Stability of Nanometer-Thick Layered Gallium Chalcogenides and Improvements via Hydrogen Passivation

The gallium monochalcogenides family, comprising gallium sulfide (GaS), gallium selenide (GaSe), and gallium telluride (GaTe), is capturing attention for its applications in energy storage and production, catalysis, photonics, and optoelectronics. This interest originates from their properties, which include an optical bandgap larger than those of most common transition metal dichalcogenides, efficient light absorption, and significant carrier mobility. For any application, stability to air exposure is a fundamental requirement. Here, we perform a comparative study of the stability of layered GaS, GaSe, and GaTe nanometer-thick films down to a few layers with the goal of identifying the most suitable Ga chalcogenide for future integration in photonic and optoelectronic devices. Our study unveils a trend of decreasing air stability from sulfide to selenide and finally to telluride. Furthermore, we demonstrate a hydrogen passivation process to prevent the oxidation of GaSe with a higher feasibility and durability than other state-of-the-art passivation methods proposed in the literature.

Directional Scattering Switching from an All-Dielectric Phase Change Metasurface

All-dielectric metasurfaces are a blooming field with a wide range of new applications spanning from enhanced imaging to structural color, holography, planar sensors, and directionality scattering. These devices are nanopatterned structures of sub-wavelength dimensions whose optical behavior (absorption, reflection, and transmission) is determined by the dielectric composition, dimensions, and environment. However, the functionality of these metasurfaces is fixed at the fabrication step by the geometry and optical properties of the dielectric materials, limiting their potential as active reconfigurable devices. Herein, a reconfigurable all-dielectric metasurface based on two high refractive index (HRI) materials like silicon (Si) and the phase-change chalcogenide antimony triselenide (Sb₂Se₃) for the control of scattered light is proposed. It consists of a 2D array of Si-Sb₂Se₃-Si sandwich disks embedded in a SiO₂ matrix. The tunability of the device is provided through the amorphous-to-crystalline transition of Sb₂Se₃. We demonstrate that in the Sb₂Se₃ amorphous state, all the light can be transmitted, as it is verified using the zero-backward condition, while in the crystalline phase most of the light is reflected due to a resonance whose origin is the contribution of the electric (ED) and magnetic (MD) dipoles and the anapole (AP) of the nanodisks. By this configuration, a contrast in transmission (ΔT) of 0.81 at a wavelength of 980 nm by governing the phase of Sb₂Se₃ can be achieved.

Plasmonic hot-electron reconfigurable photodetector based on phase-change material Sb2S3

Hot-carrier based photodetectors and enhanced by surface plasmons (SPs) hot-electron injection into semiconductors, are drawing significant attention. This photodetecting strategy yields to narrowband photoresponse while enabling photodetection at sub-bandgap energies of the semiconductor materials. In this work, we analyze the design of a reconfigurable photodetector based on a metal-semiconductor (MS) configuration with interdigitated dual-comb Au electrodes deposited on the semiconducting Sb₂S₃ phase-change material. The reconfigurability of the device relies on the changes of refractive index between the amorphous and crystalline phases of Sb₂S₃ that entail a modulation of the properties of the SPs generated at the dual-comb Au electrodes. An exhaustive numerical study has been realized on the Au grating parameters formed by the dual-comb electrodes, and on the SP order with the purpose of optimizing the absorption of the device, and thus, the responsivity of the photodetector. The optimized photodetector layout proposed here enables tunable narrowband photodetection from the O telecom band (λ = 1310 nm) to the C telecom band (λ = 1550 nm).

Layered gallium sulfide optical properties from monolayer to CVD crystalline thin films

Interest in layered van der Waals semiconductor gallium monosulfide (GaS) is growing rapidly because of its wide band gap value between those of two-dimensional transition metal dichalcogenides and of insulating layered materials such as hexagonal boron nitride. For the design of envisaged optoelectronic, photocatalytic and photonic applications of GaS, the knowledge of its dielectric function is fundamental. Here we present a combined theoretical and experimental investigation of the dielectric function of crystalline 2H-GaS from monolayer to bulk. Spectroscopic imaging ellipsometry with micron resolution measurements are corroborated by first principle calculations of the electronic structure and dielectric function. We further demonstrate and validate the applicability of the established dielectric function to the analysis of the optical response of c-axis oriented GaS layers grown by chemical vapor deposition (CVD). These optical results can guide the design of novel, to our knowledge, optoelectronic and photonic devices based on low-dimensional GaS.

