Insecticide resistance in two Aedes aegypti (Diptera: Culicidae) strains from Costa Rica.

Dengue (family Flaviridae, genus Flavivirus, DENV) and dengue hemorrhagic fever (DHF) are presently important public health problems in Costa Rica. The primary strategy for disease control is based on reducing population densities of the main mosquito vector Aedes aegypti (L.) (Diptera: Culicidae). This is heavily dependent on use of chemical insecticides, thus the development of resistance is a frequent threat to control program effectiveness. The objective of this study was to determine the levels of insecticide resistance and the metabolic resistance mechanisms involved in two Ae. aegypti strains collected from two provinces (Puntarenas and Limon) in Costa Rica. Bioassays with larvae were performed according to World Health Organization guidelines and resistance in adults was measured through standard bottle assays. The activities of beta-esterases, cytochrome P450 monooxygenases, and glutathione S-transferases (GST), were assayed through synergists and biochemical tests, wherein the threshold criteria for each enzyme was established using the susceptible Rockefeller strain. The results showed higher resistance levels to the organophosphate (OP) temephos and the pyrethroid deltamethrin in larvae. The efficacy of commercial formulations of temephos in controlling Ae. aegypti populations was 100% mortality up to 11 and 12 d posttreatment with daily water replacements in test containers. Temephos and deltamethrin resistance in larvae were associated with high esterase activity, but not to cytochrome P450 monooxygenase or GST activities. Adult mosquitoes were resistant to deltamethrin, and susceptible to bendiocarb, chlorpyrifos, and cypermethrin. Because temephos and deltamethrin resistance are emerging at the studied sites, alternative insecticides should be considered. The insecticides chlorpyrifos and cypermethrin could be good candidates to use as alternatives for Ae. aegypti control.

An investigation of lumbar spine magnetic resonance referrals in two Irish university teaching centres: Radiology clinical judgement versus iRefer guideline compliance.

INTRODUCTION: With the annual increase in medical imaging demand, the appropriateness of the lumbar spine magnetic resonance imaging LSMRI referrals is worldwide gaining attention. This study aims to determine the appropriateness of LSMRI referrals and compare radiology clinical decisions to iRefer compliance based solely on referral text content. METHODS: Referral text was extracted from 1021 LSMRI referrals. Two review panels were recruited: three expert radiologists and three MRI radiographers. Radiologists classified cases as indicated or not indicated for scanning based on their clinical judgement. The radiographers classified based solely on iRefer guidelines. Majority voting for each case was applied to both review panels and reviewer agreement was tested using Kappa analysis. Logistic regression models were developed to identify medical disciplines associated with high rates of indicated referrals. RESULTS: 21.7% and 11.9% of the cases were found not indicated for MRI for radiologists and radiographers, respectively. Radiology review identified 18% of the GPs referrals as not indicated and 17% in the radiographers' review. Panel agreement was fair: Kappa values of 0.23 and0.26 for the radiologists and radiographers respectively. Neurosurgery was associated with the highest rate of indicated referrals across both review panels: oncology referrals raised the highest number of open comments. CONCLUSION: The study identified a lower number of not indicated referrals compared to previous research. Findings indicate the importance of both guidelines compliance and clinical judgement to optimise practice. IMPLICATIONS FOR PRACTICE: Findings in this study found that even when strict instructions were given to the MR radiographers to vet referrals using the iRefer guidelines, ambiguity within the guidelines resulted in variations in decision-making. This suggests that detailed protocols are required to support radiographers in the vetting process to ensure a standardised approach.

Temephos resistance and esterase activity in the mosquito Aedes aegypti in Havana, Cuba increased dramatically between 2006 and 2008.

Aedes aegypti (L.) (Diptera: Culicidae) control programmes in Cuba rely on the application of the organophosphate temephos for larval control. Hence, the monitoring of resistance to this insecticide is an essential component of such programmes. Here, 15 field populations from different municipalities of Havana City were assayed for resistance to temephos. High levels of resistance were detected in all strains and resistance ratios were highly correlated with esterase activity (P = 0.00001). Populations from three municipalities were tested in both 2006 and 2008; resistance and esterase activities both significantly increased during this 2-year period. Synergist studies demonstrated that neither glutathione transferases nor monooxygenases were associated with the increase in resistance to temephos in this period. The duration of the efficacy of commercial formulations of temephos in controlling Ae. aegypti populations in Havana City was reduced by the high level of temephos resistance observed; hence these data are of clear operational significance for the dengue control programme in Cuba. New integrated strategies to avoid further increases in temephos resistance in Cuba are necessary.

