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 793 records · Page 44Linked to original sources
PubMed1989

Simulium (Edwardsellum) squamosum kitetense ssp. n., a new chromosomal and morphological subspecies within the Simulium damnosum complex from east Zaire.

A new subspecies within the Simulium damnosum complex is described from the Lualaba river, East Zaire, on the basis of polytene chromosome analysis and larval morphology, under the name Simulium (Edwardsellum) squamosum kitetense ssp. n. Chromosomally it is most similar to S. squamosum, from which it differs by three new fixed inversions. Morphological differences include a reduced number of rays on the premandibular fans, the particular aspect of the combs on those rays, and the general colour of the body which is a very light yellow. A second population from a nearby river was morphologically and chromosomally quite different, although more samples are needed to clarify its taxonomic position.

Animals↗
PubMed1989

On the possibility of bovine Onchocerca species infecting Simulium damnosum s.l. in the forest zone of Sierra Leone. I. Parasitological aspects.

As part of a study to assess to what extent Onchocerca-like infections in S. damnosum s.l. in the forest zone of Sierra Leone were likely to be of bovine origin, Onchocerca infections were studied by post mortem examination of cattle killed at Bo abattoir and by examination of skin biopsies from cattle born and reared at Njala, in the forest zone, and Musaia, in the savanna zone. Post mortem studies of 45 cattle which had originated from northern Sierra Leone and Guinea revealed a prevalence of infection with microfilariae (mff) of O. gutturosa of 87%, O. ochengi 18% and O. armillata 7%. Examination of indigenous cattle revealed transmission of O. gutturosa in both forest (Njala) and savanna (Musaia) areas, and age prevalence analysis at Njala indicated a high intensity of transmission. Autochthonous transmission of O. armillata occurred at Njala at low intensity. Onchocerca gutturosa from Sierra Leone resembled U.K. isolates of O. gutturosa in terms of glucose phosphate isomerase electrophoretic mobility and acid phosphatase activity of in situ-stained mff. Hide mapping of O. gutturosa revealed skin concentrations of mff dorsally at the withers area and also ventrally at the dewlap, brisket and upper forelegs. It was concluded that only O. gutturosa was transmitted at high intensity to cattle in the forest zone of Sierra Leone. Hence, subsequent studies were directed towards determining the vector of O. gutturosa.

Animals↗
PubMed1990

The onchocerciasis focus at Kinsuka/Kinshasa (Republic of Zaire) in 1985. I. Entomological aspect.

The entomological aspect of the onchocerciasis focus at Kinsuka/Kinshasa has not been studied since vector control was carried out in 1948. As in 1940, larvae of Simulium damnosum s.l. are located in the arm of the Zaire River flowing between Mimosa Island and the Zairian bank. They are, however, scarce. Cytotaxonomic studies showed that the S. squamosum group was the only member of the S. damnosum complex present in the region of Kinshasa. Physico-chemical analysis of the water at breeding sites determined that S. squamosum larvae develop in neutral or acid water with a conductivity of less than 50 micronhos cm-1 and a low concentration of dissolved salts. Longitudinal study showed that the 'annual biting rate' (ABR) and the 'annual transmission potential' (ATP) fluctuate from 2406-5999 bites man-1 year-1 and from 120-236 infective larvae man-1 year-1 respectively. The low transmission rate at Kinsuka is mainly due to the low level of the biting population occurring during the main river rising. The increase in Kinsuka's population has reinforced this situation by 'diluting' the parasite in the human reservoir.

Animals↗
PubMed1990

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 significantly higher than the number caught at riverside sites. Infective flies were caught only in farmland and only during the early rainy season. The combined Annual Transmission Potential for the five sites was 129 larvae per man per year. Isoenzyme electrophoresis and morphology of biting flies identified the S. sanctipauli/soubrense subcomplex as the most common vector species. Simulium yahense and S. squamosum were sometimes present. It was concluded that the classical riverside monitoring sites do not represent high risk areas for the transmission of onchocerciasis in a forest village sited well away from the main S. damnosum s.l. breeding sites. The highest risk areas are in open farmland.