Interlaboratory study on Sb2S3 interplay between structure, dielectric function, and amorphous-to-crystalline phase change for photonics

Antimony sulfide, Sb₂S₃, is interesting as the phase-change material for applications requiring high transmission from the visible to telecom wavelengths, with its band gap tunable from 2.2 to 1.6 eV, depending on the amorphous and crystalline phase. Here we present results from an interlaboratory study on the interplay between the structural change and resulting optical contrast during the amorphous-to-crystalline transformation triggered both thermally and optically. By statistical analysis of Raman and ellipsometric spectroscopic data, we have identified two regimes of crystallization, namely 250°C ≤ T < 300°C, resulting in Type-I spherulitic crystallization yielding an optical contrast Δn ∼ 0.4, and 300 ≤ T < 350°C, yielding Type-II crystallization bended spherulitic structure with different dielectric function and optical contrast Δn ∼ 0.2 below 1.5 eV. Based on our findings, applications of on-chip reconfigurable nanophotonic phase modulators and of a reconfigurable high-refractive-index core/phase-change shell nanoantenna are designed and proposed.

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Study of the dielectric function of amorphous and crystalline Sb2S3 phase change material

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Identification of two crystallization regimes for the phase change of Sb2S3

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Design of Sb2S3 on-chip reconfigurable photonic phase modulator

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Design of reconfigurable high-refractive index core/phase-change shell nanoantenna

Exploring the Thickness-Dependence of the Properties of Layered Gallium Sulfide

Group III layered monochalcogenide gallium sulfide, GaS, is one of the latest additions to the two-dimensional (2D) materials family, and of particular interest for visible-UV optoelectronic applications due to its wide bandgap energy in the range 2.35–3.05 eV going from bulk to monolayer. Interestingly, when going to the few-layer regime, changes in the electronic structure occur, resulting in a change in the properties of the material. Therefore, a systematic study on the thickness dependence of the different properties of GaS is needed. Here, we analyze mechanically exfoliated GaS layers transferred to glass substrates. Specifically, we report the dependence of the Raman spectra, photoluminescence, optical transmittance, resistivity, and work function on the thickness of GaS. Those findings can be used as guidance in designing devices based on GaS.

CDDA: extension and analysis of the discrete dipole approximation for chiral systems

Discrete dipole approximation (DDA) is a computational method broadly used to solve light scattering problems. In this work, we propose an extension of DDA that we call Chiral-DDA (CDDA), to study light-chiral matter interactions with the capability of describing the underlying physics behind. Here, CDDA is used to solve and analyze the interaction of a nanoantenna (either metallic or dielectric) with a chiral molecule located in its near field at different positions. Our method allowed to relate near field interactions with far field spectral response of the system, elucidating the role that the nanoantenna electric and magnetic polarizabilities play in the coupling with a chiral molecule. In general, this is not straightforward with other methods. We believe that CDDA has the potential to help researchers revealing some of the still unclear mechanisms responsible for the chiral signal enhancements induced by nanoantennas.

Gallium Plasmonic Nanoantennas Unveiling Multiple Kinetics of Hydrogen Sensing, Storage, and Spillover

Hydrogen is the key element to accomplish a carbon-free based economy. Here, the first evidence of plasmonic gallium (Ga) nanoantennas is provided as nanoreactors supported on sapphire (α-Al₂ O₃ ) acting as direct plasmon-enhanced photocatalyst for hydrogen sensing, storage, and spillover. The role of plasmon-catalyzed electron transfer between hydrogen and plasmonic Ga nanoparticle in the activation of those processes is highlighted, as opposed to conventional refractive index-change-based sensing. This study reveals that, while temperature selectively operates those various processes, longitudinal (LO-LSPR) and transverse (TO-LSPR) localized surface plasmon resonances of supported Ga nanoparticles open selectivity of localized reaction pathways at specific sites corresponding to the electromagnetic hot-spots. Specifically, the TO-LSPR couples light into the surface dissociative adsorption of hydrogen and formation of hydrides, whereas the LO-LSPR activates heterogeneous reactions at the interface with the support, that is, hydrogen spillover into α-Al₂ O₃ and reverse-oxygen spillover from α-Al₂ O_3. This Ga-based plasmon-catalytic platform expands the application of supported plasmon-catalysis to hydrogen technologies, including reversible fast hydrogen sensing in a timescale of a few seconds with a limit of detection as low as 5 ppm and in a broad temperature range from room-temperature up to 600 °C while remaining stable and reusable over an extended period of time.

Non-Absorbing Dielectric Materials for Surface-Enhanced Spectroscopies and Chiral Sensing in the UV

Low-loss dielectric nanomaterials are being extensively studied as novel platforms for enhanced light-matter interactions. Dielectric materials are more versatile than metals when nanostructured as they are able to generate simultaneously electric- and magnetic-type resonances. This unique property gives rise to a wide gamut of new phenomena not observed in metal nanostructures such as directional scattering conditions or enhanced optical chirality density. Traditionally studied dielectrics such as Si, Ge or GaP have an operating range constrained to the infrared and/or the visible range. Tuning their resonances up to the UV, where many biological samples of interest exhibit their absorption bands, is not possible due to their increased optical losses via heat generation. Herein, we report a quantitative survey on the UV optical performance of 20 different dielectric nanostructured materials for UV surface light-matter interaction based applications. The near-field intensity and optical chirality density averaged over the surface of the nanoparticles together with the heat generation are studied as figures of merit for this comparative analysis.