Multiple insecticide resistance in Aedes aegypti (Diptera: Culicidae) from Boyeros municipality, Cuba and associated mechanisms.

In this study, insecticide resistance and the mechanisms responsible were characterized in Ae. aegypti of Boyeros municipality from Havana, Cuba. Boyeros represents a high epidemiological risk because it is located near the Havana International Airport, it is highly urbanized, and it has a large influx of people from endemic countries so that it qualifies as a sentinel site for surveillance. The larvae collected from five areas of this municipality showed resistance to temephos associated with metabolic enzymes. The adult mosquitoes displayed a deltamethrin resistance and less distinctly to other pyrethroids associated with a high frequency of sodium channel gene mutations (F1534C and V1016I), detected for the first time in a field population from Cuba. The presence in the field populations of two insecticide resistance mechanisms represents a limiting factor in the success of the control operations of this vector, so other strategies should be considered to preserve the effectiveness of the insecticides available in public health for vector control in Cuba.

Insecticide resistance studies on Blattella germanica (Dictyoptera:Blattellidae) from Cuba.

We studied the levels of resistance to seven insecticides: malathion, chlorpyrifos, pirimiphos-methyl, propoxur, cypermethrin, deltamethrin, and lambda-cyhalothrin in nine strains of Blattella germanica (Linnaeus, 1717) collected from sites in Santiago de Cuba and Havana City. The strains from Santiago de Cuba, generally had high levels of resistance to malathion, cypermethrin, deltamethrin, and lambda-cyhalothrin, but only low levels of resistance to pirimiphos-methyl, chlorpyrifos, and propoxur. In the strains from Havana City we found a moderate resistance to the organophosphate insecticides, resistance to the pyrethroids (except for three strains that showed susceptibility to lambda-cyhalothrin), and susceptibility to the carbamate insecticide (propoxur).

Cross-resistance to pyrethroid and organophosphorus insecticides in the southern house mosquito (Diptera:Culicidae) from Cuba.

A sample of the southern house mosquito, Culex pipiens quinquefasciatus Say, from Cuba was subjected to lambda-cyhalothrin selection to evaluate the usefulness of this pyrethroid insecticide for mosquito control. High resistance developed after 6 generations of selection. Little or no cross-resistance was observed to other pyrethroids (deltamethrin and cypermethrin), to a carbamate (propoxur) and to some organophosphates (chlorpyrifos and pirimiphos-methyl), but high cross-resistance was found to malathion (organophosphate). Possible resistance mechanisms responsible for this phenomenon are discussed.

Detection of insecticide resistance in Aedes aegypti (Diptera: Culicidae) from Cuba and Venezuela.

Four strains of Aedes aegypti (L.), one from Cuba and three from Venezuela, were bioassayed for susceptibility to eight insecticides, including the organophosphates, temephos, malathion, fenthion, pirimiphos methyl, and chlorpyrifos, and the pyrethroids, deltamethrin, lambda cyhalothrin and cypermethrin, S, S, S,-tributyl phosphorotrithioate and piperonyl butoxide were used as synergists to assess the involvement of esterases and monooxygenases in organophosphate resistance. Venezuelan strains had low levels of resistance to fenthion and malathion, and moderate to high resistance to temephos, pyrimphos methyl, and chlorpiriphos. All strains were susceptible to the pyrethroids, except the Cuban strain, which had moderate levels of resistance to cypermethrin. Organophosphate resistance in Ae. aegypti is a serious threat to control operations. Integrated strategies for Ae. aegypti control to prevent or delay pyrethroid resistance in Venezuela and Cuba are discussed.

