Amazonian malaria: Asymptomatic human reservoirs, diagnostic challenges, environmentally driven changes in mosquito vector populations, and the mandate for sustainable control strategies

Across the Americas and the Caribbean, nearly 561,000 slide-confirmed malaria infections were reported officially in 2008. The nine Amazonian countries accounted for 89% of these infections; Brazil and Peru alone contributed 56% and 7% of them, respectively. Local populations of the relatively neglected parasite Plasmodium vivax, which currently accounts for 77% of the regional malaria burden, are extremely diverse genetically and geographically structured. At a time when malaria elimination is placed on the public health agenda of several endemic countries, it remains unclear why malaria proved so difficult to control in areas of relatively low levels of transmission such as the Amazon Basin. We hypothesize that asymptomatic parasite carriage and massive environmental changes that affect vector abundance and behavior are major contributors to malaria transmission in epidemiologically diverse areas across the Amazon Basin. Here we review available data supporting this hypothesis and discuss their implications for current and future malaria intervention policies in the region. Given that locally generated scientific evidence is urgently required to support malaria control interventions in Amazonia, we briefly describe the aims of our current field-oriented malaria research in rural villages and gold-mining enclaves in Peru and a recently opened agricultural settlement in Brazil. (C) 2011 Elsevier B.V. All rights reserved.

Dispersión y genes relacionados con la resistencia a insecticidas en Triatoma infestans: su vinculación con el control del vector de la enfermedad de Chagas

Entre las especies transmisoras de la enfermedad de Chagas de mayor importancia a nivel sanitario se destaca Triatoma infestans, considerada el principal vector en América del Sur (entre las latitudes 10° y 46° S). Los programas de control de la transmisión de la enfermedad promueven la eliminación de las poblaciones del vector T. infestans mediante la fumigación con insecticidas en las regiones endémicas. Sin embargo, esta estrategia, presenta dificultades debido en parte a la extensión y variabilidad de las áreas endémicas y por otro lado, al tiempo requerido para prevenir la recuperación de las poblaciones tratadas con insecticidas. La efectividad a largo plazo de las campañas de control es en gran medida dependiente del conocimiento de la estructura de las poblaciones del vector. El análisis de la estructura genética con un enfoque filogeográfico de poblaciones del vector en regiones endémicas de Argentina, mediante secuencias de genes mitocondriales y nucleares descriptas por primera vez para ese fin, permitirá aportar nuevas bases para la comprensión de la dinámica y evolución de las poblaciones del insecto vector y resolver interrogantes sobre procesos como por ejemplo los de dispersión y recolonización de la especie transmisora que afectan en forma directa a la eficiencia de los intentos de control. Los patrones de dispersión de esta especie estarían estrechamente vinculados con la transmisión de la enfermedad de Chagas. Por lo tanto, esta información podría ser de utilidad para la optimización del diseño de las intervenciones de control a implementar en el área endémica que conducirían a una disminución del impacto que esta enfermedad provoca en la población. Por otra parte, se han observado fallas en el control del vector debido a la existencia de resistencia a los insecticidas piretroides. Entre los mecanismos que confieren resistencia a insecticidas se han descripto los que implican cambios en canales de sodio, conocido como resistencia “knockdown” (Kdr), y aquellos que provocan un aumento de la actividad de enzimas responsables de su metabolismo. Con respecto al último mecanismo, las evidencias sugieren que las enzimas mono-oxigenasas citocromo P450 tienen comunmente un rol primario en la resistencia a insecticidas piretroides. Incrementos en la expresión a nivel de la transcripción de genes de citocromos P450 (CYP450) son frecuentemente considerados responsables de aumentar el metabolismo de insecticidas y parece ser un fenómeno común en la evolución del desarrollo de resistencia en insectos. El estudio de la posible relación de genes CYP450, que proponemos caracterizar en T. infestans, con la resistencia a insecticidas podría aportar nuevas bases para el desarrollo del manejo de esa resistencia. Sin embargo, mientras que existen múltiples genes CYP450 en el genoma de insectos, sólo un gen NADPH citocromo P450 reductasa (CPR) existe en el genoma de cada insecto. Por este motivo, se propone también caracterizar en el vector este gen que codifica para una enzima que actúa en la transferencia de electrones desde la forma reducida de NADPH a los citocromos P450, así como investigar el efecto de su silenciamiento en poblaciones de T. infestans resistentes a insecticidas piretroides. Además, con el propósito de analizar si la existencia de resistencia a insecticidas piretroides puede ser el resultado de la acción de los citocromo P450 y/o de otros factores, se investigará en las poblaciones resistentes la posible existencia de una mutación de un gen de canal de sodio relacionada con resistencia a insecticidas (Kdr) que ha sido descripta para T. infestans. Este estudio proveería información de utilidad para el desarrollo de estrategias alternativas de control que serían de suma importancia en regiones en las que las poblaciones de este vector presentan resistencia a los insecticidas y, por lo tanto, tendría claramente implicancias importantes para el manejo de la resistencia en este vector.

