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At least 811 records · Page 45Linked to original sources
PubMed1990

The predicted and observed decline in onchocerciasis infection during 14 years of successful control of Simulium spp. in west Africa.

In 55 villages from the well-protected central area of the Onchocerciasis Control Programme in West Africa (OCP), skin snip surveys have been carried out at regular intervals since the programme started, and the latest round of surveys was undertaken after 12-14 years of successful vector control. The observed trends in the prevalence and intensity of onchocerciasis infection in cohorts of adults were compared with the trends predicted using a host-parasite model. After 12-14 years of control the community microfilarial load (CMFL) was close to zero in all villages. During the last few years of control, the prevalence of infection declined at an accelerated rate, and this was predicted by the model. There was generally good agreement between observed and predicted trends. The predictions were based on an estimated average duration of infection of 10.4 years, which corresponds to a mean reproductive lifespan for Onchocerca volvulus of 9-9.5 years, and an upper limit of 15 years for 95% of the infections. Differences between the observed and predicted data included the trend in CMFL between the first and second surveys, which in 18 villages did not show the predicted decline. Furthermore, the observed final decline in prevalence was faster than predicted in the north-eastern part of the central OCP area. After 14 years of vector control, the level of onchocerciasis has fallen to such a low level that consideration is being given to ending larviciding.

Adult↗
PubMed2004

Black fly involvement in the epidemic transmission of vesicular stomatitis New Jersey virus (Rhabdoviridae: Vesiculovirus).

The transmission routes of Vesicular stomatitis New Jersey virus (VSNJV), a causative agent of vesicular stomatitis, an Office International des Epizooties List-A disease, are not completely understood. Epidemiological and entomological studies conducted during the sporadic epidemics in the western United States have identified potential virus transmission routes involving insect vectors and animal-to-animal contact. In the present study we experimentally tested the previously proposed transmission routes which were primarily based on field observations. Results obtained provide strong evidence for the following: (1) hematophagous insects acquire VSNJV by unconventional routes while blood feeding on livestock, (2) clinical course of VSNJV infection in livestock following transmission by an infected insect is related to insect bite site, (3) infection of livestock via insect bite can result in multiple transmission possibilities, including animal-to-animal contact. Taken together, these data significantly add to our understanding of the transmission routes of a causative agent of one of the oldest known infectious diseases of livestock, for which the details have remained largely unknown despite decades of research.

Animals↗
PubMed1992

Modern medicine versus an ancient scourge: progress toward control of onchocerciasis.

Control of human onchocerciasis has been problematic. Vector control is practical and effective in only a circumscribed region of West Africa. Even in this area, control depends on meticulous monitoring of the vector and associated parasite species and precise application of requisite larvicide on a regular basis. As an alternative to vector control, chemotherapy-based control has been revolutionized by the finding that ivermectin, a novel semisynthetic macrocyclic lactone, is acceptable for mass distribution at the community level and that it represents an effective means of disease control when given once yearly. Efforts are underway to develop a vaccine to prevent infection.

Animals↗
PubMed1989

Visual detection of microencapsulated insecticides with selective staining and scanning electron microscopy.

Selective staining with Sudan IV and methylene blue for light microscopy and scanning electron microscopy (SEM) were investigated to determine their potential for detecting and quantifying microencapsulated insecticides. Penncap-M (microencapsulated methyl parathion), Penncapthrin (microencapsulated permethrin), and Dyfonate (microencapsulated fonofos) were selectively stained with Sudan IV but not with methylene blue. Selective staining was not possible for Altosid SF-10 or SR-20 (microencapsulated methoprene) with either stain. Sudan IV enabled detection of some microencapsulated formulations in the digestive content of selected aquatic invertebrates and prepared contaminated pollen samples. Staining intensity with Sudan IV was greatest with acetone but capsular damage was high. A solvent ratio of 50:50 and 20:80 acetone/xylene minimized capsular collapse and maintained good staining intensity. The use of SEM for capsule identification and quantification depended upon the method of sample preparation: the slide smear method was superior to samples prepared by incision or microtomy. SEM was most suitable for investigation of formulations such as methoprene, for which selective staining was not possible. The chemical basis of staining with Sudan IV and potential application of both identification techniques are discussed.

Aedes↗
PubMed1996

Improvement of techniques for age grading hematophagous insects: ovarian oil-injection and ovariolar separation techniques.

