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At least 865 records · Page 48Linked to original sources
PubMed2004

Long-term, large-scale biomonitoring of the unknown: assessing the effects of insecticides to control river blindness (onchocerciasis) in West Africa.

The control of river blindness (onchocerciasis), a human disease transmitted by black flies, has been an economic and public health success in West Africa. It involved insecticide applications to as many as 50,000 km of rivers, almost weekly, in 11 countries between 1974 and 2002. The long-term biomonitoring of the effects of insecticide use on the nontarget invertebrate (primarily insect) and fish communities was initially designed on the basis of limited knowledge available for West African rivers and on information from other areas. Routine monitoring surveys demonstrated little effect on fish but produced inconclusive results for invertebrates. Research conducted beyond these surveys and current views in river and general ecology indicate that permanent damage to invertebrates from insecticiding was unlikely. The scientific progress made during the 29 years of this biomonitoring program is relevant to future, large-scale, long-term programs worldwide.

Africa, Western↗
PubMed2003

Experimental studies on the transmission of Onchocerca volvulus by its vector in the Sanaga valley (Cameroon): Simulium squamosum B. Intake of microfilariae and their migration to the haemocoel of the vector.

As large-scale ivermectin distribution is becoming the mainstay of onchocerciasis control in Africa, the issue of its impact on local transmission is increasing in importance. The vector competence of Simulium squamosum B in the severe focus of the Sanaga valley, Cameroon, was therefore investigated, by feeding 1320 flies on 14 carriers of Onchocerca volvulus microfilariae (mff). The results enabled the relationships between skin microfilarial load, microfilarial intake by the flies, the proportion and mean number of ingested mff that succeed in reaching the fly's haemocoel, and the frequency distribution of the ingested mff to be described, as functions of time post-engorgement (p.e.) and parasite density (while taking account of possible measurement error in the predictor variable). The proportion of flies with haemocoelic mff and the mean number of mff/fly increased up to 3 h p.e. The proportion of flies with ingested mff was non-linearly related to mean intake, via the negative-binomial distribution, with the overdispersion parameter k best described as an increasing (power) function of the mean. Approximately one in every three ingested mff escaped imprisonment by the peritrophic matrix, irrespective of the skin microfilarial load or the intake of mff. The relationship between successful and input mff is nearly linear (indicating proportionality) in S. squamosum B. These results are compared with those from O. volvulus-S. damnosum s.l. combinations in other West African foci.

Adolescent↗
PubMed2006

Towards the elimination of onchocerciasis.

Human onchocerciasis is a severely disabling filarial disease that is endemic in 28 African countries, six Latin American countries and Yemen. The disease causes a high burden of blindness and visual loss, along with itching and other severe dermal manifestations. It constitutes a significant obstacle to socio-economic development in highly endemic riverine areas, where the Simulium blackflies that act as vectors breed. Onchocerciasis has been subject to control efforts for more than 50 years, initially mainly through vector control but since 1988, with free access to ivermectin (Mectizan), also through large-scale chemotherapy. The Onchocerciasis Control Programme in West Africa operated successfully from 1974 to 2002 in 11 countries, covering the worst savannah foci of the disease through vector control and, in its later stages, also through ivermectin distribution. The African Programme for Onchocerciasis Control was established in 1995, to cover the remaining endemic areas in Africa, with the sustainable annual distribution of ivermectin by 2010 its main goal. Meanwhile, the Onchocerciasis Elimination Program for the Americas is making rapid progress in the virtual regional elimination of the disease through ivermectin distribution, which is achievable primarily because the vectors in the western hemisphere are less efficient than those elsewhere. The global elimination of onchocerciasis as a public-health problem is now within reach but this will require long-term strategies to secure the great gains made so far, through ivermectin treatment and local vector control. Research is needed to define the optimal approaches with the existing tools and to intensify the development of alternative strategies, such as macrofilaricidal drugs for wide-scale use.

Africa↗
PubMed2002

Ecdysteroids and oocyte development in the black fly Simulium vittatum.

BACKGROUND: Oocyte development was studied in the autogenous black fly, Simulium vittatum (Diptera, Nematocera), a vector of Onchocerca volvulus, the causative agent of onchocerciasis. RESULTS: Oocyte growth was nearly linear between adult eclosion and was complete by 72 hours at 21 degrees C. The oocyte became opaque at 14 hours after eclosion indicating the initiation of protein yolk deposition. The accumulation of vitellogenin was measured using SDS-PAGE. The density of the yolk protein bands at about 200 and 65 kDa increased during the first and second days after eclosion. The amount of protein in the 200 kDa band of vitellogenin, determined using densitometry, rapidly increased between 12 and 25 hours after eclosion. Ecdysteroid levels were measured using a competitive ELISA. Ecdysteroid levels increased rapidly and subsequently declined during the first day after eclosion. CONCLUSION: These data show a correlation between the appearance of vitellogenin in the oocyte, and the rise in ecdysteroids. A possible relationship to molting of the nematode, Onchocerca volvulus, is discussed.

Animals↗
PubMed1998

Analyses of cDNA and recombinant protein for a potent vasoactive protein in saliva of a blood-feeding black fly, Simulium vittatum.