Epidemiology and control of vector-borne diseases /

Bibliography: p. 37-38.

Prevention and control of vector problems.

Mode of access: Internet.

Aedes aegypti pharate first instar aseasonal quiescence cues anticipatory plasticity with implications for urban vector ecology and control

The eggs of the dengue fever vector Aedes aegypti possess the ability to undergo an extended quiescence period hosting a fully developed first instar larvae within its chorion. As a result of this life history stage, pharate larvae can withstand months of dormancy inside the egg where they depend on stored reserves of maternal origin. This adaptation known as pharate first instar quiescence, allows A. aegypti to cope with fluctuations in water availability. An examination of this fundamental adaptation has shown that there are trade-offs associated with it. ^ Aedes aegypti mosquitoes are frequently associated with urban habitats that may contain metal pollution. My research has demonstrated that the duration of this quiescence and the extent of nutritional depletion associated with it affects the physiology and survival of larvae that hatch in a suboptimal habitat; nutrient reserves decrease during pharate first instar quiescence and alter subsequent larval and adult fitness. The duration of quiescence compromises metal tolerance physiology and is coupled to a decrease in metallothionein mRNA levels. My findings also indicate that even low levels of environmentally relevant larval metal stress alter the parameters that determine vector capacity. ^ My research has also demonstrated that extended pharate first instar quiescence can elicit a plastic response resulting in an adult phenotype distinct from adults reared from short quiescence eggs. Extended pharate first instar quiescence affects the performance and reproductive fitness of the adult female mosquito as well as the nutritional status of its progeny via maternal effects in an adaptive manner, i.e., anticipatory phenotypic plasticity results as a consequence of the duration of pharate first instar quiescence and alternative phenotypes may exist for this mosquito with quiescence serving as a cue possibly signaling the environmental conditions that follow a dry period. M findings may explain, in part, A. aegypti's success as a vector and its geographic distribution and have implications for its vector capacity and control.^

The Repellent DEET Potentiates Carbamate Effects via Insect Muscarinic Receptor Interactions: An Alternative Strategy to Control Insect Vector-Borne Diseases.

International audience

Aislamiento, producción y evaluación de la patogenicidad de cepas de Hirsutella citriformis Speare para el control de Diaphorina citri Kuwayama, vector de la enfermedad Huanglongbing de los cítricos