Determination of Ace.1 Genotypes in Single Mosquitoes: Toward an Ecumenical Biochemical Test

The occurrence of two acetylcholinesterases, AChE1 and AChE2, in the mosquito Culex pipiens has been recently documented. Resistance to organophosphates and carbamates due to target insensitivity is the result of a qualitative change of only AChE1, encoded by the Ace.1 gene. Because AChE1 and AChE2 differ in their sensitivity to inhibitors, Ace.1 genotypes can be misclassified by previous tests. We describe a new rapid microplate test that allows unambiguous identification of Ace.1 genotypes. This test involves comparing AChE activities in the absence of insecticide and in the presence of two propoxur concentrations: a low concentration that inhibits only the sensitive AChE1 and a higher concentration that inhibits also AChE2 but not the insensitive AChE1 responsible of insecticide resistance. This comparison allows the identification of the three Ace.1 genotypes: resistant (Ace.1RR), susceptible (Ace.1SS) homozygotes, and heterozygotes (Ace.1RS). The similarity of propoxur sensitivity of modified AChE1s found in various resistant strains from the United States, Europe, and Africa indicates that this test is probably suitable for all the Ace.1 alleles described so far in C. pipiens.

Detoxifying esterases in Culex pipiens quinquefasciatus from the Caribbean countries.

Several over-produced esterases confer resistance to organophosphorus insecticides in the Culex pipiens complex. We describe their distribution in islands and countries of the Caribbean region based on new collections and previous studies, and discuss the need to: 1) undertake DNA studies to correctly identify the esterase B alleles that are amplified in different regions, and 2) investigate the variability among gene copies within each amplification system in order to fully understand their origin and their evolution through time.

[Study of two goitrous endemic areas in Niger: Belley-Koira and Tiguey-Tallawal]. / Etude de deux foyers d'endémie goitreuse au Niger: Belley-Koira et Tiguey-Tallawal.

The present work reports the clinical and laboratory findings in two endemic areas in Niger: Tiguey-Tallawal and Belley-Koira. The goitrous subjects (n = 293), mainly children and adolescents, have clinical evidence of euthyroidism but with biological criteria of hypothyroidism in 25% of cases as shown by the decrease of the total serum T4 and the increase of serum TSH. Iodine deficiency intake evaluated by the determination of urinary iodine in single urine specimens is the permissive and main factor for goiter endemicity = 14 +/- 7 micrograms/l in Belley-Koira (n = 99), 26 +/- 23 micrograms/l in Tiguey (n = 155) and 25 +/- 19 micrograms/l in Tallawal (n = 95). The single intramuscular injection of iodized oil (240 mg of iodine) constitutes an extremely effective way of correcting iodine deficiency: decrease of volume or disappearance of goiter among 291 subjects out of 362 i.e. 80%, twelve months after the injection. The diffuse goiter, more numerous (n = 270) than nodular goiter (n = 92) are corrected with more efficiency (85% versus 50%). We also noted that non goitrous subjects living in these two endemic areas show a severe iodine deficiency (urinary iodine: 33 +/- 18 mu/l; n = 70 = 76) while those living in non endemic areas present a moderate or a low iodine deficiency, respectively in Niamey (urinary iodine: 48 +/- 36 micrograms/l; n = 200) and in Tamou (urinary iodine: 80 +/- 29 micrograms/l; n = 69). Severe, moderate and low iodine deficiency seem to be correlated with nutritional habits: mil in endemic areas, mil and meat in Niamey and mil, meat, milk and fish in Tamou. The nutriments eaten in Niger have a low iodine level except ewe milk: salt (270 to 7100 micrograms/kg), woman milk (40 +/- 21 micrograms/l) cow milk (22 micrograms/l) goat milk (50 micrograms/l), ewe milk (294 micrograms/l). Salt consumption, evaluated by the determination of urinary chloride, is adequate. Prophylaxis by iodinated salt should be well accepted. No other factors than iodine deficiency in the etiology of endemic goiter, mainly nutritional (goitrogens or protein-calorie malnutrition) can be evoked to explain clinical and biochemical discrepancies between subjects living in the same morbid territory.

Epidemiology and prophylaxis of endemic goitre in the Bwa village of Sirao (Mali).

A study was conducted in Mali, in some villages exposed to iodine deficiency disorders (IDD). To treat and, above all, prevent endemic goitre, Lipiodol UF was dispensed in two ways: by intra-muscular injection (475 mg I) or by oral administration (48 mg I to 240 mg I). In two cases, hormone levels regained normal values and thyroid hypertrophies regressed significantly. Nevertheless, the impact of the treatment on the size of the goitres seems to be in favour of injections; which is probably due to the fact that in the village which received Lipiodol UF per os, many goitres were nodular.

