Invasion Zone Research Articles

Invasion of the Lyme Disease Vector Ixodes scapularis: Implications for Borrelia burgdorferi Endemicity

Lyme disease risk is increasing in the United States due in part to the spread of blacklegged ticks Ixodes scapularis, the principal vector of the spirochetal pathogen Borrelia burgdorferi. A 5-year study was undertaken to investigate hypothesized coinvasion of I. scapularis and B. burgdorferi in Lower Michigan. We tracked the spatial and temporal dynamics of the tick and spirochete using mammal, bird, and vegetation drag sampling at eight field sites along coastal and inland transects originating in a zone of recent I. scapularis establishment. We document northward invasion of these ticks along Michigan's west coast during the study period; this pattern was most evident in ticks removed from rodents. B. burgdorferi infection prevalences in I. scapularis sampled from vegetation in the invasion zone were 9.3% and 36.6% in nymphs and adults, respectively, with the majority of infection (95.1%) found at the most endemic site. There was no evidence of I. scapularis invasion along the inland transect; however, low-prevalence B. burgdorferi infection was detected in other tick species and in wildlife at inland sites, and at northern coastal sites in years before the arrival of I. scapularis. These infections suggest that cryptic B. burgdorferi transmission by other vector-competent tick species is occurring in the absence of I. scapularis. Other Borrelia spirochetes, including those that group with B. miyamotoi and B. andersonii, were present at a low prevalence within invading ticks and local wildlife. Reports of Lyme disease have increased significantly in the invasion zone in recent years. This rapid blacklegged tick invasion--measurable within 5 years--in combination with cryptic pathogen maintenance suggests a complex ecology of Lyme disease emergence in which wildlife sentinels can provide an early warning of disease emergence.

Fundamentals of coaxial and coplanar coil arrays in induction tools

Until about ten years ago, all commercial borehole induction devices were built up with the traditional coaxial coil arrays. Since then, those apparatus incorporated the unconventional coplanar coil arrays, in order to investigate thinly laminated reservoirs and to locate axially asymmetrical anomalies like vugs and fractures. In order to comprehend the fundamentals of the coplanar array in induction probes, we present a comparative study with the coaxial array through one-dimensional modeling of some borehole environments, like: 1) homogeneous, isotropic and unlimited conducting media; 2) invaded thick bed with annulus; 3) horizontal and dipping multilayer sequences; 4) gradational transition zone between two thick beds; and 5) thinly laminated formations. The comparative study allows us to conclude that: 1) the skin effect is strongest in the coplanar array responses; 2) the coplanar array responses are more sensitive to mud filtrate invasion and annulus zones, which are direct indicators of movable oil; 3) polarization horns on the coplanar array profiles can be good bed boundary indicators; 4) coplanar arrays present the greatest sensitivity to detect and delineate thinly laminated reservoirs.

Fast simulation of triaxial borehole induction measurements acquired in axially symmetrical and transversely isotropic media

We introduce and successfully test an efficient method to simulate triaxial borehole electromagnetic (EM) induction measurements acquired in axially symmetrical and transversely isotropic (TI) media. The method uses a Fourier series expansion to express the azimuthal dependence of EM fields and the source term whereby the essentially 3D problem collapses to a series of independent 2D problems. Each 2D problem is solved with a semianalytic method that uses normalized Bessel functions and normalized Hankel functions to express the radial dependence of EM fields, thereby improving numerical stability. In addition, use is made of amplitude and slope basis functions to describe the longitudinal dependence of EM fields to avoid grid refinement in the vicinity of horizontal formation boundaries. For validation, we compare the new simulation method to two 1D analytic methods in horizontally and radially layered formations, and to one 3D finite-difference method (3DFD) in multilayered formations that include borehole and invasion zones. Numerical results indicate that the method is accurate in formations with high conductivity contrasts compared to 1D methods and is more than ten times more efficient than the 3DFD method in multilayer formations.

