A comparison of DNA sequencing and the hydrolysis probe analysis (TaqMan assay) for knockdown resistance (kdr) mutations in Anopheles gambiae from the Republic of the Congo

<p>Abstract</p> <p>Background</p> <p>Knockdown resistance (<it>kdr</it>) caused by a single base pair mutation in the sodium channel gene is strongly associated with pyrethroid insecticide resistance in <it>Anopheles gambiae </it>in West-Central Africa. Recently, various molecular techniques have been developed to screen for the presence of the <it>kdr </it>mutations in vector populations with varying levels of accuracy. In this study, the results of the hydrolysis probe analysis for detecting the <it>kdr </it>mutations in <it>An. gambiae </it>s.s. from the Republic of the Congo were compared with DNA sequence analysis.</p> <p>Methods</p> <p>A total of 52 pyrethroid and DDT resistant <it>An. gambiae </it>from Pointe-Noire (Congo-Brazzaville) were tested for detection of the two <it>kdr </it>mutations (<it>kdr</it>-e and <it>kdr</it>-w) that are known to occur in this species. Results from the hydrolysis probe analysis were compared to DNA sequencing to verify the accuracy of the probe analysis for this vector population.</p> <p>Results</p> <p>Fifty-one specimens were found to be <it>An. gambiae </it>S-form and one was a M/S hybrid. DNA sequencing revealed that more than half of the specimens (55.8%) carried both the <it>kdr</it>-e and <it>kdr</it>-w resistance mutations, seven specimens (13.5%) were homozygous for the <it>kdr</it>-e mutation, and 14 specimens (26.9%) were homozygous for the <it>kdr</it>-w mutation. A single individual was genotyped as heterozygous <it>kdr</it>-e mutation (1.9%) only and another as heterozygous <it>kdr</it>-w mutation (1.9%) only. Analysis using hydrolysis probe analysis, without adjustment of the allelic discrimination axes on the scatter plots, revealed six specimens (11.5%) carrying both mutations, 30 specimens (57.8%) as homozygous <it>kdr</it>-w, six specimens (11.5%) homozygous for the <it>kdr</it>-e mutation, one specimen (1.9%) heterozygous for the <it>kdr</it>-w mutation and one specimen (1.9%) present in wild type form. Eight of the specimens (15.4%) could not be identified using unadjusted hydrolysis probe analysis values. No heterozygous <it>kdr</it>-e mutations were scored when adjustment for the allelic discrimination axes was omitted. However, when the axes on the scatter plots were adjusted the results were consistent with those of the DNA sequence analysis, barring two individuals that were mis-scored in the hydrolysis probe analysis.</p> <p>Conclusion</p> <p>Both the <it>kdr</it>-e and <it>kdr</it>-w mutations were abundant in <it>An. gambiae </it>S-form from Pointe-Noire. The hydrolysis probe analysis can lead to misleading results if adjustment to allelic discrimination axes is not investigated. This is mainly relevant when both <it>kdr</it>-e and <it>kdr</it>-w are present in a population in a high frequency. This report highlights the importance of concurrent screening for both mutations. Therefore, performing routine assay protocols blindly can result in the misinterpretation of results. Although hydrolysis probe analysis of <it>kdr </it>is still held as the gold standard assay, this paper highlights the importance of <it>kdr </it>mutation confirmation via sequencing especially in regions where <it>kdr </it>frequency has never been reported before or where both the <it>kdr</it>-e and <it>kdr</it>-w mutations are present simultaneously.</p

Electron beam induced current in InSb-InAs nanowire type-III heterostructures

InSb-InAs nanowire heterostructure diodes investigated by electron beam induced current (EBIC) demonstrate an unusual spatial profile where the sign of the EBIC signal changes in the vicinity of the heterointerface. A qualitative explanation confirmed by theoretical calculations is based on the specific band diagram of the structure representing a type-III heterojunction with an accumulation layer in InAs. The sign of the EBIC signal depends on the specific parameters of this layer. In the course of measurements, the diffusion length of holes in InAs and its temperature dependence are also determined

Electrical properties and band diagram of InSb-InAs nanowire type-III heterojunctions

The electrical properties of nanowire-based n-InSb-n-InAs heterojunctions were investigated theoretically and experimentally. Analysis of the current-voltage characteristics showed that the current through the heterojunction is caused mostly by generation-recombination processes in the InSb and at the heterointerface. Due to the partially overlapping valence band of InSb and the conduction band of InAs, the second process is fast and activationless. Theoretical analysis showed that, depending on the heterojunction parameters, the flux of non-equilibrium minority carriers may have a different direction, explaining the experimentally observed non-monotonic coordinate dependence of the electron beam induced current