A mutation in the voltage-gated sodium channel gene associated with pyrethroid resistance in Latin American Aedes aegypti.

Pyrethroids are commonly used as mosquito adulticides and evolution of resistance to these compounds is a major threat to public health. 'Knockdown resistance' to pyrethroids (kdr) is frequently caused by nonsynonymous mutations in the voltage-gated sodium channel transmembrane protein (para) that reduce pyrethroid binding. Early detection of kdr is critical to the development of resistance management strategies in mosquitoes including Aedes aegypti, the most prevalent vector of dengue and yellow fever viruses. Brengues et al. described seven novel mutations in hydrophobic segment 6 of domain II of para in Ae. aegypti. Assays on larvae from strains bearing these mutations indicated reduced nerve sensitivity to permethrin inhibition. Two of these occurred in codons Iso1011 and Val1016 in exons 20 and 21 respectively. A transition in the third position of Iso1011 encoded a Met1011 replacement and a transversion in the second position of Val1016 encoded a Gly1016 replacement. We have screened this same region in 1318 mosquitoes in 32 additional strains; 30 from throughout Latin America. While the Gly1016 allele was never detected in Latin America, we found two new mutations in these same codons. A transition in the first position of codon 1011 encodes a Val replacement while a transition in the first position of codon 1016 encodes an Iso replacement. We developed PCR assays for these four mutations that can be read either on an agarose gel or as a melting curve. Selection experiments, one with deltamethrin on a field strain from Santiago de Cuba and another with permethrin on a strain from Isla Mujeres, Mexico rapidly increased the frequency of the Iso1016 allele. Bioassays of F(3) offspring arising from permethrin susceptible Val1016 homozygous parents and permethrin resistant Iso1016 homozygous parents show that Iso1016 segregates as a recessive allele in conferring kdr. Analysis of segregation between alleles at the 1011 and 1016 codons in the F(3) showed a high rate of recombination even though the two codons are only separated by a ~250 bp intron. The tools and information presented provide a means for early detection and characterization of kdr that is critical to the development of strategies for resistance management.

Application of the pupal/demographic-survey methodology in an area of Havana, Cuba, with low densities of Aedes aegypti (L.).

Between the April and December of 2004, an Aedes aegypti (L.) pupal/demographic survey was conducted in the Playa municipality of Havana. The aims were to identify the key types of container in the production of the adult mosquitoes (and so provide a basis for targeted control) and assess transmission risk in terms of the number of pupae/person. Pupal abundance, as measured in the survey, was compared with traditional Stegomyia indices. The immature stages of Ae. aegypti were only found in 70 of the 15,153 containers that were investigated and the pupae of this species were only seen in 52 of the containers. Ground-level water-storage tanks yielded 74.1% of all the pupae, with a further 19.0% found in miscellaneous small containers. The utility of the pupal/demographic-survey methodology in the evaluation of dengue risk in the study area, and other areas of Cuba with low densities of Ae. aegypti, is discussed.

Prediction of aided preferred listening levels for hearing aid gain prescription.

Relative accuracy was assessed for two methods for predicting preferred listening levels as estimated by measurements of the upper limit of the comfortable loudness range (ULCL). Sixteen hearing-impaired subjects provided ULCL data for eight test stimuli on each of five occasions. The stimuli were four narrow bands of noise centered at 500, 1000, 2000, and 4000 Hz and four narrow bands of speech babble also centered at 500, 1000, 2000, and 4000 Hz. Best estimates of ULCL were determined to be the means of the five measurements for each subject for each of the eight test signals. Results revealed that the mean ULCL for each speech-band stimulus was predicted more accurately from that subject's first measurement of ULCL for that speech-band than from his/her threshold for the same signal. However, the accuracy with which noise-band ULCLs could be used to predict the mean speech-band ULCL varied with frequency and with the number of trials averaged. Relationship of ULCL to preferred listening levels was explored by comparing results obtained in this study with work of previous investigators. Implications of the results for hearing aid gain prescription are discussed.

Relationship between two measures of aided binaural advantage.

