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Journal ArticleDOI

Monitoring of resistance to the pyrethroid cypermethrin in Brazilian Aedes aegypti (Diptera: Culicidae) populations collected between 2001 and 2003

TL;DR: Although this pyrethroid was recently started to be used in the country to control the dengue vector, a decrease in susceptibility was noted between both periods analyzed, particularly in the city of Rio de Janeiro, indicating that resistance is due at least in part to a target site alteration.
Abstract: Resistance to cypermethrin of different Aedes aegypti Brazilian populations, collected at two successive periods (2001 and 2002/2003), was monitored using the insecticide-coated bottles bioassay. Slight modifications were included in the method to discriminate between mortality and the knock down effect. Although this pyrethroid was recently started to be used in the country to control the dengue vector, a decrease in susceptibility was noted between both periods analyzed, particularly in the city of Rio de Janeiro. The results indicate that resistance is due at least in part to a target site alteration.

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Citations
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Journal ArticleDOI
TL;DR: Annotation of the recently determined genome sequence of the major dengue vector, Aedes aegypti, reveals an abundance of detoxification genes, and an array containing unique oligonucleotide probes for these genes was constructed and compared their expression level in insecticide resistant and susceptible strains.

319 citations

Journal ArticleDOI
TL;DR: The status of pyrethroid resistance in A. aegypti and A. albopictus is reviewed, mechanisms of resistance, fitness costs associated with resistance alleles and suggestions for future research are presented.

247 citations

Journal ArticleDOI
TL;DR: Joint genomic, biochemical and microarray studies will help unravel the classification of this complex gene family, which appears to be rapidly evolving and each insect species has a unique complement of detoxification genes with only a few orthologues across species.
Abstract: The use of chemical insecticides continues to play a major role in the control of disease vector populations, which is leading to the global dissemination of insecticide resistance. A greater capacity to detoxify insecticides, due to an increase in the expression or activity of three major enzyme families, also known as metabolic resistance, is one major resistance mechanisms. The esterase family of enzymes hydrolyse ester bonds, which are present in a wide range of insecticides; therefore, these enzymes may be involved in resistance to the main chemicals employed in control programs. Historically, insecticide resistance has driven research on insect esterases and schemes for their classification. Currently, several different nomenclatures are used to describe the esterases of distinct species and a universal standard classification does not exist. The esterase gene family appears to be rapidly evolving and each insect species has a unique complement of detoxification genes with only a few orthologues across species. The examples listed in this review cover different aspects of their biochemical nature. However, they do not appear to contribute to reliably distinguish among the different resistance mechanisms. Presently, the phylogenetic criterion appears to be the best one for esterase classification. Joint genomic, biochemical and microarray studies will help unravel the classification of this complex gene family.

204 citations

Journal ArticleDOI
TL;DR: Two A. aegypti populations from Ceará are under strong selection pressure by temephos, compromising the field effectiveness of this organophosphate, and resistance to cypermethrin is shown in two of the three populations studied.
Abstract: Organophosphates and pyrethroids are used widely in Brazil to control Aedes aegypti, the main vector of dengue viruses, under the auspices of the National Programme for Dengue Control. Resistance to these insecticides is widespread throughout Brazil. In Ceara the vector is present in 98% of districts and resistance to temephos has been reported previously. Here we measure resistance to temephos and the pyrethroid cypermethrin in three populations from Ceara and use biochemical and molecular assays to characterise resistance mechanisms. Resistance to temephos varied widely across the three studied populations, with resistance ratios (RR95) of 7.2, 30 and 192.7 in Juazeiro do Norte, Barbalha and Crato respectively. The high levels of resistance detected in Barbalha and Crato (RR95 ≥ 30) imply a reduction of temephos efficacy, and indeed in simulated field tests reduced effectiveness was observed for the Barbalha population. Two populations (Crato and Barbalha) were also resistant to cypermethrin, whilst Juazeiro do Norte showed only an altered susceptibility. The Ile1011Met kdr mutation was detected in all three populations and Val1016Ile in Crato and Juazeiro do Norte. 1011Met was significantly associated with resistance to cypermethrin in the Crato population. Biochemical tests showed that only the activity of esterases and GSTs, among the tested detoxification enzymes, was altered in these populations when compared with the Rockefeller strain. Our results demonstrate that two A. aegypti populations from Ceara are under strong selection pressure by temephos, compromising the field effectiveness of this organophosphate. Our results also provide evidence that the process of reducing resistance to this larvicide in the field is difficult and slow and may require more than seven years for reversal. In addition, we show resistance to cypermethrin in two of the three populations studied, and for the first time the presence of the allele 1016Ile in mosquito populations from northeastern Brazil. A significant association between 1011M et and resistance was observed in one of the populations. Target-site mechanisms seem not to be implicated in temephos resistance, reinforcing the idea that for the studied populations, detoxification enzymes most likely play a major role in the resistance to this insecticide.

