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PubMed1997

Do insecticide-treated curtains reduce all-cause child mortality in Burkina Faso?

To evaluate whether insecticide-treated netting (ITN) reduces child mortality in different epidemiological settings, 4 large, randomized, controlled trials were conducted in Africa. Here we report the findings from the trial in Burkina Faso, in an area of hyperendemic and markedly seasonal malaria transmission. The trial involved 158 villages, with a total population of some 90,000, grouped into 16 geographical clusters. Ascertainment of mortality among children aged 6-59 months began in early 1993. In June/July 1994, 8 of the clusters, randomly selected, received permethrin-treated curtains. Follow-up of children and ascertainment of mortality continued until May 1996. A 15% reduction in all-cause mortality among children aged 6-59 months was observed over the 2-year period following the installation of the curtains (95% c.i. -4% to 30%). In the first year, post-intervention mortality was substantially lower in the clusters receiving curtains compared with the control clusters (rate ratio = 0.74; 95% c.i. 0.57, 0.95) but in the second year, there was no difference between mortality in the two groups (rate ratio = 0.99). The overall two-year impact of the intervention is consistent with the impacts observed in other trials which have demonstrated reductions in child mortality of from 17% to 33%. However, the year-by-year analysis raises some concerns about the long-term effect of ITN. Further follow-up of this population is warranted.

Burkina Faso↗
PubMed1999

Control of malaria vectors: cost analysis in a province of northern Vietnam.

The cost of permethrin-treated bednets (50% EC; 0.2 g/m2, 2 rounds per year) was compared to the cost of residual spraying with lambdacyhalothrin 10% WP (0.03 g/m2, once yearly) in Hoa Binh, a mountainous province in northern Vietnam. Calculations of the amounts of insecticides needed were based on national guidelines, on data from a cross-sectional survey and on district activity reports. The actual cost of insecticide required per person per year was lower for impregnation (US$ 0.26) than for spraying (US$ 0.36), but the difference was smaller than expected. The total cost for impregnated bednets per person per year amounted to US$ 0.90 compared to USS 0.47 for spraying. The determining factor was the cost of the net, amounting to US$ 0.58 per person per year, assuming a 5-year life of the net. Other material (excluding nets), labour and transport combined, accounted for only 17% of the impregnation cost and 23% of spraying expenses. However, for the National Malaria Control Programme of Vietnam, the cost per person per year for impregnated bednets amounted to US$ 0.32 only, because the vast majority of nets are bought by the population. For spraying, the programme had to bear the entire cost.

Animals↗
PubMed1999

Control of zoophilic malaria vectors by applying pyrethroid insecticides to cattle.

The principal method of malaria control in South and West Asia--indoor residual spraying--is extravagant with insecticide. A more efficient way of deploying insecticide might be to apply it on livestock since the malaria vectors in the region are highly zoophilic. A series of investigations assessed the potential of cattle treated with pyrethroid to control zoophilic mosquitoes. Permethrin, deltamethrin, and lambdacyhalothrin were applied to cattle using a sponge at concentrations of 0.5 g/m2, 0.025 g/m2, and 0.025 g/m2, respectively. 'Whole animal' insecticide bioassays that simulated natural mosquito-host contact were used to measure insecticidal and behavioural effects on wild host-seeking mosquitoes. The bioassays were performed on both sheltered and outdoor grazing animals for up to 45 days post-treatment. The possibility that treatments might cause diversion of host-seeking vectors from cattle to people nearby was also investigated. At the doses tested deltamethrin had the most pronounced and longest-lasting effect, reducing the proportion of bloodfed survivors by over 50% for the first two weeks. The majority of mosquitoes affected by the insecticide were killed before feeding. Insecticidal impact was generally lower on grazing than on sheltered animals. There was no diversion of host-seeking mosquitoes from treated cattle to nearby humans at any stage after treatment. The application of insecticide to livestock using a campaign approach may prove an effective means of controlling malaria in the region. At the doses tested deltamethrin is the most appropriate insecticide for this purpose.