After injection of oil into the oviduct of hematophagous Diptera, the ovarioles become completely separated from each other, allowing examination of a large number of undamaged ovarioles, an important advantage over other techniques for accurately determining the physiological age of mosquitoes. The technique has been simplified and improved, especially by using a sodium chloride-glycerol-formaldehyde mixture for mounting preparations, which are more convenient and permanent for examination of the ovarioles. The difficulties of using the technique, their possible causes, and possibilities for overcoming them are described. Similar results can be obtained with an alternative technique, the ovariolar separation technique, using strongly diluted Carnoy's solution, which leaves ovaries in a fixed condition. Both techniques can be used for several hematophagous dipteran groups.

Aging↗
PubMed1999

Population biology of human onchocerciasis.

Human onchocerciasis (river blindness) is the filarial infection caused by Onchocerca volvulus and transmitted among people through the bites of the Simulium vector. Some 86 million people around the world are at risk of acquiring the nematode, with 18 million people infected and 600,000 visually impaired, half of them partially or totally blind. 99% of cases occur in tropical Africa; scattered foci exist in Latin America. Until recently control programmes, in operation since 1975, have consisted of antivectorial measures. With the introduction of ivermectin in 1988, safe and effective chemotherapy is now available. With the original Onchocerciasis Control Programme of West Africa coming to an end, both the new African Programme for Onchocerciasis Control and the Onchocerciasis Elimination Programme for the Americas, rely heavily on ivermectin self-sustained mass delivery. In consequence, the need for understanding the processes regulating parasite abundance in human and simuliid populations is of utmost importance. We present a simple mathematical framework built around recent analyses of exposure- and density-dependent processes operating, respectively, within the human and vector hosts. An expression for the basic reproductive ratio, R0, is derived and related to the minimum vector density required for parasite persistence in localities of West Africa in general and northern Cameroon in particular. Model outputs suggest that constraints acting against parasite establishment in both humans and vectors are necessary to reproduce field observations, but those in humans may not fully protect against reinfection. Analyses of host age-profiles of infection prevalence, intensity, and aggregation for increasing levels of endemicity and intensity of transmission in the Vina valley of northern Cameroon are in agreement with these results and discussed in light of novel work on onchocerciasis immunology.

Adolescent↗
PubMed1988

Comparative toxicity of Bacillus thuringiensis var. israelensis crystal proteins in vivo and in vitro.

Bacillus thuringiensis var. israelensis crystal proteins were purified by FPLC on a Mono Q column to yield 130, 65, 28, 53, 30-35 and 25 kDa proteins. All the purified proteins killed Aedes aegypti larvae after citrate precipitation, but the 65 kDa protein was the most toxic. A precipitated mixture of 27 and 130 kDa proteins was almost as toxic as solubilized crystals. In assays against a range of insect cell lines, the activated form (25 kDa) of the 27 kDa protein was generally cytotoxic with the lowest LC50 values in vitro. By contrast, the activated forms of the 130 kDa and 65 kDa protoxins (53 kDa and 30-35 kDa proteins, respectively) were much more specific than the 25 kDa protein in their action on dipteran cells, and each showed a unique toxicity profile which, in the case of the 130 kDa preparation, was restricted to Anopheles and Culex cell lines.

Aedes↗
PubMed1989

Endemic pemphigus foliaceus (Fogo Selvagem): II. Current and historic epidemiologic studies.

This paper details current and historic epidemiologic features of Fogo Selvagem (Endemic pemphigus foliaceus) in Brazil. The following features are described. a) The disease occurs in endemic fashion in regions of Brazil within the states of Goias, Mato Grosso do Sul, Parana, Sao Paulo, and Minas Gerais. It appears that the disease is spreading toward the northwest and west, involving the states of Mato Grosso, Para, Maranhao, Rondonia, Acre, and Amazonas. b) People at risk are young peasants or children of either sex or any race exposed to the local ecology in rural areas of endemic states. Although the disease has been described in urban centers, these occurrences are rare. c) Fogo Selvagem commonly appears in wild areas being colonized and disappears as these areas become urbanized. d) The majority of patients live in close proximity to rivers and within the 10-15 Km flying range of mosquitos or black flies (such as Simulium). It is hypothesized that a black fly, Simulium pruinosum may be the vector that precipitates the disease. f) There is a significant number of Fogo Selvagem in family units where multiple, genetically related individuals are affected. g) Finally, autoantibodies against lupus-associated antigens are not present in the sera of patients with Fogo Selvagem. Clinical examination of the skin, and serologic screening for pemphigus autoantibodies are specific parameters that can be used in the search for the etiologic agents that lead to autoimmune disease of the skin. To identify and prove an etiologic agent for this well-characterized autoimmune disease would be of tremendous importance to the understanding of autoimmune skin diseases, and potentially other organ-specific autoimmune disorders.

