ABSTRACT
Objective:To research on the immune recognition mechanism of synthetic pyrethroids and generic specific antibody.Methods:We studied on quantitative structure-activity relationship ( QSAR ) of synthetic pyrethroids and their analogs as well as antibody activity ( IC50:fifty percent inhibition concentration ) using stepwise multiple linear regression method.Based on calculating structure descriptors of synthetic pyrethroids and their analogs , two-demensional QSAR ( 2D-QSAR ) model was established.The main factors affecting antibody activity were screened using 2D-QSAR,and predictive ability of QSAR models were evaluated by the method of leave-one-out( LOO) cross-validation.Meanwhile, the structure parameters of synthetic pyrethroid fragments were calculated and then analyzed using partial least squares ( PLS) assay.And then hologram QSAR ( H-QSAR) model was constructed on molecular substructure and antibody activity.The fragments contribution to antibody activity were illustrated by encoding different colors.Results:Decision coefficent (R2) of 2D-QSAR model and HQSAR model were 0.920 and 0.917 individually,cross-validation coefficient ( Q2 ) of two QSAR models were 0.875 and 0.660 respectively ,which showed two models had good predictive abil-ity.The result from 2D-QSAR model was also obtained that smaller was hydrophobicity of pyrethroids , easier was recognized by antibody.In addition,the optimum HQSAR model was constructed after we tried many combinations of these parameters .The fragment size in optimum HQSAR model was between 4 to 10,a hologram length was 61,optimum principle component was 4,and the fragment type of B/C/Ch was selected.However ,the fingerprint encoded results of synthetic pyrethroids weren′t consistent completely with exper-imental IC50 values.Conclusion:Hydrophobicity of synthetic pyrethroids is the largest correlation factors in antibody recognization .
ABSTRACT
Cattle ticks Rhipicephalus (Boophilus) microplus are mainly controlled in Brazil by means of acaricide products, without any official policies in this regard. Acaricides continue to be sold indiscriminately, and this has contributed towards making the problem of resistance widespread, thus making diagnosis and monitoring of tick resistance essential. Here, bioassays (larval packet test) were performed on tick populations from the states of Rio Grande do Sul and Mato Grosso do Sul regarding their susceptibility to cypermethrin, deltamethrin and flumethrin. All the tick samples tested showed resistance to cypermethrin (10) (resistance factor (RF) ranging from 5.6 to 80.3) and deltamethrin (10) (RF ranging from 2.4 to 83.1). Six out of eight populations were resistant to flumethrin (RF ranging from 3.8 to 8.2). PCR molecular analyses did not show any T2134A mutations in the voltage-gated sodium channel gene, in any of the sampled populations. The results from this study highlight the critical status of resistance of the cattle tick to synthetic pyrethroids in the regions studied. Further studies are needed to identify the mechanisms responsible for the resistant phenotypes observed in the bioassays. This was the first detection of flumethrin resistance in Brazil.
O controle do carrapato Rhipicephalus (Boophilus) microplus no Brasil é feito principalmente com produtos acaricidas, sem uma política de controle oficial. A venda destes produtos continua ocorrendo de maneira indiscriminada, o que tem contribuído para generalizar o problema da resistência em todo o país, tornando essencial seu diagnóstico e monitoramento. Bioensaios (teste do pacote de larvas) foram conduzidos com populações de carrapatos do Rio Grande do Sul e Mato Grosso do Sul, com relação à sua suscetibilidade a três princípios ativos piretróides. Todas as amostras analisadas mostraram resistência à cipermetrina (10), com fatores de resistência (FR) de 5,6 a 80,3, e à deltametrina, com FR variando de 2,4 a 83,1. Seis das oito amostras foram resistentes à flumetrina (FR de 3,8 a 8,2). Análises moleculares utilizando PCR demonstraram que em todas as populações amostradas não foram encontrados alelos com a mutação T2134A no gene do canal de sódio controlado por voltagem. Os resultados deste estudo evidenciam a situação crítica da resistência do carrapato bovino ao grupo dos piretróides sintéticos nas regiões estudadas. Novos estudos são necessários para identificar os mecanismos responsáveis pelos fenótipos resistentes observados nos bioensaios. Este é o primeiro relato da resistência a flumetrina no Brasil.
Subject(s)
Animals , Insecticides/pharmacology , Pyrethrins/pharmacology , Rhipicephalus/drug effects , Brazil , Insecticide Resistance , Mutation , Rhipicephalus/geneticsABSTRACT
Aims: The aim of the study was to evaluate the field performance of insecticide-treated mosquito nets (ITNs) in north-western Burkina Faso. Study design: Cross-sectional survey. Place and Duration: The study took place between September and November 2008 (end of rainy season) in rural north-western Burkina Faso. Methodology: Standard WHO bioassays were performed on field-collected ITNs from three areas of different insecticide pressure: semi-urban Nouna town, three villages with cotton agriculture, and three villages without cotton agriculture. Data on age and washing frequency of ITNs was collected, and deltamethrin content was determind by HPLC. Results: The mean age of field-collected ITNs was 2.1 years. The mosquito mortality rate (Anopheles gambiae sl.) after 24 hours was 4% for the negative controls, 90% for the positive controls, and 73% for field-used ITNs. Differences in mosquito mortality between sub-areas disappeared after controlling for confounding variables. Conclusion: This study demonstrates that under real life conditions, deltamethrin still shows some level of effectiveness despite ongoing insecticide pressure. However, deltamethrin resistance has been observed in other parts of the country and thus close surveillance of ITN efficacy is needed. More frequent replacement of ITNs is also recommended.