204 citations

01 Mar 2010
TL;DR: The lack of publicly accessible standardized data sets dcoumenting levels of insecticide resistance in many dengue endemic countries, and the absence of studies on the operational impact of resistance, preculdes a comprehensive analysis of the current global threat that insecticides resistance poses to d Dengue control.
Abstract: Background: Most national dengue control programmes rely extensively on insecticides to control the mosquito vectors of this disease. Objectives: The objective of this review is to describe current knowledge of the extent of insecticide resistance in dengue vectors and the potential impact of this resistance on control activities. Methods: We searched Web of Science and PubMed for studies that included data on resistance to the four major classes of insecticides: organochlorines, carbamates, organophosphates and pyrethroids, in the dengue vectors Aedes aegypti and Aedes albopictus. Insecticide bioassy data were extracted from the published literature and the methods used to obtain, analyse and interpret this data were critically evaluated. Emphasis was placed on the two insecticide classes most widely used in dengue control, organophosphates and pyrethroids. The use of biochemical and molecular tools for resistance monitoring was also reviewed. Results: 66 studies met our inclusion criteria and were uploaded on to a public databse (IRBase). There is a stong geographical bias in published studies with nearly half originating from three countries (Thailand, India and Brazil). Bioassay data demonstrates that resistance to the organophosphate temephos and to pyrethroids is widespread in Ae. aegypti and resistance has also been reported in Ae. albopictus. Assessing the impact of insecticide resistance on vector control is complicated by variations in the methodology used to measure and report resistance, and by the lack of studies into the epidemiological consequences of insecticicde resistance. Conclusions: The lack of publicly accessible standardized data sets dcoumenting levels of insecticide resistance in many dengue endemic countries, and the absence of studies on the operational impact of resistance, preculdes a comprehensive analysis of the current global threat that insecticide resistance poses to dengue control. However, several countries with active resistance monitoring programmes have shown that insecticide resistance is reducing our ability to control dengue vectors. This situation is likely to worsen unless effective strategies are rapidly implemented to mitigate these effects.

197 citations

References
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Journal Article
TL;DR: The authors discuss such dosages in respect of dieldrin and DDT, and put forward newly-established tentative discriminating dosages for organophosphorus and carbamate insecticides, which await field confirmation.
Abstract: Insecticide resistance is an inherent characteristic dependent on relatively simple genetic mechanisms. This seems to be especially true of dieldrin resistance in anopheline mosquitos, though less obvious in DDT resistance among these species; little is known as yet about the inheritance of organophosphate and carbamate resistance as it occurs in Anopheles albimanus. The speed of selection of resistance depends on the original frequency of the gene or genes involved, the nature of the resistance imparted, and the selection pressure of the insecticide. This in turn depends on the inherent toxicity of the chemical, the efficiency with which it is applied, the proportion of the mosquito population coming under its influence, and the behaviour of the mosquito. In the past, too much reliance has been placed on the determination of the LD50 in assessing the presence or absence of insecticide resistance. Quite high incidences of resistant individuals can result in such small changes in the LD50 that resistance may be overlooked. The use of single discriminating dosages is advocated, based on concentrations of insecticides that normally kill all susceptible individuals. The authors discuss such dosages in respect of dieldrin and DDT, and put forward newly-established tentative discriminating dosages for organophosphorus and carbamate insecticides, which await field confirmation. From a practical standpoint, an insecticide should not be abandoned or replaced by another as soon as resistance is confirmed. This may not be necessary where the degree of resistance is not high and the vector is not highly efficient. Certain procedures are proposed in order to assess the epidemiological and entomological implications of resistance before the insecticide concerned is abandoned.

88 citations


"Monitoring of resistance to the pyr..." refers background in this paper

  • ...Intermediate values are indicative of an incipient altered susceptible status and point to the need of surveillance of the population (Davidson & Zahar 1973)....

    [...]

Journal ArticleDOI

87 citations


"Monitoring of resistance to the pyr..." refers background in this paper

  • ...Sodium channels are also the target site for organochlorines, an insecticide class that has not been used in the Public Health at Brazil since the reintroduction of Ae. aegypti in 1967 (Franco 1976)....

    [...]

Journal ArticleDOI
TL;DR: It is concluded that linkage between pyrethroid and batrachotoxin binding sites is altered in the pyrethoid-resistant fly strains, probably due to a drastically decreased affinity of the Na{sup +} channel for pyrethroids.
Abstract: Resistance to insecticides is a major problem in agriculture. ({sup 3}H)Saxitoxin binding experiments have shown that pyrethroid-sensitive and pyrethroid-resistant flies have the same amount of Na{sup +} channel protein in their brain membranes. Also, although flies are resistant to pyrethroids, they remain as sensitive to batrachotoxin, which is another type of Na{sup +} channel activators, as pyrethroid-sensitive flies. Pyrethroid binding sites have been characterized by use of the properties of pyrethroids to increase the specific ({sup 3}H)batrachotoxinin A 20{alpha}-benzoate binding component. K{sub 0.5} values for association of pyrethroids at the Na{sup +} channel of pyrethroid-sensitive flies are in the range of 0.15-0.25 {mu}M. Conversely, pyrethroids do not produce a significant increase of ({sup 3}H)batrachotoxinin A 20{alpha}-benzoate binding in pyrethroid-resistant flies even at high concentrations of the insecticide. It is concluded that linkage between pyrethroid and batrachotoxin binding sites is altered in the pyrethroid-resistant fly strains. This alteration is probably due to a drastically decreased affinity of the Na{sup +} channel for pyrethroids.

85 citations


"Monitoring of resistance to the pyr..." refers background in this paper

  • ...Resistant individuals that have a kdr mutation exhibit the knock down effect but can recover from pyrethroid dosages that are lethal to susceptible insects (Milani 1954, Pauron et al. 1989)....

    [...]

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