Bifurcations and chaos in semiconductor superlattices with a tilted magnetic field

We study the effects of dissipation on electron transport in a semiconductor superlattice with an applied bias voltage and a magnetic field that is tilted relative to the superlattice axis.In previous work, we showed that although the applied fields are stationary,they act like a THz plane wave, which strongly couples the Bloch and cyclotron motion of electrons within the lowest miniband. As a consequence,the electrons exhibit a unique type of Hamiltonian chaos, which creates an intricate mesh of conduction channels (a stochastic web) in phase space, leading to a large resonant increase in the current flow at critical values of the applied voltage. This phase-space patterning provides a sensitive mechanism for controlling electrical resistance. In this paper, we investigate the effects of dissipation on the electron dynamics by modifying the semiclassical equations of motion to include a linear damping term. We demonstrate that even in the presence of dissipation,deterministic chaos plays an important role in the electron transport process. We identify mechanisms for the onset of chaos and explore the associated sequence of bifurcations in the electron trajectories. When the Bloch and cyclotron frequencies are commensurate, complex multistability phenomena occur in the system. In particular, for fixed values of the control parameters several distinct stable regimes can coexist, each corresponding to different initial conditions. We show that this multistability has clear, experimentally-observable, signatures in the electron transport characteristics.Comment: 14 pages 11 figure

Insecticide resistance in malaria vector mosquitoes at four localities in Ghana, West Africa

<p>Abstract</p> <p>Background</p> <p>Malaria vector control programmes that rely on insecticide-based interventions such as indoor house spraying with residual insecticides or insecticide treated bed nets, need to base their decision-making process on sound baseline data. More and more commercial entities in Africa, such as mining companies, are realising the value to staff productivity of controlling malaria transmission in their areas of operation.</p> <p>This paper presents baseline entomological data obtained during surveys conducted for four mining operations in Ghana, West Africa.</p> <p>Results</p> <p>The vast majority of the samples were identified as <it>Anopheles gambiae </it>S form with only a few M form specimens being identified from Tarkwa. <it>Plasmodium falciparum </it>infection rates ranged from 4.5 to 8.6% in <it>An. gambiae </it>and 1.81 to 8.06% in <it>An. funestus</it>. High survival rates on standard WHO bioassay tests were recorded for all insecticide classes except the organophosphates that showed reasonable mortality at all locations (i.e. > 90%). The West African <it>kdr </it>mutation was detected and showed high frequencies in all populations.</p> <p>Conclusions</p> <p>The data highlight the complexity of the situation prevailing in southern Ghana and the challenges facing the malaria vector control programmes in this region. Vector control programmes in Ghana need to carefully consider the resistance profiles of the local mosquito populations in order to base their resistance management strategies on sound scientific data.</p

Zener transitions between dissipative Bloch bands. II: Current Response at Finite Temperature

We extend, to include the effects of finite temperature, our earlier study of the interband dynamics of electrons with Markoffian dephasing under the influence of uniform static electric fields. We use a simple two-band tight-binding model and study the electric current response as a function of field strength and the model parameters. In addition to the Esaki-Tsu peak, near where the Bloch frequency equals the damping rate, we find current peaks near the Zener resonances, at equally spaced values of the inverse electric field. These become more prominenent and numerous with increasing bandwidth (in units of the temperature, with other parameters fixed). As expected, they broaden with increasing damping (dephasing).Comment: 5 pages, LateX, plus 5 postscript figure

Terahertz Excitation of a Coherent -Type Three-Level System of Exciton-Polariton Modes in a Quantum-Well Microcavity

Interactions of few-cycle terahertz pulses with the induced optical polarization in a quantum-well microcavity reveal that the lower and higher exciton-polariton modes together with the optically forbidden 2p-exciton state form a unique Lambda-type three-level system. Pronounced nonlinearities are observed via time-resolved strong-terahertz and weak-optical excitation spectroscopy and explained with a fully microscopic theory. The results show that the terahertz pulses strongly couple the exciton-polariton states to the 2p-exciton state while no resonant transition between the two polariton levels is observed.Keywords: Semiconductor microcavities, Bose Einstein condensation, CotKeywords: Semiconductor microcavities, Bose Einstein condensation, Co