Last data update: Jun 17, 2024. (Total: 47034 publications since 2009)
Records 1-7 (of 7 Records) |
Query Trace: Brogdon WG [original query] |
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An Operational Framework for Insecticide Resistance Management Planning
Chanda E , Thomsen EK , Musapa M , Kamuliwo M , Brogdon WG , Norris DE , Masaninga F , Wirtz R , Sikaala CH , Muleba M , Craig A , Govere JM , Ranson H , Hemingway J , Seyoum A , Macdonald MB , Coleman M . Emerg Infect Dis 2016 22 (5) 773-9 Arthropod vectors transmit organisms that cause many emerging and reemerging diseases, and their control is reliant mainly on the use of chemical insecticides. Only a few classes of insecticides are available for public health use, and the increased spread of insecticide resistance is a major threat to sustainable disease control. The primary strategy for mitigating the detrimental effects of insecticide resistance is the development of an insecticide resistance management plan. However, few examples exist to show how to implement such plans programmatically. We describe the formulation and implementation of a resistance management plan for mosquito vectors of human disease in Zambia. We also discuss challenges, steps taken to address the challenges, and directions for the future. |
Determination of insecticidal effect (LC50 and LC90) of organic fatty acids mixture (C8910+Silicone) against Aedes aegypti and Aedes albopictus (Diptera: Culicidae)
Dunford JC , Falconer A , Leite LN , Wirtz RA , Brogdon WG . J Med Entomol 2015 53 (3) 699-702 Emerging and re-emerging vector-borne diseases such as chikungunya and dengue and associated Aedes vectors are expanding their historical ranges; thus, there is a need for the development of novel insecticides for use in vector control programs. The mosquito toxicity of a novel insecticide and repellent consisting of medium-chain carbon fatty acids (C8910) was examined. Determination of LC50 and LC90 was made against colony-reared Aedes aegypti (L.) and Aedes albopictus (Skuse) using probit analysis on mortality data generated by Centers for Disease Control and Prevention bottle bioassays. Six different concentrations of C8910 + silicone oil yielded an LC50 of 160.3 microg a.i/bottle (147.6-182.7) and LC90 of 282.8 (233.2-394.2) in Ae. aegypti; five concentrations yielded an LC50 of 125.4 (116.1-137.6) and LC90 of 192.5 (165.0-278.9) in Ae. albopictus. Further development of C8910 and similar compounds could provide vector control specialists novel insecticides for controlling insect disease vectors. |
When a discriminating dose assay is not enough: measuring the intensity of insecticide resistance in malaria vectors
Bagi J , Grisales N , Corkill R , Morgan JC , N'Fale S , Brogdon WG , Ranson H . Malar J 2015 14 (1) 210 BACKGROUND: Guidelines from the World Health Organization for monitoring insecticide resistance in disease vectors recommend exposing insects to a predetermined discriminating dose of insecticide and recording the percentage mortality in the population. This standardized methodology has been widely adopted for malaria vectors and has provided valuable data on the spread and prevalence of resistance. However, understanding the potential impact of this resistance on malaria control requires a more quantitative measure of the strength or intensity of this resistance. METHODS: Bioassays were adapted to quantify the level of resistance to permethrin in laboratory colonies and field populations of Anopheles gambiae sensu lato. WHO susceptibility tube assays were used to produce data on mortality versus exposure time and CDC bottle bioassays were used to generate dose response data sets. A modified version of the CDC bottle bioassay, known as the Resistance Intensity Rapid Diagnostic Test (I-RDT), was also used to measure the knockdown and mortality after exposure to different multipliers of the diagnostic dose. Finally cone bioassays were used to assess mortality after exposure to insecticide treated nets. RESULTS: The time response assays were simple to perform but not suitable for highly resistant populations. After initial problems with stability of insecticide and bottle washing were resolved, the CDC bottle bioassay provided a reproducible, quantitative measure of resistance but there were challenges performing this under field conditions. The I-RDT was simple to perform and interpret although the end point selected (immediate knockdown versus 24 h mortality) could dramatically affect the interpretation of the data. The utility of the cone bioassays was dependent on net type and thus appropriate controls are needed to interpret the operational significance of these data sets. CONCLUSIONS: Incorporating quantitative measures of resistance strength, and utilizing bioassays with field doses of insecticides, will help interpret the possible impact of resistance on vector control activities. Each method tested had different benefits and challenges and agreement on a common methodology would be beneficial so that data are generated in a standardized format. This type of quantitative data are an important prerequisite to linking resistance strength to epidemiological outcomes. |