Cellular characterization of the peritumoral edema zone in malignant brain tumors

Brain edema is a hallmark of human malignant brain tumors and contributes to the clinical course and outcome of brain tumor patients. The so-called perifocal edema or brain swelling imposes in T2-weighted MR scans as high intensity areas surrounding the bulk tumor mass. The mechanisms of this increased fluid attraction and the cellular composition of the microenvironment are only partially understood. In this study, we focus on imaging perifocal edema in orthotopically implanted gliomas in rodents and correlate perifocal edema with immunohistochemical markers. We identified that areas of perifocal edema not only include the tumor invasion zone, but also are associated with increased glial fibrillary acidic protein (GFAP) and aquaporin-4 expression surrounding the bulk tumor mass. Moreover, a high number of activated microglial cells expressing CD11b and macrophage migration inhibitory factor (MIF) accumulate at the tumor border. Thus, the area of perifocal edema is mainly dominated by reactive changes of vital brain tissue. These data corroborate that perifocal edema identified in T2-weighted MR scans are characterized with alterations in glial cell distribution and marker expression forming an inflammatory tumor microenvironment.

Computing Electromagnetic Wave Resistivity MWD Tool's Response Using Accelerated Iteration Algorithm for Integral Equations

AbstractThe 2D integral equations are computed by an integrated iteration algorithm of modified successive approximation method (MSAM) and Aitken acceleration technique. The longitudinally stratified virgin formation is taken as the background and the computational region is restricted within the borehole and invasion zone in the algorithm, thus the algorithm is qualified for the virtues of small number of unknowns, fast converging speed and high accuracy. The response of the electromagnetic wave resistivity MWD tool in cylindrically symmetrical 2D formation is simulated by the algorithm. The results have shown that the amplitude attenuation and phase shift are affected differently by the borehole, invasion and surrounding shale, and that their radial depth of investigation and vertical resolution are also different. The bed boundary can be accurately located by the crossover point of the compensated amplitude attenuation and phase shift resistivities.

Controlling invasive species in complex social landscapes

Control of biological invasions depends on the collective decisions of resource managers across invasion zones. Regions with high land‐use diversity, which we refer to as “management mosaics”, may be subject to severe invasions, for two main reasons. First, as land becomes increasingly subdivided, each manager assumes responsibility for a smaller portion of the total damages imposed by invasive species; the incentive to control invasives is therefore diminished. Secondly, managers opting not to control the invasion increase control costs for neighboring land managers by allowing their lands to act as an invader propagule source. Coordination among managers can help mitigate these effects, but greater numbers – and a wider variety – of land managers occupying a region hinder collective action. Here, we discuss the challenges posed by management mosaics, using a case study of the yellow starthistle (Centaurea solstitialis) invasion in the Sierra Nevada foothills of California. We suggest that the incorporation of management mosaic dynamics into invasive species research and management is essential for successful control of invasions, and provide recommendations to address this need.

Minimally Invasive Dorsal Root Entry Zone Operation

Minimally Invasive Dorsal Root Entry Zone Operation

Phase distribution and intrapore salt exchange during drilling mud invasion of an oil- and gas-bearing formation

As a result of drilling mud filtrate invasion of a formation saturated with oil, gas and natural water, the distribution of the immiscible phases and the electrophysical characteristics of the near-well zone change as compared with its initial state. Taking this change into account is necessary for successful interpretation of electrical well logging data. In this paper, on the basis of the equations of immiscible fluid flow through a porous medium and the system of transfer equations with account for instantaneous salt exchange between the filtrate and the natural water inside the pores, the regions of initial formation fluid saturations for which in the invasion zone the displacement fronts retain their relative position are determined.