La industria citrícola es una de las más importantes industrias con las que cuenta el país y en los últimos años se encuentra amenazada por una plaga que está ocasionando estragos en todas las áreas citrícolas en México, el Huanglongbing o greening la cual es transmitida por el psílido asiático de los cítricos, Diaphorina citri Kuwayama, insecto que ocasiona daño en las plantas al alimentarse de los brotes tiernos y que además es el vector de la bacteria Candidatus Liberibacter asiaticus para la cual no hay cura y por lo que es necesario controlar al insecto que la transmite. Por lo que el presente trabajo consistió en aislar hongos de D. citri micosados, identificarlos en base a sus características morfométricas y usando técnicas moleculares, cultivarlos en diferentes medios de cultivo comerciales de agar para seleccionar aquel en el cual crecen y conidian mejor, se determinó también el tipo de exudados producidos por Hirsutella citriformis en los medios de agar, se cultivaron en dos diferentes medios de cultivo líquido y un sustrato vegetal para obtener mayor cantidad de conidios; también se realizaron bioensayos de laboratorio para determinar la virulencia de las cepas y seleccionar aquellas que pudieran controlar mejor al insecto; se evaluó la patogenicidad que pudieran presentar sobre insectos depredadores de D. citri, y con los resultados obtenidos se seleccionó las cepas que presentaron mayor patogenicidad sobre el insecto vector del HLB para evaluar su actividad sobre el mismo en bioensayo de campo. Se aislaron cinco cepas de insectos micosados provenientes de diferentes regiones citrícolas, se trabajó con ellos además de tres cepas con las cuales ya contaba el INIFAP de General Terán de Nuevo León. Se identificaron morfométrica y molecularmente como Hirsutella citriformis Speare. Los medio comerciales de cultivo en los cuales crecen y presentan mejor conidiación son los medios agar papa dextrosa enriquecidos con extracto de levadura al 0.5 y 1 % en los cuales se obtuvo un crecimiento radial de 3.2 a 3.8 cm para las cepas IB-Hir-2 e INIFAP-Hir-1 respectivamente, a los 34 días de cultivo a 25 ± 1 °C. La conidiación obtenida para las ocho cepas no correspondió al crecimiento radial, pero si concordó en presentarse en los medios enriquecidos con extracto de levadura, los valores variaron desde 1.22 x 10⁶ a 2.79 x 10⁷ para las cepas 2 INIFAP-Hir-2 en agar papa dextrosa e IB-Hir-2 en agar papa dextrosa con extracto de levadura al 1% respectivamente. En medios líquidos la mayor producción de blastosporas obtenida fue 4.3 x 108 blastosporas /ml a los 9 días en el medio de casaminoácidos para la cepa INIFAP-Hir-1, y en caldo papa dextrosa la mayor producción la presentó a los 11 días la cepa IB-Hir-2 (7.7 x 107 blastosporas/ml). La mayor producción de conidios en el sustrato vegetal (arroz) se obtuvo a los 14 días por la cepa INIFAP-Hir-4 (1.97 x 107 conidios/gr). Se analizaron los dos tipos de exudados observados en las cepas usando los métodos de Bradford para proteínas y el del Fenol Sulfúrico para carbohidratos y con estos métodos se determinó que todas las cepas producen ambos tipos de compuestos, además de que las proteínas son los exudados amarillo claro y oscuro, mientras que los carbohidratos corresponden a las gotas cristalinas producidas por las cepas en los diferentes medios de agar. En los diferentes bioensayos de laboratorio las cepas presentaron mayor mortalidad cuando se inoculó por contacto, donde las cepas INIFAP-Hir-1, INIFAP-Hir-2, IB-Hir-1 e IB-Hir-2 mostraron los mayores porcientos de mortalidad media. Al evaluar la patogenicidad de cuatro cepas sobre dos depredadores de D. citri, los resultados fueron similares para tratamientos y testigo y no se presentó micosamiento en los insectos muertos. Bajo condiciones de laboratorio la CL50 y CL90 obtenidas para el aislado INIFAP-Hir-1 fueron, 34 x 105 y 26.7 x 107 respectivamente. En el bioensayo de campo se usaron las cepas INIFAP.Hir-2, INIFAP.Hir-4, IB-Hir-1 e IB-Hir-2 y el mayor porciento de mortalidad obtenida fue 51.049 y el menor 35.7 para las cepas INIFAP-Hir-4 e IB-Hir-1 respectivamente, mientras que el testigo con adherente mostro 6.059 y en el testigo absoluto 4.84 % de mortalidad promedio. Además logramos aislar la cepa que los micosaba de 20 insectos colectados en diferentes puntos de muestreo, identificando en base a sus características morfológicas de crecimiento colonial a tres de las cepas evaluadas y a la cepa nativa de Martínez de la Torre.

Aedes aegypti Pharate First Instar Aseasonal Quiescence Cues Anticipatory Plasticity with Implications for Urban Vector Ecology and Control

The eggs of the dengue fever vector Aedes aegypti possess the ability to undergo an extended quiescence period hosting a fully developed first instar larvae within its chorion. As a result of this life history stage, pharate larvae can withstand months of dormancy inside the egg where they depend on stored reserves of maternal origin. This adaptation known as pharate first instar quiescence, allows A. aegypti to cope with fluctuations in water availability. An examination of this fundamental adaptation has shown that there are trade-offs associated with it. Aedes aegypti mosquitoes are frequently associated with urban habitats that may contain metal pollution. My research has demonstrated that the duration of this quiescence and the extent of nutritional depletion associated with it affects the physiology and survival of larvae that hatch in a suboptimal habitat; nutrient reserves decrease during pharate first instar quiescence and alter subsequent larval and adult fitness. The duration of quiescence compromises metal tolerance physiology and is coupled to a decrease in metallothionein mRNA levels. My findings also indicate that even low levels of environmentally relevant larval metal stress alter the parameters that determine vector capacity. My research has also demonstrated that extended pharate first instar quiescence can elicit a plastic response resulting in an adult phenotype distinct from adults reared from short quiescence eggs. Extended pharate first instar quiescence affects the performance and reproductive fitness of the adult female mosquito as well as the nutritional status of its progeny via maternal effects in an adaptive manner, i.e., anticipatory phenotypic plasticity results as a consequence of the duration of pharate first instar quiescence and alternative phenotypes may exist for this mosquito with quiescence serving as a cue possibly signaling the environmental conditions that follow a dry period. M findings may explain, in part, A. aegypti’s success as a vector and its geographic distribution and have implications for its vector capacity and control.