The relationship between aided binaural squelch measured using a conventional paradigm and binaural squelch inferred from the ability to detect an intelligibility difference between binaural and pseudobinaural stimuli (presumably utilizing interaural time and intensity cues) was investigated. The conventional measures of aided binaural squelch included the NU-6 monosyllables and the high-predictability sentences from the revised SPIN test. For each measure, binaural squelch was derived by comparing the binaural intelligibility of speech-in-babble with corresponding monaural scores. Subjects were also asked to select the more intelligible hearing-aid-processed speech sample when presented with a paired-comparison task in which each pair consisted of a binaural and a pseudobinaural stimulus. Ability to choose the binaural stimulus as most intelligible was considered to be evidence of binaural squelch ability. Although the hearing-impaired subjects demonstrated typical binaural squelch for the conventional speech tests, they were usually unable to distinguish between the binaural/pseudobinaural pairs. These results suggest that (a) binaural squelch measured using conventional procedures does not necessarily quantify the listener's ability to profit from interaural differences, and (b) many hearing-impaired individuals may be unable to utilize interaural differences to enhance speech intelligibility in noise.

Effects of three organophosphorus insecticides in the reproductive potential of Culex quinquefasciatus.

A Culex quinquefasciatus Say 1823 strain with resistant genes to organophosphates was tested in the laboratory to know the reproductive potential after exposure, as larvae, at the LC30 and LC70 (mg/l) of three organophosphorus insecticides: malathion, chlorpyrifos and methyl-pirimiphos. Data showed that fecundity was decreased significantly by malathion at LC30 = 0.0025 and LC70 = 0.0075, whereas fertility has a no significant decrement by chlorpyrifos and methyl-pirimiphos at the LC70 (0.000016, 0.00043). The sexual index was affected by chlorpyrifos and methyl-pirimiphos showing a greater number of adult females.

[The selection of a strain of Culex quinquefasciatus resistant to lambdacyhalothrin and its spectrum of cross-resistance to other insecticides]. / Selección de una cepa de Culex quinquefasciatus resistente a lambdacialotrina y su espectro de resistencia cruzada a otros insecticidas.

A field strain of Culex quinquefasciatus resistant to pyrethroid lambda-cyhalothrin insecticide was selected to be used as a reference strain in the laboratory for conducting studies of biochemistry and genetics of resistance, to evaluate the utility of this insecticide for the control of mosquitoes in Cuba, and to determine the cross resistance to organophosphate insecticides, pyrethroids and a carbamate. A high resistance to lambdacyhalothrin was obtained after 6 generations of selective pressure. Lowe or no cross resistance to other pyrethroids (deltamethrin and cypermethrin), to a carbamate (propoxur) and to the organophosphate insecticides (clorpirifos and methyl-pyrimifos) was observed. A high cross resistance to malathion (organophosphate) was detected.

[Resistance in a strain of Culex quinquefasciatus coming from Medellín, Colombia]. / Estudio de la resistencia en una cepa de Culex quinquefasciatus, procedente de Medellín, Colombia.

The levels of susceptibility and/or resistance to 5 organophosphate insecticides (malathion, methyl-pyrimifos, clorpirifos, temephos and fenthion), 4 pyrethroids (cypermethrin, deltamethrin, permethrin and lambda-cyhalothrin), and a carbamate (propoxur) were determined in order to know the state of resistance in a strain of Culex quinquefasciatus from a locality of the city of Medellín, Colombia. Resistance to all organophosphate insecticides, though with relatively lower values for methyloirimifos and fenthion, was observed. No resistance to lambda-cyhalothrin and cypermethrin or to propoxur was found. These insecticides may be useful for the control of mosquitoes in Colombia. It was demonstrated by using the piperonil butoxide synergist that the oxidases of multiple function played an important role in the resistance to organophosphate insecticides and pyrethroids. The utilization of S.S.S. tributyl phosphotritiate revealed that the superproduction of unspecific esterases was a mechanism of resistance to organophosphate insecticides, except methyl-pirimifos and for perythroids, except lambda-cyhalothrin. This result should be taken into consideration for the strategies to be used to control Culex quinquefasciatus in Colombia. These two mechanism of resistance are not responsible for the resistance to propoxur. The electrophoretic analysis showed the presence of esterases B1, A6 and B6, which seem to have an important function in resistance.