and Benin attributable to Simulium soubrense and S. sanctipauli according to the criteria of Vajime and Dunbar (1975) revealed hitherto undescribed features. Cytological examination showed many larvae with the arrangement IIL- 4.6/4.6.7, heterozygous for the 'diagnostic' inversion and 86% of the males possessed a previously undescribed inversion IIS-6b. The occurrence of such larvae in Togo and Benin was associated in adult males with records of a type of scutal pattern which is described and termed Type IV. This pattern is one extreme of a range of scutal pattern variation in the males of the S. soubrense/S. sanctipauli sub-group, which was separated into four arbitrary classes and specimens were scored as Type I, II, III or IV. The distribution of these different types of male scutal pattern, based on collections made in West Africa between 1963 and 1981, is presented. Type I and II patterns predominated in forest areas and Type IV in savanna. Many female flies which occurred together with the latter possessed pale wing tufts. In the light of the above and additional evidence, derived from the progeny of individual females, and because the 'diagnostic' inversion for S. soubrense and S. sanctipauli together with a previously undescribed sequence IIL-6 occurred in Hardy-Weinberg equilibrium, it was concluded that the populations in Togo and Benin are a single interbreeding group. This group is described as a new form, named the Beffa form, of the S. soubrense/S. sanctipauli subgroup of the S. damnosum s.l. complex and its possible taxonomic status is discussed.

Africa, Western↗
PubMed1984

Peritrophic membrane formation in three temperate simuliids, Simulium ornatum, S. equinum and S. lineatum, with respect to the migration of onchocercal microfilariae.

Engorged females of three temperate simuliid species, Simulium ornatum, S. lineatum and S. equinum, were collected immediately after their bloodfeeds from a cow host. Midguts were dissected out at selected time intervals thereafter, from two minutes to 24 hours post engorgement (p.e.) and peritrophic membrane formation observed. There was an initial rapid secretion of peritrophic membrane (PM) material from the midgut epithelium. The peritrophic membrane produced is Type 1, being formed by delamination from the entire midgut epithelium. This secretory phase continued for approximately two hours p.e. in all three species and was followed by a period of organization within the membrane. At between 12 and 24 hours p.e., the PM appeared more organized and was associated with the formation of several distinct laminae in both S. ornatum and S. lineatum, although in S. equinum it consisted of only a single homogenous layer. Both the rate of secretion and the resulting morphological appearance of the PM appeared species-specific and there was great variation in its thickness in all three species at all time intervals examined. It is suggested that microfilariae penetrate the PM during the initial period of its secretion before it has condensed to form a distinct structure. Furthermore, the migration of microfilariae may be restricted to, or enhanced by, the presence of very thin areas within the membrane where erythrocytes lie almost adjacent to the midgut epithelium.

Animals↗
PubMed1985

The distribution of the Simulium damnosum complex in Sierra Leone and its relation to onchocerciasis.

Because of the paucity of literature concerning onchocerciasis and its vectors in Sierra Leone, new information of the geographical distribution of the Simulium damnosum complex is presented in the context of a comprehensive review of what is known generally about S. damnosum s.l. in Sierra Leone, and how the data relate to the transmission of onchocerciasis. Neither biting adults nor breeding sites have been found on the coastal plain and Freetown peninsula, and these area seem to be free from infestation. Throughout the rest of the country S. damnosum s.l. breeds extensively in all the major river systems. The close proximity of the major rivers to one another facilitates inter-river migration, and ensures that most villages are well within the fly's dispersal range. In accordance with this, onchocerciasis is widespread throughout Sierra Leone and vector biting has been recorded away from riverine breeding sites. Seven cytospecies have been recorded in Sierra Leone but of these S. sirbanum and S. damnosum s.str. are rare outside the far north, in the narrow savanna belt. Simulium squamosum and S. yahense are widely distributed, although S. squamosum is somewhat less common than S. yahense which unexpectedly occurs in large rivers of the forest and savanna as well as small forest streams. Simulium sanctipauli has been found in the south-east of the country, where the forest is most dense, whereas S. soubrense occurs farther north. A new species referred to as S. soubrense 'B' is restricted to the south and west of the country. Over most of Sierra Leone onchocerciasis shows a 'forest' epidemiology and is transmitted by 'forest' vector cytospecies. However, data from the narrow savanna belt in the extreme north are sparse.