Artificial Lighting as a Vector Attractant and Cause of Disease Diffusion

BACKGROUND: Traditionally, epidemiologists have considered electrification to be a positive factor. In fact, electrification and plumbing are typical initiatives that represent the integration of an isolated population into modern society, ensuring the control of pathogens and promoting public health. Nonetheless, electrification is always accompanied by night lighting that attracts insect vectors and changes people's behavior. Although this may lead to new modes of infection and increased transmission of insect-borne diseases, epidemiologists rarely consider the role of night lighting in their surveys. OBJECTIVE: We reviewed the epidemiological evidence concerning the role of lighting in the spread of vector-borne diseases to encourage other researchers to consider it in future studies. DISCUSSION: We present three infectious vector-borne diseases-Chagas, leishmaniasis, and malaria-and discuss evidence that suggests that the use of artificial lighting results in behavioral changes among human populations and changes in the prevalence of vector species and in the modes of transmission. CONCLUSION: Despite a surprising lack of studies, existing evidence supports our hypothesis that artificial lighting leads to a higher risk of infection from vector-borne diseases. We believe that this is related not only to the simple attraction of traditional vectors to light sources but also to changes in the behavior of both humans and insects that result in new modes of disease transmission. Considering the ongoing expansion of night lighting in developing countries, additional research on this subject is urgently needed.

Digital control and integration of a 192 MW wind farm with doubly fed induction generator into the Brazilian power system

This paper reports on design of digital control for wind turbines and its relation to the quality of power fed into the Brazilian grid on connecting to it a 192 MW wind farm equipped with doubly fed induction generators. PWM converters are deployed as vector controlled regulated current voltage sources for their rotors, for independent control of both active and reactive power of those generators. Both speed control and active power control strategies are analyzed, in the search for maximum efficiency of conversion of wind kinetic energy into electric power and enhanced quality of delivered power. (C) 2009 Elsevier B.V. All rights reserved.

Distributed power control algorithm for multiple access systems based on Verhulst model

In this paper the continuous Verhulst dynamic model is used to synthesize a new distributed power control algorithm (DPCA) for use in direct sequence code division multiple access (DS-CDMA) systems. The Verhulst model was initially designed to describe the population growth of biological species under food and physical space restrictions. The discretization of the corresponding differential equation is accomplished via the Euler numeric integration (ENI) method. Analytical convergence conditions for the proposed DPCA are also established. Several properties of the proposed recursive algorithm, such as Euclidean distance from optimum vector after convergence, convergence speed, normalized mean squared error (NSE), average power consumption per user, performance under dynamics channels, and implementation complexity aspects, are analyzed through simulations. The simulation results are compared with two other DPCAs: the classic algorithm derived by Foschini and Miljanic and the sigmoidal of Uykan and Koivo. Under estimated errors conditions, the proposed DPCA exhibits smaller discrepancy from the optimum power vector solution and better convergence (under fixed and adaptive convergence factor) than the classic and sigmoidal DPCAs. (C) 2010 Elsevier GmbH. All rights reserved.

Characterization of electrical penetration graphs of Bucephalogonia xanthophis, a vector of Xylella fastidiosa in citrus