Administration, Topical↗
PubMed1999

A new strategy for treating nets. Part 1: formulation and dosage.

The conventional dosages of pyrethroid insecticides on mosquito nets assume that nets will be retreated at 6-12 month intervals. However, dosage should be related to washing of nets; if nets are only washed once or twice a year, their dosage requirements will be different to those which are washed fortnightly. A 'low-dose, frequent-wash' retreatment system might be technically more appropriate and more affordable where nets are washed frequently, as they are in Dar es Salaam. Moreover, for use as a domestic insecticide, water-based formulations of pyrethroid are preferable to the more commonly used emulsifiable concentrates (ECs). This paper reports laboratory evaluations of three formulations (ECs, Flowable, CS) of three pyrethroids (deltamethrin, lambdacyhalothrin, permethrin). Insecticidal activity was tested using serial bioassays at a range of dosages using Anopheles gambiae. The water-based formulations were no less effective than the ECs, even at the lowest dosages. Nets treated with 3 mg/m2 and then repeatedly washed and retreated after each wash with either 3 mg/m2 or 1 mg/m2 were subjected to gas chromatography analysis. This showed that the amounts of pyrethroid in the nets accumulated rapidly over the first few wash-retreatment cycles and then remained fairly stable over subsequent cycles. These nets gave consistently high bioassay mortalities throughout the experiment, while the mortality declined rapidly after several washes with the nets that were treated at 3 mg/m2 but not retreated. Experimental huts were used to compare the effectiveness of these 2 net retreatment regimes and nets which were not retreated. All nets caused high mortality rates amongst Anopheles females, but had negligible effects on culicines; either in killing them or in preventing feeding. Therefore use of a high 'loading' dose for initial treatment with lower 'maintenance' doses for retreatment may be preferable to ensure that net users promptly perceive the benefits of the insecticide against culicines.

Animals↗
PubMed2003

Absence of the kdr mutation in the molecular 'M' form suggests different pyrethroid resistance mechanisms in the malaria vector mosquito Anopheles gambiae s.s.

Field tests conducted on adult Anopheles mosquitoes using standard WHO procedures, diagnostic kits and test papers in south-western Nigeria showed pyrethroid (deltamethrin and permethrin) resistance in adult populations of Anopheles gambiae sensu stricto. The knock-down resistance (kdr) mutation involved in pyrethroid resistance was only found in the molecular S form of An. gambiae s.s. even in area where both molecular M and S forms occurred in sympatry. The absence of the kdr mutation in the M form suggests an additional pyrethroid resistance mechanism in An. gambiae s.s.

Animals↗
PubMed1995

Modulation in acetylcholinesterase of rat brain by pyrethroids in vivo and an in vitro kinetic study.

The modulation of acetylcholinesterase (AChE) of rat brain by two pyrethroids--permethrin (PM) and cypermethrin (CPM)--was studied both in vivo and in vitro. PM inhibited AChE activity in all regions of the rat brain (cerebral cortex, cerebellum, corpora striata, brain-stem, hippocampus, and hypothalamus) at 4, 8, and 12 h after gastric intubation, whereas CPM elevated the enzyme activity in vivo. Substrate-dependent enzyme kinetic studies have shown that PM and CPM behave as mixed-type inhibitors, as evidenced by alterations in both Michaelis-Menten constant (Km) and maximal velocity (Vmax) values. This indicates that both PM and CPM and substrate acetylcholine interact at hydrophobic subsites and may be able to bind simultaneously to the enzyme.

Acetylcholinesterase↗
PubMed2000

Scratching the itch: management of scabies in A&E.

Epidemics of scabies seem to occur in 20-25-year cycles. One of the resultant problems is that few A&E nurses practice through more than one epidemic and with each new outbreak of scabies, the latest generation of A&E nurses have to learn how to recognize and manage the disease. This article describes scabies, how to recognize it and the treatment options available. Although uncertainty remains, Permethrin is the first treatment of choice and should be used in the 5% cream form, not the 100% lotion. Crusted Norwegian scabies requires prompt and careful attention along with Specialist advice. The challenge for A&E staff is to recognize scabies, treat it appropriately and to help educate those most at risk.