Age Factors↗
PubMed1996

A survey of the prevalence of biting by the Blandford fly during 1993.

To assess the frequency of bites by the Blandford fly, a postal survey was carried out at the end of the 1993 biting season. Questionnaires were sent to a random sample of 1,500 people, selected from the lists of the two general practices in Blandford Forum, and satisfactory replies were obtained from 1203 (80%). Altogether, 194 (16%) of subjects reported one or more insect bites, during the 2-month season, that had led to skin swelling more than 2.5 cm across. Of these, more than a quarter had suffered associated systemic symptoms, in the form of fever or joint pain. One hundred and forty-nine had used medications for bites, 20 had consulted a doctor, and seven had taken time off work or school. Bites were more common in females (22%) than males (9%). This difference was due largely to a higher frequency of bites on the legs. Risk might be reduced substantially in women by wearing trousers, especially in those who spend a lot of time outdoors.

Adolescent↗
PubMed1993

Gut-specific genes from the black fly Simulium vittatum encoding trypsin-like and carboxypeptidase-like proteins.

In haematophagous insects digestion of the blood meal provides nutrients for survival and essential components for egg production. We have isolated and partially characterized two gut-specific genes from the black fly Simulium vittatum. Sequence analysis revealed that both are highly similar to digestive proteases, one to trypsins and the other to carboxypeptidases. RNA blot analysis indicates that the expression of these two genes is regulated in a sex-specific manner; when fed the same sucrose-based diet, expression in males is substantially lower than in females. In females, expression of both genes is strongly induced by a blood meal. At 6 h after the blood meal the trypsin-like gene product was immunolocalized to the midgut epithelium and to the outer layers of the peritrophic matrix.

Amino Acid Sequence↗
PubMed1995

The Simulium damnosum species complex: phylogenetic analysis and molecular identification based upon mitochondrially encoded gene sequences.

The DNA sequence of portions of the 16s rRNA and the NADH dehydrogenase subunit 4 (ND4) genes were used to determine phylogenetic relationships in the Simulium damnosum s.l. species complex. Results suggested that at least two major clades existed in the S. damnosum species complex, and that members of the S. damnosum s.l. species complex were not closely related to North American Simulium species. The sequence variability of the ND4 gene was exploited to develop a method to distinguish the sibling species of the S. damnosum s.l. species complex, based on directed heteroduplex analysis of PCR products derived from the ND4 gene. This method was capable of classifying the six sibling species into at least five groups.

Animals↗
PubMed1987

The Beffa form of Simulium soubrense of the S. damnosum complex in Togo and Benin.

The Beffa form of Simulium soubrense Vajime & Dunbar, a member of the S. sanctipauli sub-complex of the S. damnosum complex, was found breeding throughout rivers in the Togo-Benin Gap, as far north as 9 degrees 30'N. Its distribution changed with the season. In southern Togo there were seasonal fluctuations in the relative abundancies of the Beffa form and of S. damnosum/S.sirbanum. There was considerable temporal and regional variation in the frequencies of different colour morphs of adult flies. The flies in Benin tended to be darker. Infections with Onchocerca volvulus (Leuckart) appeared to be independent of the host's colour morph category. Larger flies harboured significantly more first stage Onchocerca larvae but no significant relations with fly size were found for second and third stage larvae.

Animals↗
PubMed1987

Management of insecticide resistance in control of the Simulium damnosum complex by the Onchocerciasis Control Programme, West Africa: potential use of negative correlation between organophosphate resistance and pyrethroid susceptibility.