Animals↗
PubMed1987

A taxa summary for the Simulium damnosum complex, with special reference to distribution outside the control areas of West Africa.

A synoptic list is provided of currently recognized taxa in the Simulium damnosum complex, with an indication of their geographical distributions. Outline maps are given for the distribution of S. damnosum sensu lato, and for the West African cytospecies of the complex. Short reports on the identities and distributions of member taxa are given for countries other than those of the Onchocerciasis Control Programme in the Volta River Basin (OCP) and its Senegambia Extension; these are mainly based on collation of published and unpublished data for the post-1976 period (since the last WHO Expert Committee Report on Onchocerciasis).

Africa↗
PubMed1987

Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon I. Prevailing Simulium vectors, their biting rates and age-composition at different distances from their breeding sites.

Along the main water courses in the sparsely populated areas of the Sous-Préfecture of Tcholliré, the vectors of onchocerciasis were mainly Simulium damnosum s. str. and S. sirbanum, together with a small proportion of S. squamosum. Over a period of one to three years, vector biting rates were measured at 23 fly-catching sites in the vicinities of nine villages with different endemicities of onchocerciasis. Annual Biting Rates (ABR) on man were estimated as 26,100-83,800 fly-bites per man per year along the rivers Mayo Rey and Vina du Nord, and 11,000-37,400 at rainy season tributaries. Biting rates decreased rapidly at increasing distances from the river, and were between 10,700 and 2400 at 2-10 km cross-country from the breeding site. Lowest biting rates (50-6000) were measured at the village centres. The ABR varied from year to year in relation to the water-discharge of the main rivers, the coefficient of variation of the mean being 34-49%. The parous rates were 64-73% at the perennial breeding sites and only 17-44% away from the breeding sites, indicating dispersal mainly of young nulliparous flies and a reduced flight-range after oviposition.

Age Factors↗
PubMed1987

Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon II. Seasonal and diurnal changes in the biting densities and in the age-composition of the vector population.

Near the perennial breeding sites in the main water courses the highest monthly biting rates were recorded from June to August (early rainy season) and again from December to February (dry season), but near the rainy season breeding sites in the affluents, or at fly-catching sites, more than 2 km inland from the nearest main river breeding site, the highest rates were recorded between August and December (mid-rainy to early dry season). The variation of the biting rates over the year depended on the waterflow of the main rivers and on the differential dispersal of the flies from the breeding sites during the dry and rainy seasons. At the beginning of the rainy season, when the rivers started flowing, an immigration of non-local flies was observed at the river Mayo Rey near Tcholliré, presumably coming from Simulium breeding sites in the Adamaoua mountains to the South. During three years 77,374 flies were caught by daily catches between 06.00 and 18.30 hours. During the dry season the biting activity of nulliparous and parous flies was highest between 09.00 and 10.00 hours and 16.00 and 17.00 hours, 9% and 22% of the total day-catches respectively. In the rainy season the peak biting rates occurred between 06.00 and 07.00 hours (9%) and again from 16.00 to 17.00 hours (14%). The lowest biting rates were observed between 11.00 and 12.00 hours in both dry and rainy seasons (4% and 3% of the total catch). Nulliparous flies showed higher variations in biting activity than did parous flies, leading to the highest proporation of parous flies during midday.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1987

Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon III. Infection rates of the Simulium vectors and Onchocerca volvulus transmission potentials.