Diagnosis, Differential↗
PubMed1998

Comparison of the cost-effectiveness of vaccines and insecticide impregnation of mosquito nets for the prevention of malaria.

The cost-effectiveness of two different methods of prevention of morbidity and mortality due to Plasmodium falciparum malaria, vaccination and impregnation of mosquito nets with permethrin, was compared. The analysis was performed with reference to the cohort of all children born in The Gambia in 1990 and protected for 5 years, using estimates of costs from studies in The Gambia. The vaccine was assumed to be given in three doses before the age of 6 months, through the Expanded Programme of Immunization, and to remain effective up to the age of 5 years. The bednets were assumed to be impregnated at 6-monthly intervals over the 5-year period. The expected number of deaths and attacks due to P. falciparum in the first 5 years of the 1990 cohort's lives were estimated from published literature. The numbers of deaths and attacks averted by the two strategies were then estimated by decision analysis, using the best estimates of effectiveness available in the literature. The vaccine strategy would have averted an estimated 743 deaths and 50,502 malaria attacks, whereas the net impregnation would have averted 1537 deaths and 69,415 attacks. The estimated cost per death averted was U.S. $252 for the vaccine and U.S. $711 for net impregnation. The estimated cost per P. falciparum attack averted was U.S. $3.71 for the vaccine and U.S. $15.75 for net impregnation. Sensitivity analysis, examining the effect of varying the vaccine cost or insecticide cost, the efficacy of the vaccine or net impregnation, and the percentage coverage of the population, confirmed the greater cost-effectiveness of the vaccine strategy for either of the outcomes examined under the conditions of the model. However, limitations on the absolute number of deaths and malaria attacks which can averted by currently available vaccines demonstrate that a vaccine of higher efficacy would be highly desirable.

Bedding and Linens↗
PubMed2000

Long term dynamics of dermanyssus gallinae in relation to mite control measures in aviary systems for layers.

1. The dynamics of the poultry red mite, Dermanyssus gallinae, in aviary systems for layers were studied in an empirical study in Sweden between 1994 and 1997. Fluctuations were monitored with mite traps at monthly intervals during 3 laying cycles at each of 2 commercial poultry farms. 2. When mites were first detected in the system it then took about 5 months for the populations to reach equilibrium levels around which they fluctuated. Within flocks when the population growth was unaffected by temporary control activities, it was demonstrated that the mite populations were significantly denser in summer than in winter. 3. Current control methods had limited effects as mite populations were only temporarily suppressed. One exception was the control achieved with permethrin impregnated plastic strips, which reduced the population at equilibrium level to approximately 22%, compared with the previous flock. 4. The distribution of mites was patchy horizontally, along the aviary system, at low burden wlhereas it became more evenly dispersed at equilibrium. 5. Significant differences in vertical mite distributions that correlated with the hybrids used and their rearing conditions were also observed. In flocks with brown hens, mites gathered at the lower tiers, whereas they were found at the highest tiers in association with white hens. As the hens are attacked mainly at night-time the most likely explanation is that the mites adjust their behavioural pattern to the birds' roosting behaviour.

Animal Husbandry↗
PubMed1997

Functional expression of Drosophila para sodium channels. Modulation by the membrane protein TipE and toxin pharmacology.

The Drosophila para sodium channel alpha subunit was expressed in Xenopus oocytes alone and in combination with tipE, a putative Drosophila sodium channel accessory subunit. Coexpression of tipE with para results in elevated levels of sodium currents and accelerated current decay. Para/TipE sodium channels have biophysical and pharmacological properties similar to those of native channels. However, the pharmacology of these channels differs from that of vertebrate sodium channels: (a) toxin II from Anemonia sulcata, which slows inactivation, binds to Para and some mammalian sodium channels with similar affinity (Kd congruent with 10 nM), but this toxin causes a 100-fold greater decrease in the rate of inactivation of Para/TipE than of mammalian channels; (b) Para sodium channels are >10-fold more sensitive to block by tetrodotoxin; and (c) modification by the pyrethroid insecticide permethrin is >100-fold more potent for Para than for rat brain type IIA sodium channels. Our results suggest that the selective toxicity of pyrethroid insecticides is due at least in part to the greater affinity of pyrethroids for insect sodium channels than for mammalian sodium channels.