Pyrethroid resistance in Anopheles gambiae s.s. and Anopheles arabiensis in western Kenya: phenotypic, metabolic and target site characterizations of three populations
Ochomo E , Bayoh MN , Brogdon WG , Gimnig JE , Ouma C , Vulule JM , Walker ED . Med Vet Entomol 2012 27 (2) 156-64 ![]() Field and laboratory investigations revealed phenotypic, target site and metabolic resistance to permethrin in an Anopheles gambiae s.s. (Diptera: Culicidae) population in Bungoma District, a region in western Kenya in which malaria is endemic and rates of ownership of insecticide-treated bednets are high. The sensitivity of individual An. gambiae s.l. females as indicated in assays using World Health Organization (WHO) test kits demonstrated reduced mortality in response to permethrin, deltamethrin and bendiocarb. Estimated time to knock-down of 50% (KDT(50) ) of the test population in Centers for Disease Control (CDC) bottle bioassays was significantly lengthened for the three insecticides compared with that in a susceptible control strain. Anopheles arabiensis from all three sites showed higher mortality to all three insecticides in the WHO susceptibility assays compared with the CDC bottle assays, in which they showed less sensitivity and longer KDT(50) than the reference strain for permethrin and deltamethrin. Microplate assays revealed elevated activity of beta-esterases and oxidases, but not glutathione-S-transferase, in An. gambiae s.s. survivors exposed to permethrin in bottle bioassays compared with knocked down and unexposed individuals. No An. arabiensis showed elevated enzyme activity. The 1014S kdr allele was fixed in the Bungoma An. gambiae s.s. population and absent from An. arabiensis, whereas the 1014F kdr allele was absent from all samples of both species. Insecticide resistance could compromise vector control in Bungoma and could spread to other areas as coverage with longlasting insecticide-treated bednets increases. |
Characterization of insecticide resistance in Trinidadian strains of Aedes aegypti mosquitoes
Polson KA , Brogdon WG , Rawlins SC , Chadee DD . Acta Trop 2011 117 (1) 31-8 Bioassays and biochemical assays were conducted on eight Trinidadian strains of Aedes aegypti larvae to determine the involvement of biochemical mechanisms in resistance to insecticides. Larval strains were assayed to dichlorodiphenyltrichloroethane (DDT), bendiocarb, temephos and permethrin, using the Centers for Disease Control and Prevention (CDC) time-mortality bioassay method. A Resistance Threshold (RT) was calculated for each insecticide in relation to the CAREC reference susceptible Ae. aegypti strain and larval strains with <80% mortality were considered to be resistant. Biochemical assays were performed to determine the activities of nonspecific esterases (alpha- and beta-), PNPA-esterases, mixed function oxidases (MFO), glutathione-S-transferases (GST) and acetylcholinesterase (AChE) enzymes which are involved in insecticide resistance in mosquitoes. Enzyme profiles of each strain were compared with those of the CAREC reference susceptible strain by Kruskal-Wallis and Dunn's multiple comparison tests (p<0.05). The CAREC 99th percentile was calculated for each enzyme and the percentage of individuals with enzyme activities above that of the CAREC 99th percentile was calculated. Activities were classified as unaltered (<50%), incipiently altered (15-50%) or altered (>50%) for each strain. The established RTs for permethrin and bendiocarb were 30 and 75 min, respectively; and 120 min for DDT and temephos. All strains were resistant to DDT (1.00-40.25% mortality) and temephos (11.50-74.50% mortality) while six strains were resistant to bendiocarb (51.50-78.50% mortality) and five to permethrin (6.50-42.50% mortality). Biochemical assays revealed that the median activity levels for all enzymes varied significantly (p<0.05). The Curepe strain had incipiently altered levels of alpha-esterase while the other seven strains had altered activity with five of them registering 100%. The St Clair strain showed altered activity levels of beta-esterase while three strains had incipiently altered levels. The majority of strains had altered activity of MFO enzymes but only the St Clair strain showed altered activity of GST. PNPA-esterases activity was unaltered in all strains and only the Haleland Park strain showed altered remaining AChE activity in the presence of propoxur. Elevated levels of enzymes (incipiently altered or altered), except in the case of PNPA-esterases, show that biochemical resistance may play an important role in the manifestation of insecticide resistance in Trinidadian populations of Ae. aegypti. It is therefore important for insecticide resistance surveillance to be ongoing as the detection of resistance before it spreads throughout an entire population makes it possible for early intervention. |