Populations of Simulium damnosum s.str. and S. sirbanum were examined for infections with filarial parasites during three years in the areas of Tcholliré and Touboro, at sites at different distances from Simulium breeding rivers, and in relation to villages with different endemicities of onchocerciasis. A total of 60,353 flies from 23 fly-catching sites were dissected. The overall infection rate was low, 11.8% of 35,357 parous flies dissected. 1681 flies (4.8% of the total parous) contained 3557 infective larvae, 68.8% of which were morphologically indistinguishable from Onchocerca volvulus and 31.2% were infective 'Type D' larvae of non-human origin, indicating a high degree of zoophily of the fly populations. It was estimated that only 20-40% of all bloodmeals were taken from man. The majority (54%) of all infective O. volvulus larvae were found in the heads of the flies, the remainder being in the thorax (34%) and abdomen (12%). Only 54% of the O. volvulus infective larvae left their vectors during a bloodmeal which, however, was not completed in most cases. During the rainy season infection rates with O. volvulus infective larvae were 3.5% of the total parous flies, as compared with 1.8% during the dry season. The average number of infective larvae of O. volvulus per infective fly was 2.6 and 2.2 during the rainy and dry seasons respectively. These variations in the vectorial efficiency of the fly populations, as well as variations from one site to another, could be explained by different survival rates and man-biting habits of the various vector populations during the dry and rainy seasons and in different regions, rather than by different endemic profiles of onchocerciasis in the human population. The intensity of transmission varied seasonally and was highest (1609 to 3076 infective larvae/man/year) near the main breeding sites, where transmission was almost perennial. At distances of more than 3 km from the river transmission was mainly restricted to the rainy season and the Annual Transmission Potential was below 200, whereas low to zero levels of transmission were measured inside villages more than 3 km distant from the river. The coefficient of variation of the Annual Transmission Potentials over the three years of studies was from 31% to 192% of the mean, being higher that the variations in the corresponding levels of the biting rates, due to the low numbers of infective flies dissected at sites with low transmission.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon IV. The different exposure to Simulium bites and transmission of boys and girls and men and women, and the resulting manifestations of onchocerciasis.

The sojourn times of the human population were monitored over one year at 12 sites in the vicinity of three villages in the Cameroon Sudan-savanna, where the Onchocerca volvulus transmission potentials had been measured one year previously. Boys stayed longer outside the villages, and were exposed 2.1 to 2.7 times more than girls to transmission of onchocerciasis, whereas the exposure of men was similar or only moderately higher than the exposure of women. In boys, the onset of infections and ocular lesions was earlier and the average microfilarial density at the buttock (2.2, 9.4 and 79.3 mff snip-1) was much higher than in girls (0.1, 5.8 and 42.2 mff snip-1 at the three villages respectively). These differences were maintained in the adult population, where the average microfilarial density was 52.3, 80.4 and 183.1 mff snip-1 in men and 15.6, 49.6 and 114.7 mff snip-1 in women. Ocular lesions due to onchocerciasis were found in 5, 13 and 55% of the male population in the three villages, as compared with 2, 3 and 8% of the female population. There was a close relationship between the degree of exposure to the transmission of disease and the resulting microfilarial load in the skin which was not different for the two sexes, and a similar trend was seen for the occurrence of ocular lesions due to onchocerciasis. The influence of an early and heavy infection on the evolution of disease manifestations is discussed.

Age Factors↗
PubMed1987

Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon V. What is a tolerable level of Annual Transmission Potential?

The prevalence and intensity of infection with Onchocerca volvulus were assessed in population surveys in nine villages, situated at different distances from Simulium damnosum s.l. breeding sites. The prevalence varied from 48 to 89%, the arithmetic mean densities of microfilariae per skin snip were between 16 and 109, and severe ocular lesions were found in from 1 to 22% of patients. Annual Transmission Potentials (ATP) were measured for up to three years in the near vicinity of nine villages at several fly-catching sites. Weighted means of the ATP over the three years, and of the sojourn times of the human population, were calculated at three of the villages, where the prevalence of onchocerciasis was 51, 61 and 89%. An average ATP of 100 larvae or less in the head, thorax and abdomen of the flies was associated with an onchocerciasis prevalence of 50 to 60%, a mean microfilarial density below 40 microfilariae per skin-snip, less than 5% of ocular lesions, and no onchocercal blindness. This value might therefore be considered to be an indication of the level to which the transmission must be reduced in the savanna in order to prevent the occurrence of severe ocular lesions or blindness. It is lower than the present level accepted by the Onchocerciasis Control Programme in the Volta River Basin.

Animals↗