Animals↗
PubMed2003

Review of common therapeutic options in the United States for the treatment of pediculosis capitis.

Numerous therapies are available in both over-the-counter and prescription formulations for the treatment of head lice infestation. We summarize treatment recommendations from published literature and from a recent meta-analysis from the Cochrane Database of Systematic Reviews that describe the efficacy, safety, and resistance patterns of monotherapies available in the United States. If treatment with pyrethrin or permethrin fails to eradicate the infestation, the treatment of choice is malathion. However, because of malathion's flammability, it should be a second-line therapy. Orally administered ivermectin has been reported to be efficacious, but it is not currently a US Food and Drug Administration-approved pediculicide. Alternative therapies are also discussed, in addition to indications for prophylaxis, resistance reporting, and the social impact of infestation.

Animals↗
PubMed1995

Seroepidemiology of infections due to spotted fever group rickettsiae and Ehrlichia species in military personnel exposed in areas of the United States where such infections are endemic.

A prospective, seroepidemiologic study of spotted fever group rickettsiae (SFGR) and Ehrlichia infections was done among 1194 US military personnel exposed in a heavily tick-infested area of Arkansas in 1990. Seroconversion (4-fold) and seroprevalence rates were determined by indirect immunofluorescent antibody assays. Seroconversions to SFGR occurred in 30 persons (2.5%), whereas seroconversion to Ehrlichia species occurred in 15 (1.3%). The majority of seroconverters did not report symptoms (22/30 [73%] of SFGR seroconverters; 10/15 [67%] of Ehrlichia species seroconverters). History of tick attachment was associated with seroconversion to SFGR (relative risk [RR] = 4.3, P < .001) and Ehrlichia species (RR = 3.6, P < .05). Use of permethrin-impregnated uniforms significantly decreased risk of infection (P < .01); use of bed nets increased risk by 4-fold. Tickborne infections represent a significant threat to military personnel training in areas in which these infections are endemic.

Adolescent↗
PubMed1990

Influence of insecticide treatment on German cockroach (Dictyoptera: Blattellidae) movement and dispersal within apartments.

Two similar studies were done to investigate effects of insecticide treatments on German cockroach, Blattella germanica (L.), movement and dispersal within individual units in multifamily housing. In the first study, Whitmire PT-565 Pyrethrum Insect Fogger (pyrethrins), Diazinon 4E (diazinon), Protector (permethrin), and Baygon 1.5 (propoxur) did not induce any significant changes in cockroach distribution, and rates of movement within apartments decreased. In the second study, populations treated with sublethal doses of pyrethrins and resmethrin settled to their original distribution 24 h after treatment. Results from both studies indicate that thorough insecticide applications do not significantly affect German cockroach population dispersal or movement patterns within apartments.

Animals↗
PubMed1991

Bioassay for detecting active site insensitivity in horn fly (Diptera: Muscidae) larvae.

A bioassay was used to detect active site insensitivity (knock-down resistance [kdr]) in pyrethroid resistant larvae of the horn fly, Haematobia irritans (L.). The larvae of the resistant population had KD50's 42.0-, 28.1- and 29.2-fold greater to permethrin, fenvalerate and lambda-cyhalothrin, respectively, compared with the susceptible population. In filter paper bioassays, resistant adult horn flies were 17 to 39.1 times less susceptible to the pyrethroids than susceptible adults at LC50. These results further document active site insensitivity as the major mechanism of pyrethroid resistance in the horn fly.

Animals↗
PubMed1996

Insecticide susceptibility of cat flea (Siphonaptera: Pulicidae) pupae.