Quantification of Overbalance-Induced Invasive Damage and the Estimation of Equivalent-Skin Effect on Production

Summary An important premise of underbalanced drilling (UBD) is the productivity improvement it delivers through mitigation of invasive damage. Characterization and quantification of such damage, therefore, becomes a prerequisite for assessing the value delivered by UBD. Several methods are available to quantify damage. In this work, we use a novel approach that combines dynamic microscale reservoir simulations calibrated to special core tests to model the extent of invasive damage and its impact on flowback during production. The approach is based on special tests conducted on the reservoir core and a dynamic "microsimulator" to model invasion during drilling. Special core tests designed to measure effects of overbalanced exposure to drilling fluids are first conducted. Inputs to the simulation model are based on careful interpretation of the core-test results, and thus are calibrated to observation. Details of the approach were presented earlier by Suryanarayana et al. (2007). In this paper, we apply this approach to two field cases and use the results to quantify the damage and its impact on production. The two field cases are discussed in detail. Both relative permeability and permanent-damage effects are described. The dramatic effects of invasion on cleanup and long-term production are illustrated, demonstrating the incremental value of UBD in these cases. Damage can be modeled as an equivalent skin, based on the saturation and permeability profiles within the zone of invasion. Because the saturation and permeability effects are a function of location along the productive length and a function of time, we obtain time-dependent and spatially dependent equivalent skin. The equivalent skin can then be used in field-scale reservoir models to compare various drilling and development options. The use of these results in designing an optimal drilling and completion plan to lock in the value of UBD is demonstrated for the two field cases.

The 3‐D Finite Difference Time Domain Algorithm of Responses of Multi‐component Electromagnetic Well Logging in a Deviated and Layered Anisotropic Formation

AbstractIn this paper, we advance an algorithm of numerical modeling for responses of multicomponent electromagnetic well logging in a deviated and layered anisotropic formation through the 3‐D finite difference time domain approach (FDTD). First, we use a Yee's staggered grid and linear interpolation formula to discretize the Maxwell equation in the time domain in an anisotropic medium and determine the non‐defined components of electromagnetic (EM) field in the staggered grid in order to obtain the time recursive equation of the EM field on all staggered grids in an arbitrary anisotropic media. At the same time, area weighted average and transformation matrix are utilized to calculate the effective conductive tensors on the grids, and an absorbing boundary condition is executed to reduce the reflection of outer‐boundary on the base of uniaxial anisotropic perfectly matched layer (UPML). Then, we apply three mutually orthogonal transmitter coils with a singlefrequency sinusoidal current to excite EM fields in the time domain and extract the amplitude and phase of EM from the EM field through a special two‐equation and two‐unknown (2E2U) approach to obtain the responses of multicomponent EM propagation logging tool. Finally, by numerical results we validate the algorithm and examine systematically the influence of changes in bed thickness, formation dipping angle and radius of invasion zones on responses of the tool.

Downregulation of SPARC expression inhibits cell migration and invasion in malignant gliomas

The secreted protein acidic and rich in cysteine (SPARC) is a secreted glycoprotein that plays an essential role in promoting the motility of invasive tumor cells. In the present study, we investigated the role of SPARC in the motile and invasive activities of human glioma cells by silencing the SPARC gene. Introduction of SPARC-targeted small interfering RNA (siRNA) into glioma cell lines resulted in downregulation of SPARC expression, and significantly suppressed glioma cell migration in vitro. Furthermore, invasiveness was significantly reduced in the cells transfected with SPARC siRNA compared with those transfected with control siRNA. In an organotypic brain slice model, co-culture of glioma spheroids and rat brain slices showed that SPARC siRNA-transfected glioma cells failed to invade the surrounding normal brain tissue. In addition, intracerebral injection of glioma cells transfected with SPARC siRNA in nude mice resulted in the formation of a non-invasive tumor, whereas injection of cells transfected with control siRNA resulted in diffuse invasive tumors. Since SPARC was exclusively expressed in the invasive zone of the tumor margin and the area surrounding tumor necrosis, we investigated the relationship between SPARC expression and hypoxic stress. SPARC expression was upregulated under hypoxic stress of 1% oxygen concentration in glioma cells. Silencing hypoxia-inducible factor-1alpha with siRNA reduced the overexpression of SPARC induced under hypoxic conditions. These results suggest that SPARC plays an essential role in the invasive activity of human glioma cells, under hypoxic conditions. Downregulation of SPARC may be a novel anti-invasion therapeutic strategy for malignant gliomas.