Animals↗
PubMed1990

The transmission of onchocerciasis at a forest village in Sierra Leone. II. Man-fly contact, human activity and exposure to transmission.

In the first of these papers we reported on the biting-densities of Simulium damnosum s.l., vector of onchocerciasis, at sites in and near to a village in the forest area of Sierra Leone that was well separated from any large Simulium breeding river. It was found that biting-densities and transmission levels were higher in open farmland than at riverside sites. In this paper we examine the relative time spent by the villagers at the same five sites in and near to the village of Baoma Lungibu, and compare the time spent and activity, with known Simulium biting-densities and transmission indices. It is concluded that, in this situation, the highest risk of infection with onchocerciasis was to persons of either sex in the 20-39 age group who were engaged in farming, or travelling through open farmland, during the months of June to August at the beginning of the wet season. Activities in and close to the village, even by the riverside, where shade cover was heavy, presented little risk of infection.

Adolescent↗
PubMed1991

Freshwater crabs and Simulium neavei in east Africa. III. Morphological variation in Potamonautes loveni (Decapoda: Potamidae).

Potamonautes loveni (Colosi) is the valid name for the species also described as P. granviki, P. harvardi and P. loveni longimerus, and incorrectly identified as P. berardi berardi. Potamonautes jeanelli and P. idjwiensis may be allied to P. loveni, but are geographically separated and show sufficient morphological distinction not to be considered conspecific. Potamonautes loveni occurs in the upper reaches of rivers on the highlands of western Kenya and eastern Uganda. Its replacement by other species, principally P. niloticus, at lower altitudes is probably determined by the temperature range of the water. Potamonautes loveni has been observed to coexist with P. niloticus within the range of altitude 1280-1950 m. Distinct forms of P. loveni, differing in colour, size and the expression of the post-frontal crest, occur on the western side of Mt. Elgon and in the former ochocerciasis foci of Kenya. Hybridization is evident in populations from between these areas. Morphological divergence within P. loveni may be the result of past climatic change. Periods of generally lower temperature have been accompanied by increased aridity and reduction of forest cover. It is suggested that these conditions are such as to promote a disjunct distribution of P. loveni, and in particular the isolation of the Mt. Elgon population.

Animals↗
PubMed1991

The development of Onchocerca dukei and O. ochengi microfilariae to infective-stage larvae in Simulium damnosum s.l. and in members of the S. medusaeforme group, following intra-thoracic injection.

Neonate Simulium females from an endemic area of human and bovine onchocerciasis in North-Cameroon were injected in one set of experiments with microfilariae (mff) of Onchocerca dukei and in another with mff of O. ochengi. Onchocerca dukei was found to develop to infective third-stage larvae in Simulium flies: 148 third-stage larvae (28.1% of injected mff) were recovered in S. hargreavesi, seven (10.4% of injected mff) in S. vorax, and 12 (1.3%) in S. damnosum s.l. Onchocerca ochengi mff developed in S. hargreavesi at a rate of 17.3% and in S. damnosum s.l. at 16.1%, yielding a total of 77 and 32 third-stage larvae respectively. Onchocerca dukei infective larvae had a mean length of 717.3 microns and a mean maximum diameter of 17.5 microns, and were slightly shorter and conspicuously thinner than those of O. ochengi (748.3 microns x 20.4 microns). All larval stages of O. dukei typically had an attenuated anterior end. The implications of these findings for the epidemiology of human onchocerciasis are discussed.

Animals↗
PubMed1991

Studies on onchocerciasis in forest-savannah mosaic areas of Nigeria. I. Investigations in Gbaragu, Oji River.

Reports on onchocerciasis in Nigeria have been scanty, despite the size of the country and of the problem. A survey of the prevalence and transmission of the disease in the south-eastern communities of Nigeria was commenced, with a year-long study of the vector and the clinical manifestations of the disease in a forest-savannah mosaic area on the Oji river. Microfilaraemia was found in 76% of the population, and nodules in 62%; there were no significant differences between male and female prevalence rates. Skin and ocular lesions of onchocerciasis, including 'Sowda', were common. Flies of the Simulium damnosum complex were found breeding along the entire length of the Oji river and tributaries. Biting occurred all the year round, but peaked in the months of March, April and May.