The sharpshooter Bucephalogonia xanthophis (Berg) (Homoptera: Cicadellidae) is a vector of the xylem-limited bacterium, Xylella fastidiosa (Wells, Raju, Hung, Weisburg, Mandelco-Paul, and Brenner), which causes citrus variegated chlorosis. Despite the importance of citrus variegated chlorosis, the probing behavior of vectors on citrus and its implications for transmission of X. fastidiosa have not been studied. Here we studied electrical penetration graph (EPG-DC system) waveforms produced by B. xanthophis on Citrus sinensis (L.) Osbeck (Rutaceae), and their relationships with stylet activities and xylem ingestion. Electrical penetration graph waveforms were described based on amplitude, frequency, voltage level, and electrical origin of the observed traces during stylet penetration on plant tissues. The main waveforms were correlated with histological observations of salivary sheaths in plant tissues and excretion analysis, in order to determine stylet activities and their precise position. Six waveforms and associated activities are described: (S) secretion of salivary sheath and intracellular stylet pathway, (R) resting during stylet pathway, (Xc) contact of stylets with xylem vessels, (Xi) active xylem ingestion, (N) interruption within the xylem phase (during Xc or Xi), and (W) withdrawal of stylet from the plant. The sharpshooter spent 91.8% of its probing time with its stylet in the xylem, where the main activity was ingestion (Xi: 97.5%). During a probe, the most likely sequence of events is secretion of salivary sheath and pathway (S) through epidermal and parenchyma cells (all individuals), followed by contact with xylem (Xc) (67.6% of all individuals) and ingestion (Xi) (88.3% of those that exhibit waveform Xc). The mean time to contact the xylem (Xc) and initiate ingestion (Xi) after onset of the first probe was 27.8 and 34.2 min, respectively. However, sustained xylem ingestion (Xi > 5 min) was established after 39.8 min, on average. This information is basic for future studies on the transmission mechanisms of X. fastidiosa and in order to establish control strategies aimed at interfering with this process.

Gene transfer and expression of a non-viral polycation-based vector in CD4(+) cells

CD4-selective targeting of an antibody-polycation-DNA complex was investigated The complex was synthesized with the anti-CD4 monoclonal antibody B-F5, polylysine(268) (pLL) and either the pGL3 control vector containing the luciferase reporter gene or the pGeneGrip vector containing the green fluorescent protein (GFP) gene. B-F5-pLL-DNA complexes inhibited the binding of I-125-B-F5 to CD4(+) Jurkat cells, while complexes synthesised either without B-F5 or using a non-specific mouse IgG1 antibody had little or no effect Expression of the luciferase reporter gene was achieved in Jurkat cells using the B-F5-pLL-pGL3 complex and was enhanced in the presence of PMA. Negligible luciferase activity was defected with the non-specific antibody complex in Jurkat cells or with the B-F5-pLL-pGL3 complex in the CD4(-) K-562 cells. Using complexes synthesised with the pGeneGrip vector, the transfection efficiency in Jurkat and K-562 cells was examined using confocal microscopy. More than 95% of Jurkat cells expressed GFP and the level of this expression was markedly enhanced by PMA. Negligible GFP expression was seen in K-562 cells or when B-F5 was replaced by a nonspecific antibody. Using flow cytometry, fluorescein-labelled complex showed specific targeting to CD4(+) cells in a mixed cell population from human peripheral blood. These studies demonstrate the selective transfection of CD4(+) T-lymphoid cells using a polycation-based gene delivery system. The complex may provide a means of delivering anti-HIV gene therapies to CD4(+) cells in vivo.

Endostatin- and interleukin-2-expressing retroviral bicistronic vector for gene therapy of metastatic renal cell carcinoma

Background Metastatic renal cell carcinoma (mRCC) is one of the most treatment-resistant malignancies. Despite all new therapeutic advances, almost all patients develop resistance to treatment and cure is rarely seen. In the present study, we evaluated the antitumor effect of a bicistronic retrovirus vector encoding both endostatin (ES) and interleukin (IL)-2 using an orthotopic metastatic RCC mouse model. Methods Balb/C-bearing Renca cells were treated with NIH/3T3-LendIRES-IL-2-SN cells. In the survival studies, mice were monitored daily until they died. At the end of the in vivo experiment, serum levels of IL-2 and ES were measured, the lung was weighed, and the number of metastatic nodules, nodule area, tumor vessels and proliferation of tumor-infiltrating Renca cells were determined. Results Inoculation of NIH/3T3-LendIRES-IL-2-SN cells resulted in an increase in ES and IL-2 levels in the treated group (p < 0.05). There was a significant decrease in lung wet weight, lung nodule area and tumor vessels in the treated group compared to the control group (p < 0.001). The proliferation of Renca cells in the bicistronic-treated group was significantly reduced compared to the control group (p < 0.05). Kaplan-Meier survival curves showed that the probability of survival was significantly higher for mice submitted to bicistronic therapy (log-rank test, p = 0.0016). Bicistronic therapy caused an increase in the infiltration of CD4, CD4 interferon (IFN)gamma-producing, CD8, CD8 IFN gamma-producing and natural killer (CD49b) cells. Conclusions Retroviral bicistronic gene transfer led to the secretion of functional ES and IL-2 that was sufficiently active to: (i) inhibit tumor angiogenesis and tumor cell proliferation and (ii) increase the infiltration of immune cells (C) Copyright. 2011 John Wiley & Sons, Ltd.