Extratumoral Macrophages Promote Tumor and Vascular Growth in an Orthotopic Rat Prostate Tumor Model

Tumor-associated macrophages are involved in angiogenesis and tumor progression, but their role and specific site of action in prostate cancer remain unknown. To explore this, Dunning R-3327 AT-1 rat prostate tumor cells were injected into the prostate of syngenic and immunocompetent Copenhagen rats and analyzed at different time points for vascular proliferation and macrophage density. Endothelial proliferation increased with tumor size both in the tumor and importantly also in the extratumoral normal prostate tissue. Macrophages accumulated in the tumor and in the extratumoral normal prostate tissue and were most abundant in the invasive zone. Moreover, only extratumoral macrophages showed strong positive associations with tumor size and extratumoral vascular proliferation. Treatment with clodronate-encapsulated liposomes reduced the monocyte/macrophage infiltration and resulted in a significant inhibition of tumor growth. This was accompanied by a suppressed proliferation in microvessels and in the extratumoral prostate tissue also in arterioles and venules. The AT-1 tumors produced, as examined by RT2 Profiler PCR arrays, numerous factors promoting monocyte recruitment, angiogenesis, and tissue remodeling. Several, namely, chemokine (C-C) ligand 2, fibroblast growth factor 2, matrix metalloproteinase 9, interleukin 1β, interferon γ, and transforming growth factor β, were highly upregulated by the tumor in vivo compared with tumor cells in vitro, suggesting macrophages as a plausible source. In conclusion, we here show the importance of extratumoral monocytes/macrophages for prostate tumor growth, angiogenesis, and extratumoral arteriogenesis. Our findings identify tumor-associated macrophages and several chemotactic and angiogenic factors as potential targets for prostate cancer therapy.

Combined anti‐PDGFRα and PDGFRβ targeting in non‐small cell lung cancer

Activation of the platelet-derived growth factor (PDGF)-receptors is critically involved into various stromal cell functions including recruitment of stromal cells and vascular endothelial growth factor (VEGF) induction in tumor and perivascular cells. To evaluate the effects of combined PDGFRalpha and -beta inhibition in a non-small cell lung cancer model, we stably transfected A549 lung cancer cells with the PDGF-A mutant PDGF-0. PDGF-0 has been generated by substituting amino acids in the binding region of PDGF-A with the corresponding VEGF-A region, leading to a decreased receptor-binding affinity and activation. Compared with control vector transfected cells, transfection with PDGF-0 had no impact on monolayer growth and apoptosis in vitro, but significantly impaired the number of colony formation in soft agar. After subcutaneous injections, all mice developed tumors within 5 days. While control vector transfected A549 cells were characterized by constant tumor growth, PDGF-0 transfected A549 revealed a reduced tumor mass (p < 0.001) with no further growth beyond 14 days (2 months observation time) and complete regressions in 7 of 13 cases. Immunohistochemical analyses revealed that PDGF-0 transfected tumors demonstrated decreased recruitment of periendothelial cells, while the tumor invasion zone was similar to control vector transfectants. Similarly, conditioned medium from PDGF-0 transfected cells induced significantly less migration of smooth muscle cells and fibroblasts in vitro. Interestingly, in PDGF-0 transfectants, neither total vessel count nor VEGF expression were significantly altered. These studies demonstrate that combined inhibition of PDGFRalpha and -beta results in markedly decreased tumor growth in vivo because of impaired recruitment of periendothelial cells.