Adult↗
PubMed1993

Description of a computer model of forest onchocerciasis transmission and its application to field scenarios of vector control and chemotherapy.

This paper describes a computer simulation model for onchocerciasis (SIMON). Using epidemiological and entomological data from a specific hyperendemic village in the forest area of Sierra Leone, the model is used to examine the effect of vector and chemotherapeutic control strategies, both separately and in combination, as well as the risk to an uninfected population caused by immigrant, infected Simulium damnosum and humans. The model suggests that, in this village, the human population of about 420 requires an average annual input of about 200 mature fecund, female Onchocerca volvulus per year to maintain a skin-snip prevalence of just under 70%. SIMON also predicts that 99% effective vector control would lead to eradication of all adult worms in 18 years, and that abandoning control before 14 years could lead to recrudescence. Chemotherapy with ivermectin at six-month intervals reaching 90% of eligible persons (effective 66%) might take 29 years to achieve eradication because of continuing transmission, particularly in the early years, but it would probably be possible to abandon treatments after 18 years because the residual worm population would no longer be self-sustaining. Combined ivermectin and vector control, both at reduced levels, could be as effective as 99% vector control. Immigrant infected flies are likely to pose a greater threat to an uninfected human population than small numbers of infected persons. The model suggests that, at levels of infection undetectable by skin-snip, the parasite could linger in the human population for 30 or more years sustained by sporadic transmission.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Criteria for the selection of larvicides by the Onchocerciasis Control Programme in west Africa.

One of the weekly decisions the Onchocerciasis Control Programme has to make, in its operations in 11 west African countries, is the selection of one insecticide out of the six used that is most appropriate to the river stretches to be treated. This decision depends on several criteria, linked not only to the compounds themselves but also the hydrological conditions and blackfly populations involved. Given the great number of breeding sites (gites) to be treated, in 23,000 km of rivers at the height of the rainy season, this paper identifies the parameters needed to facilitate the choice of insecticide and to optimize the larviciding in terms of cost effectiveness, management of resistance and minimizing the environmental impact.

Africa, Western↗
PubMed1993

Analysis of survival data for Simulium damnosum using the regression method.

The survival data (under laboratory conditions) for blackfly (Simulium damnosum) are analysed using Cox's proportional hazard model, and an accelerated life model assuming a Weibull baseline survival function. The results show that allowing for the numerical density of microfilariae uptake is important as a covariate term in the Cox's model. High values of the covariate significantly reduce the chances of survival of the fly. The appropriate explicit expression for the survival function obtained can explain the low proportion of infective flies observed in the field.

Animals↗
PubMed1994

A rapid mapping technique for the prevalence and distribution of onchocerciasis: a Cameroon case study.

A rapid and cheap method for mapping the endemicity levels of onchocerciasis in both forest and savanna areas, where the vectors are members of the Simulium damnosum complex, is described. The selection of the study communities is based on a general understanding of the vectors' ecology and biassed towards those at highest risk of onchocerciasis, although there must be adequate geographical coverage. In a case study in Cameroon, prevalences were determined, using the non-invasive nodule palpation technique, in samples, each of 30-50 adult males, from 49 villages in six study areas in Cameroon. The method proved effective in the rapid mapping of onchocerciasis distribution in all areas studied, in which the distribution patterns varied from the classical linear to diffuse, and in one area with an anomalous distribution. The method should prove of value in the design of national onchocerciasis control programmes.

Adult↗
PubMed1997

Successful control of onchocerciasis vectors in San Vicente Pacaya, Guatemala, 1984-1989.