A cDNA was cloned from the salivary glands of a blood-feeding black fly Simulium vittatum. The encoded protein has been given the name Simulium vittatum erythema protein or SVEP, because of its ability to increase blood perfusion in skin capillaries, resulting in the well-characterized erythema of black fly bites. The full-length cDNA contains 548 base pairs which encode 152 amino acid residues of the nascent protein. Post-translational processing produces a mature, secreted protein of 133 residues with a molecular mass of 15.4 kDa. Recombinant SVEP (rSVEP) was produced in a baculovirus expression system and purified by a one-step reversed-phase HPLC procedure. Analyses of physical properties and biological potency demonstrated fidelity of rSVEP to the native protein. Recombinant SVEP relaxed rabbit aorta preparations when preconstricted with 2 micromol l-1 phenylephrine or 25 mmol l-1 K+ but not with 60 mmol l-1 K+. Further, the rSVEP-induced relaxation response of phenylephrine-constricted aorta was inhibited by glibenclamide (10 micromol l-1), suggesting that at least part of its action to relax smooth muscle may result from the opening of ATP-dependent K+ channels. SVEP is a novel salivary-gland-derived vasoactive protein that may be essential for blood feeding by black flies and could potentially enhance transmission of filarial parasites.

Amino Acid Sequence↗
PubMedDate not supplied

[Mansonella ozzardi in the Federal Territory of Roraima, Brazil. Distribution and finding of a new vector in the area of Surumu River].

A survey conducted among the Makuxi Indians from 15 settlements in the northeastern part of the Territory of Roraima, Brazil, revealed the occurrence of Mansonella ozzardi in 3,2% (21/652) of the persons examined. The absence of demonstrable infection--with one exception--in persons under 15 years of age, and the low microfilaria density in adults suggest that mansonelliasis has been acquired by the Makuxi Indians outside their villages. As many Indians from the region pan gold on the Upper Maú (Ireng) river--where black flies occur in great quantity--the mining camps are probably the sites of transmission. Experimental infection with M. ozzardi of Simulium oyapockense s.l. (or Simulium roraimense) showed that this species, at the least in the Surumu river area, is capable of supporting the full development of the microfilariae. Although S. oyapockense has a wide distribution in the extreme north of Brazil, it does not appear to be an efficient vector, since only 20,6% (19/92) of the specimens collected after a blood meal on a naturally infected Indian contained larval stages of M. ozzardi (with an average of 1-2 larvae per fly). The high prevalence rate of infection found, in a previous survey, among the Sanumá and Mayongong, two Indian groups living at the Auaris river area, on the other side of the Territory of Roraima, indicates that a more competent intermediate host should exist in that region.

Animals↗
PubMedDate not supplied

Methods for field detection of resistance to temephos in simuliids. Larval esterase level and topical application of the insecticide to adults.

Two practical field methods for indirect detection of simuliid populations resistant to temephos are proposed. The first is based on high esterase activity in resistant larvae and involves adaptations of a filter paper test in which faintly stained spots indicate susceptible populations and strongly stained ones reveal populations resistant to temephos. The second is based on the resistance to the larvicide when adults are topically exposed, and involves the use of diagnostic doses obtained by the comparison between the LD50 for susceptible and resistant populations. The relevance of such methods is discussed in order to help resistance detection in Simulium pertinax Kollar control programmes.

Administration, Topical↗
PubMedDate not supplied

Onchocerciasis in Ecuador: the situation in 1989.

Details are given of the prevalence rates of onchocerciasis from the most recent surveys (1989) conducted in northern Ecuador. The disease has intensified and dispersed considerably due to migration of infected individuals and the presence of a highly efficient vector. Comparison of these data with those from two previous surveys carried out in 1982/83 and 1986 and correlated with entomological findings highlight the danger of the formation of new foci of onchocerciasis in areas currently free of the disease. Recommendations are made for further entomological studies in areas either recently or likely to be affected by the disease where potential vectors are unknown or different to those registered in the Santiago focus. Ivermectin treatment with local vector control in specific areas is advocated to reduce the disease to a low level of public health importance.

Animals↗
PubMedDate not supplied

Biological control program against simuliids in the State of São Paulo, Brazil.

In Brazil, the use of biological vector-control methods has been largely confined to experimental research, with little or no application of such techniques by public institutions responsible for implementing control programs. The notable exceptions have been the black fly control program carried out by the Health Secretariat in the State of São Paulo. Since the 1980s, São Paulo's "Superintendência de Controle de Endemias" has been conducting studies on the viability of using Bacillus thuringiensis (H-14) for simuliid control, and the results have been so encouraging that the agency has now incorporated this method into its Simuliid Control Program.

Animals↗
PubMed2000

Mosquitocidal bacterial toxins: diversity, mode of action and resistance phenomena.

Bacteria active against dipteran larvae (mosquitoes and black flies) include a wide variety of Bacillus thuringiensis and B. sphaericus strains, as well as isolates of Brevibacillus laterosporus and Clostridium bifermentans. All display different spectra and levels of activity correlated with the nature of the toxins, mainly produced during the sporulation process. This paper describes the structure and mode of action of the main mosquitocidal toxins, in relationship with their potential use in mosquito and/or black fly larvae control. Investigations with laboratory and field colonies of mosquitoes that have become highly resistant to the B. sphaericus Bin toxin have shown that several mechanisms of resistance are involved, some affecting the toxin/receptor binding step, others unknown.

Animals↗