Use of tick surveys and serosurveys to evaluate pet dogs as a sentinel species for emerging Lyme disease

To evaluate dogs as a sentinel species for emergence of Lyme disease in a region undergoing invasion by Ixodes scapularis. 353 serum samples and 78 ticks obtained from dogs brought to 18 veterinary clinics located in the lower peninsula of Michigan from July 15, 2005, through August 15, 2005. Serum samples were evaluated for specific antibodies against Borrelia burgdorferi by use of 3 serologic assays. Ticks from dogs were subjected to PCR assays for detection of pathogens. Of 353 serum samples from dogs in 18 counties in 2005, only 2 (0.6%) contained western blot analysis-confirmed antibodies against B burgdorferi. Ten of 13 dogs with I scapularis were from clinics within or immediately adjacent to the known tick invasion zone. Six of 18 I scapularis and 12 of 60 noncompetent vector ticks were infected with B burgdorferi. No ticks were infected with Anaplasma phagocytophilum, and 3 were infected with Babesia spp. Serosurvey in dogs was found to be ineffective in tracking early invasion dynamics of I scapularis in this area. Tick chemoprophylaxis likely reduces serosurvey sensitivity in dogs. Ticks infected with B burgdorferi were more common and widely dispersed than seropositive dogs. In areas of low tick density, use of dogs as a source of ticks is preferable to serosurvey for surveillance of emerging Lyme disease. By retaining ticks from dogs for identification and pathogen testing, veterinarians can play an important role in early detection in areas with increasing risk of Lyme disease.

Multiple roles for cytokinin receptors and cross-talk of signaling pathways

Cytokinin receptors (CRs) are hybrid-type histidine kinases, membrane proteins with a cytokinin-binding extracellular domain. CRs initiate and propagate cytokinin signaling by means of phosphorylation and phosphotransfer to downstream proteins. In legumes, some members of the CR multigenic family are essential for nodulation. In two recent works, we investigated the involvement of two new CRs, MsHK1 from Medicago sativa, and LaHK1 from Lupinus albus, in nodule morphogenesis, senescence and stress response. LaHK1 expression increased during the first stages of lupin nodule development, while MsHK1 expression was localized in the meristem and the invasion zone of alfalfa nodules pointing to a role for CRs in nodule cell proliferation and differentiation. Both CRs were also induced during nodule senescence. MsHK1 expression increased under osmotic stress and both genes were induced following dark stress, indicating that CRs are also likely to play a significant role in the response to stress. We propose multiple roles for CRs which, when analyzed jointly with recent results from other authors, suggest coordinated cross-talk of different signaling systems.Addendum to: Coba de la Peña T, Cárcamo CB, Almonacid L, Zaballos A, Lucas MM, Balomenos D, Pueyo JJ. A salt stress-responsive cytokinin receptor homologue isolated from Medicago sativa nodules. Planta 2008; 227:769-79. and Coba de la Peña T, Cárcamo CB, Almonacid L, Zaballos A, Lucas MM, Balomenos D, Pueyo JJ. A cytokinin receptor homologue is induced during root nodule organogenesis and senescence in Lupinus albus L. Plant Physiol Biochem 2008; 46:219-25.

Structural and functional characterization of human Iba proteins

Iba2 is a homolog of ionized calcium-binding adapter molecule 1 (Iba1), a 17-kDa protein that binds and cross-links filamentous actin (F-actin) and localizes to membrane ruffles and phagocytic cups. Here, we present the crystal structure of human Iba2 and its homodimerization properties, F-actin cross-linking activity, cellular localization and recruitment upon bacterial invasion in comparison with Iba1. The Iba2 structure comprises two central EF-hand motifs lacking bound Ca2+. Iba2 crystallized as a homodimer stabilized by a disulfide bridge and zinc ions. Analytical ultracentrifugation revealed a different mode of dimerization under reducing conditions that was independent of Ca2+. Furthermore, no binding of Ca2+ up to 0.1 mM was detected by equilibrium dialysis. Correspondingly, Iba EF-hand motifs lack residues essential for strong Ca2+ coordination. Sedimentation experiments and microscopy detected pronounced, indistinguishable F-actin binding and cross-linking activity of Iba1 and Iba2 with induction of F-actin bundles. Fluorescent Iba fusion proteins were expressed in HeLa cells and co-localized with F-actin. Iba1 was recruited into cellular projections to a larger extent than Iba2. Additionally, we studied Iba recruitment in a Shigella invasion model that induces cytoskeletal rearrangements. Both proteins were recruited into the bacterial invasion zone and Iba1 was again concentrated slightly higher in the cellular extensions.