Between 1984 and 1989, the onchocerciasis-vector control zone on the pilot area of San Vicente Pacaya, Guatemala, which had been subject to experimental control since 1979, was extended from 91.3 to 148.6 km2. Temephos was used as a larvicide against Simulium ochraceum s.l. the target species. As a new strategy, only breeding sites with water discharges of 0.1-10 litres/s were treated, every 2 weeks. This approach provided a substantial reduction in effort, number of treated sites, time and cost. To assess the effect of the temephos, nine sites were selected in which standardized collections of adult Simulium were made twice a month, by human bait. There was an obvious difference between the pre- and post-control mean densities of flies at each site. In the northern area, which includes the Lavaderos, Barretal, Colina and Rodeo sites, the biting density in 1979, before treatment, varied between 10 and 64 flies/man-hour (FMH). Four years later, this had been reduced to 0.1-3.2 FMH, and by the end of the present study, in 1989, the mean density was zero FMH. In the southern area, which lies south-east of Lavaderos (and includes Guachipilin, Ingerto, Pena Blanca and Sierra Morena), the density during the pre-control phase was 24 FMH at one of the two sites investigated at the time and 39.3 FMH at the other. It fell to 0.1-0.5 FMH after 5 years of control and to zero (three sites) or close to zero (< or = 0.5 FMH; one site) for the last 4 years of the present study. To assess the effect of vector control on onchocerciasis prevalence and incidence, 1280 residents from six endemic communities, out of 12,000 permanent inhabitants, were examined. In Santa Cruz, Patrocinio and Los Rios, the prevalence of skin microfilariae in the subjects from each community fell from 8.1%-37.8% during the pretreatment, base-line period to 0.0%-31.5% when the study foci were totally integrated into the vector-control operation following treatment. Incidence among children (aged < or = 9 years) varied from 0%-25% for the period 1982-1984 but, thereafter, not a single case appeared in four of the six study communities (Santa Cruz, Patrocinio, Los Rios and Berlin). Incidence in Guachipilin did not decline appreciably, probably because of human migration into the area from other onchocerciasis foci. The prevalence of nodules followed a similar trend to those of the prevalence and incidence of skin microfilariae, falling from 9.1%-45.0% pre-control to 1.8%-14.3% 10 years later.

Animals↗
PubMed1998

Onchocerciasis: the burden of disease.

The greatest burdens related to human onchocerciasis are the result of the eye and skin lesions and severe itching produced by the microfilariae. Although the major manifestations of the disease do show geographical variation (e.g. onchocercal blindness is not a common complication in all endemic countries), they are often sufficiently severe to prevent human use of the often very fertile land close to the rivers in which the vectors breed. Though for many years thought to be of relatively minor importance compared with onchocercal eye disease, the skin lesions of onchocerciasis have recently been shown to be a major socio-economic burden, in terms of disability-adjusted life-years. The demonstration of an excellent correlation between the prevalence of palpable nodules in a community and the community microfilarial load has led to the development of rapid, safe and non-invasive methods to assess and map the levels of endemicity across whole countries. This has enabled mass treatment with Mectizan (ivermectin, MSD) to be targeted first at hyperendemic communities. Estimates of the burden of onchocerciasis will continue to change as better means of measurement become available. It seems possible, however, that use of Mectizan will eliminate the disease before its true burden can be estimated accurately.

Adolescent↗
PubMed2001

Eliminating onchocerciasis after 14 years of vector control: a proved strategy.

From 1976 through 1989, weekly aerial spraying operations against blackflies were carried out along the rivers of a wide savanna area of West Africa (approximately 700,000 km(2)) where onchocerciasis was hyperendemic. The level of endemicity began to decrease significantly after 4 years of vector control and became very low in 1989. This situation has been maintained without any vector control activity or chemotherapy, and no incidence of any new cases has been detected. An ophthalmological study carried out in 2000 has confirmed these good results, showing only cicatricial ocular lesions in the examined population. These results led to the conclusion that 14 years of vector control may achieve long-term elimination of onchocerciasis, even in the absence of chemotherapy, provided that the treated areas are not subjected to any contamination by exogenous parasites carried in infected humans or flies.

Adult↗