Pyrethroid and organophosphates resistance in Anopheles (N.) nuneztovari Gabaldon populations from malaria endemic areas in Colombia
Fonseca-Gonzalez I , Cardenas R , Quinones ML , McAllister J , Brogdon WG . Parasitol Res 2009 105 (5) 1399-409 Field populations of Colombian malaria vector Anopheles (N.) nuneztovari were studied using World Health Organization (WHO) and Center for Disease Control and Prevention (CDC) bioassay techniques and through the use of biochemical microplate-based assays for resistance enzymes. Insecticides evaluated included the pyrethroids lambda-cyhalothrin and deltamethrin, organophosphates malathion and fenitrothion, and the organochlorine dichlorodiphenyltrichloroethane (DDT). Study sites selected were based upon malaria incidence, vector presence, and control activities in Colombia. Early stage selection for reduced susceptibility was observed in the bioassays for some locations. Data from the WHO and CDC bioassay methods were broadly consistent, with some differences noted. Evidence is presented for low-level initial selection of some resistance mechanisms such as mixed-function oxidases and modified acetylcholinesterase. Data from the site Encharcazon implies that selection for DDT-pyrethroid cross-resistance has occurred, though not likely at a level that currently threatens vector control by either class of insecticides, and further implies that knockdown resistance (kdr) may be present in those populations. Further studies using synergists and development of a kdr-specific assay for A. nuneztovari thus become priorities. The resistance levels to lambda-cyhalothrin and deltamethrin found in the Encharcazon population are of concern since these two insecticides are currently used for both indoor spraying and treated nets. In addition, the resistance to fenitrothion, the indoor spray insecticide mostly used for this species due to their exophilic behavior, found in the El Zulia population, makes urgent to find alternatives for chemical control in these areas. These data provide the initial baselines for insecticide susceptibility profiles for A. nuneztovari in Colombia and the first report of insecticide resistance in this vector. |
Adaptation and evaluation of the bottle assay for monitoring insecticide resistance in disease vector mosquitoes in the Peruvian Amazon
Zamora Perea E , Balta Leon R , Palomino Salcedo M , Brogdon WG , Devine GJ . Malar J 2009 8 208 BACKGROUND: The purpose of this study was to establish whether the "bottle assay", a tool for monitoring insecticide resistance in mosquitoes, can complement and augment the capabilities of the established WHO assay, particularly in resource-poor, logistically challenging environments. METHODS: Laboratory reared Aedes aegypti and field collected Anopheles darlingi and Anopheles albimanus were used to assess the suitability of locally sourced solvents and formulated insecticides for use with the bottle assay. Using these adapted protocols, the ability of the bottle assay and the WHO assay to discriminate between deltamethrin-resistant Anopheles albimanus populations was compared. The diagnostic dose of deltamethrin that would identify resistance in currently susceptible populations of An. darlingi and Ae. aegypti was defined. The robustness of the bottle assay during a surveillance exercise in the Amazon was assessed. RESULTS: The bottle assay (using technical or formulated material) and the WHO assay were equally able to differentiate deltamethrin-resistant and susceptible An. albimanus populations. A diagnostic dose of 10 microg a.i./bottle was identified as the most sensitive discriminating dose for characterizing resistance in An. darlingi and Ae. aegypti. Treated bottles, prepared using locally sourced solvents and insecticide formulations, can be stored for > 14 days and used three times. Bottles can be stored and transported under local conditions and field-assays can be completed in a single evening. CONCLUSION: The flexible and portable nature of the bottle assay and the ready availability of its components make it a potentially robust and useful tool for monitoring insecticide resistance and efficacy in remote areas that require minimal cost tools. |
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