Computation of Triaxial Induction Logging Tools in Layered Anisotropic Dipping Formations

In order to interpret the logging data from triaxial induction tools, inversion technology has been adopted. To make the inversion process reasonably fast, a fast forward method must be developed. Numerical methods, such as the finite element method and finite difference method, are flexible but slow for inversion purposes. In this paper, an analytic method is developed to simulate induction tools in deviated wells drilled in anisotropic formations. This method can be applied to the triaxial induction tools with transmitting and receiving coils oriented in three mutually perpendicular directions. The axis of the tool may intercept a formation with dip, azimuthal, and orientation angles. Formulations of the electromagnetic fields generated by these three transmitting coils are derived. The derivation uses the coefficient propagator method with the assumption of negligible borehole effect and invasion zones. This method overcomes the problem of numerical overflow without compromising the accuracy of the solution. Because the new induction tool has three transmitting and three receiving coils, a total of nine logs are obtained at each logging depth compared with one or two logs in regular induction or logging while drilling tools.

A salt stress-responsive cytokinin receptor homologue isolated from Medicago sativa nodules

A new cytokinin receptor homologue, MsHK1, was isolated from Medicago sativa root nodules. MsHK1 expression was induced in alfalfa seedlings by exogenous application of the cytokinin trans-zeatin. Transcript accumulation was detected in different plant organs. MsHK1 expression was induced by salt stress in alfalfa roots, leaves and nodules, and transcript accumulation in the vascular bundles pointed to a putative role in osmosensing for MsHK1 and/or other close cytokinin receptor homologues. Expression in the meristem and the invasion zone of the nodule suggest a role for cytokinin receptors in cytokinin sensing during nodule cell division and differentiation.

Dynamic Modeling of Invasion Damage and Impact on Production in Horizontal Wells

Summary We present a novel approach that combines dynamic reservoir simulations and special core tests to model the extent of invasive damage and its impact on flowback during production. A radially adaptive 3D microsimulator is used to estimate the extent and impact of filtrate invasion on near-wellbore saturation and reservoir pressure. Time-varying reservoir exposure is used to simulate the acts of drilling, tripping, completions, and workovers. Extremely fine, core-scale grids are used to capture saturation and pressure in the invasion zone. Special core tests using a specially designed core holder are conducted on the subject reservoir core. Test results are interpreted to obtain an estimate of endpoint relative permeabilities, dynamic mudcake effect on filtrate loss, and impact of solids invasion on return permeability. The saturation and pressure profiles from this model are then used as initial conditions in a sector-scale simulator to model flowback effects. Absolute-permeability damage is modeled using the core-test results as an incremental and hyperbolically recovering effect during flowback simulations. A near-wellbore fine-grid overlay is used to capture the near-wellbore effects from the microsimulator results. Several sensitivities, including initial reservoir pressure, degree of overbalance and drawdown, heterogeneity, anisotropy, and mudcake effect, are examined. Equivalent skin factors that vary with time and depth are developed to enable comparison with full-field simulations. A horizontal-well example is used to illustrate the results of the study. Results illustrate the stark and often underappreciated effects of invasive damage on flowback and, therefore, on production performance. The methods described in this work can be used in reservoir-specific studies to quantify formation damage and aid in the selection of mud types, drilling techniques, and remediation methods required to improve performance. It is hoped that this work bridges the typically empirical damage-characterization methods and dynamic reservoir simulations.

Zoonotic Pathogens inIxodes scapularis, Michigan

Zoonotic Pathogens in<i>Ixodes scapularis</i>, Michigan