1. Resistance of some populations of the Simulium damnosum complex to temephos (100-fold at the LC50 level), with degrees of cross-resistance to chlorphoxim (14-fold) and other organophosphate insecticides, follows intensive larvicidal control of S. damnosum s.l. in West African river systems since 1975 by the WHO Onchocerciasis Control Programme. 2. Larvae of at least three sibling species of the S. damnosum complex have become organophosphate-resistant: these are the forest species S. sanctipauli Vajime & Dunbar and the savanna species S. sirbanum V. & D. and S. damnosum Theobald sensu stricto. 3. Organophosphate-resistant S. damnosum s.l. larvae show increased susceptibility to some organochlorine and pyrethroid insecticides, especially to permethrin (up to 11-fold) and OMS 3002 (up to 17-fold), as compared with organophosphate-susceptible populations. 4. This differential susceptibility is reflected by increased pyrethroid efficacy in operational use for river treatments against organophosphate-resistant field populations of S. damnosum s.l. larvae. Treatment of 100 km of the lower Bandama River in 1985 showed that permethrin at the highly selective dosage of 10 min exposure to 0.01 mg/l caused reversion towards organophosphate-susceptibility of the target population of S. sanctipauli. This effect was less pronounced when the Comoe River was treated at the lower dosage of 0.005 mg/l for 10 min. 5. To overcome temephos-resistance, it is proposed that the most rational usage of currently available larvicides would involve the following annual sequence of treatments: Bacillus thuringiensis serotype H-14 when river discharge is below 75 m3/s; chlorphoxim for about eight weekly treatment cycles after river discharge rises; permethrin (or alternative pyrethroid) for up to six treatment cycles--this should eliminate any incipient selection for chlorphoxim-resistance; resume chlorphoxim (or perhaps carbosulfan) treatments until river discharge falls below 75 m3/s permitting resumed use of B.t. H-14.

Africa, Western↗
PubMed1987

Microdistribution of immature African blackflies resulting from water velocity and turbulence preferences.

1. The velocity preferences of larval and pupal blackflies were studied experimentally by comparing the colonization of plastic strings placed in different velocity ranges; and also by investigating the simuliid microdistribution under natural conditions in the river. This required a novel method described for taking spot measurements of water velocity. 2. Simulium mcmahoni de Meillon, S. hirsutum Pomeroy and S. cervicornutum Pomeroy were most abundant in slow velocities (0.3-1.0 m s-1), S. colasbelcouri Grenier & Ovazza and S. hargreavesi Gibbins preferred 1.1-1.8 m s-1, S. squamosum Enderlein and S. vorax Pomeroy 1.9-2.2 m s-1. 3. The larvae of S. hargreavesi and S. cervicornutum preferred a higher velocity range compared with their pupae. 4. In moderate velocities (1.1-1.4 m s-1), the abundance of S. hargreavesi was greater under turbulent conditions than in smooth-flowing water, but this was reversed at very high velocities (2.3-2.6 m s-1). 5. Velocity had no apparent effect on substrate preference when substrates of different flexibilities were compared for three blackfly species. All avoided the most flexible substrates and preferred ones consisting of rigid articulating plates. Anisopteran predators were found to have a similar substrate choice.

Analysis of Variance↗
PubMed1987

Experimental hybridization between members of the Simulium damnosum complex.

Males of the Beffa form of Simulium soubrense Vajime and Dunbar were successfully crossed with female S.squamosum V. & D. and S.sanctipauli V. & D. Fertile eggs from both crosses were reared to larvae and, in the case of the Beffa x squamosum cross, to adults. Larval chromosomes from the Beffa x sanctipauli cross had normally paired homologues but those of the Beffa x squamosum cross showed extensive asynapsis and large heterozygous loops. The morphology of the larval and adult hybrids from the Beffa x squamosum cross were more characteristic of squamosum, but the adult males had scutal patterns typical of the Beffa form and retained this form's laboratory-mating propensity.

Animals↗
PubMed1987

The status of Simulium oyapockense and S. limbatum as vectors of human onchocerciasis in Brazilian Amazonia.

In an attempt to explain the current distribution of onchocerciasis in the forests of northern Brazil (Moraes et al., 1979, 1986), and its potential for dispersal to other areas, this study compares the vector status of Simulium oyapockense Floch and Abonnenc, 1946 in both a hypoendemic and an onchocerciasis free area with that of S. limbatum Knab, 1915 in the latter area. Both species allowed the full development of Onchocerca volvulus (Leuckart) to the infective L3 stage after experimental infection with microfilariae. Their vector competence was significantly lower than for other efficient vector species in South America and Africa because of the lethal effect of the cibarial armature on ingested microfilariae. The low vector capacity of S. oyapockense, together with the low prevalence and intensity of infection of O. volvulus, probably explains why onchocerciasis has not significantly increased in intensity over the last 10 years in the hypoendemic part of the Amazonian focus. Omnipresence of both vector species in the adjacent savanna region, however, could facilitate the spread of onchocerciasis if human population movements continue from the hyperendemic part of the onchocerciasis focus.

Animals↗