Studies were conducted to investigate what protective nature the cocoon and nylon carpeting has against the performance of insecticides directed at cat flea, Ctenocephalides felis (Bouché), pupae developing in carpet. The following 5 combinations of life stages and substrates were used in these tests were: (1) larvae that pupated in carpet, (2) cocoons placed in carpet, (3) naked pupae placed in carpet, (4) cocoons placed on filter paper, and (5) naked pupae placed on filter paper. These studies evaluated the performance of chlorpyrifos, microencapsulated chlorpyrifos, propetamphos, permethrin, and linalool. When averaged over all insecticides, the mean controls of cocooned pupae placed in carpet and cocooned pupae placed on filter paper were 37.2 and 26.7%, respectively, whereas that of naked pupae placed in carpet was only 13.7%. Additional tests conducted using chlorpyrifos revealed that mortality was 23 and 42% higher, respectively, whenever pupae in cocoons and naked pupae were treated in glass dishes without filter paper. These studies demonstrate that the debri-coated cocoon is not a barrier to insecticide penetration, and that pupae appeared to be protected inside the carpet matrix. Additional studies demonstrated that control of pupae developing in carpet was maximized at lower application pressures. The mean control of pupae with chlorpyrifos at 0.7 kg/cm2 pressure was 77.2%, yet applications at 1.7 kg/cm2 resulted in only 23.3% control.

Animals↗
PubMed1997

Inheritance of CYP6D1-mediated pyrethroid resistance in house fly (Diptera: Muscidae).

The inheritance of cytochrome P450 monooxygenase-mediated (i.e., CYP6D1) resistance in the LPR strain of house fly, Musca domestica L., was investigated by comparing levels of monooxygenase-mediated permethrin resistance and CYP6D1 messenger RNA in 7 populations of house flies. Results indicate that monooxygenase-mediated resistance, and overexpression of CYP6D1 in the LPR strain are controlled by an incompletely recessive trans acting factor(s) on autosome 2 and a nearly completely dominant cis acting factor(s) on autosome 1. The polygenic nature of CYP6D1-mediated resistance and the relative dominance of the resistance factor(s) on autosome 1 suggests this type of resistance could develop relatively quickly.

Animals↗
PubMed1999

Independent selection of multiple mechanisms for pyrethroid resistance in Guatemalan Anopheles albimanus (Diptera: Culicidae).

Isofemale lines were established containing either, both, or neither of the elevated esterase and oxidase resistance mechanisms conferring pyrethroid resistance in a Guatemalan strain of Anopheles albimanus (Wiedemann). Plots of esterase and oxidase levels for individual mosquitoes from these single families correlated with data obtained using oxidase and esterase synergists in bioassays run in the bottle format. Mixed populations of pyrethroid-resistant A. albimanus adult females were selected using DDT, permethrin, or malathion; and the esterase and oxidase levels of the individual progeny were plotted. These data showed that the 3 classes of insecticide selected the 2 mechanisms differently. These results are discussed in terms of the problem of multiresistance surveillance in the field, especially concerning pyrethroid insecticides and the interaction of agricultural and public health insecticide application.

Animals↗
PubMed1991

Comparative sensitivity of four Anopheles (Diptera: Culicidae) to five repellents.

Five repellents were evaluated against Anopheles albimanus Wiedemann An. freeborni Aitken, An. gambiae Giles, and An. stephensi Liston, using a "free choice," dose-response testing procedure on rabbits. Overall, deet was the most effective repellent based on effective dosages (ED50's and ED95's), except against An. albimanus. An. albimanus was significantly more tolerant to deet compared with dimethyl phthalate or ethyl hexanediol. Permethrin was effective against all four anopheline species at the ED50 levels; however, the ED95 values were higher compared with the other repellents. There were significant differences in sensitivity of some of the four species to all the repellents tested, except dimethyl phthalate and indalone. The variability in the response of these anopheline species to repellents confirm that the extrapolation of repellent data from one anopheline species to another is unreliable and that comprehensive tests are needed for each species.

Animals↗