Sustainable and Tunable Mg/MgO Plasmon-Catalytic Platform for the Grand Challenge of SF6 Environmental Remediation

Sulfur hexafluoride (SF₆) is one of the most harmful greenhouse gases producing environmental risks. Therefore, developing ways of degrading SF₆ without forming hazardous products is increasingly important. Herein, we demonstrate for the first time the plasmon-catalytic heterogeneous degradation of SF₆ into nonhazardous MgF₂ and MgSO₄ products by nontoxic and sustainable plasmonic magnesium/magnesium oxide (Mg/MgO) nanoparticles, which are also effective as a plasmon-enhanced SF₆ chemometric sensor. The main product depends on the excitation wavelength; when the localized surface plasmon resonance (LSPR) is in the ultraviolet, then MgF₂ forms, while visible light LSPR results in MgSO₄. Furthermore, Mg/MgO platforms can be regenerated in few seconds by hydrogen plasma treatment and can be reused in a new cycle of air purification. Therefore, this research first demonstrates effectiveness of Mg/MgO plasmon-catalysis enabling environmental remediation with the concurrent functionalities of monitoring, degrading, and detecting sulfur and fluorine gases in the atmosphere.

Life History Traits and Predatory Performance of Belostoma anurum (Hemiptera: Belostomatidae), a Biological Control Agent of Disease Vector Mosquitoes

Understanding the life cycle and dietary requirements of laboratory-reared insects is critical for optimizing resources (including time) and can provide more reliable ecological basis for using such biological control agents in realistic programs. Here, we evaluated the complete development and the predatory abilities of Belostoma anurum (Herrich-Schäffer, 1848) (Hemiptera: Belostomatidae), an aquatic predator widely distributed in Neotropical region, when reared at different diets. We firstly investigated the predatory performance of B. anurum nymphs upon mosquito larvae (i.e., larvae of Aedes aegypti (Linnaeus, 1758) or Culex sp. (Diptera: Culicidae)) and, second, whether the immature diets (i.e., arthropod-based diet (mosquito larvae and adults of Notonectidae) or vertebrate (fish larvae)-based diet) affect the predatory behavior of B. anurum adults. The B. anurum egg-to-adult developmental time was 85.1 days in an arthropod-based diet. However, when a fish-based diet was offered after nymphs reached 3rd instar, we recorded up to 50% reductions on the B. anurum developmental time. Interestingly, B. anurum adults could live more than 1 year under laboratory conditions, independently of the immature diet regime. Furthermore, the fish diet-experienced B. anurum adults spent less time feeding on fish larvae when compared with adults that never experienced this type of diet. Predatory results revealed that 2nd instar B. anurum were more efficient to catch and consume larvae of A. aegypti than of Culex sp. Collectively, our findings show that B. anurum is long-lived aquatic predators, and demonstrate the impacts of dietary regime on the life history traits and predatory performance of these insects.

Plasmon-Enhanced Catalysis: Distinguishing Thermal and Nonthermal Effects

In plasmon-enhanced heterogeneous catalysis, illumination accelerates reaction rates by generating hot carriers and hot surfaces in the constituent nanostructured metals. In order to understand how photogenerated carriers enhance the nonthermal reaction rate, the effects of photothermal heating and thermal gradients in the catalyst bed must be confidently and quantitatively characterized. This is a challenging task considering the conflating effects of light absorption, heat transport, and reaction energetics. Here, we introduce a methodology to distinguish the thermal and nonthermal contributions from plasmon-enhanced catalysts, demonstrated by illuminated rhodium nanoparticles on oxide supports to catalyze the CO₂ methanation reaction. By simultaneously measuring the total reaction rate and the temperature gradient of the catalyst bed, the effective thermal reaction rate may be extracted. The residual nonthermal rate of the plasmon-enhanced reaction is found to grow with a superlinear dependence on illumination intensity, and its apparent quantum efficiency reaches ∼46% on a Rh/TiO₂ catalyst at a surface temperature of 350 °C. Heat and light are shown to work synergistically in these reactions: the higher the temperature, the higher the overall nonthermal efficiency in plasmon-enhanced catalysis.

The UV Plasmonic Behavior of Distorted Rhodium Nanocubes

For applications of surface-enhanced spectroscopy and photocatalysis, the ultraviolet (UV) plasmonic behavior and charge distribution within rhodium nanocubes is explored by a detailed numerical analysis. The strongest plasmonic hot-spots and charge concentrations are located at the corners and edges of the nanocubes, exactly where they are the most spectroscopically and catalytically active. Because intense catalytic activity at corners and edges will reshape these nanoparticles, distortions of the cubical shape, including surface concavity, surface convexity, and rounded corners and edges, are also explored to quantify how significantly these distortions deteriorate their plasmonic and photocatalytic properties. The fact that the highest fields and highest carrier concentrations occur in the corners and edges of Rh nanocubes (NCs) confirms their tremendous potential for plasmon-enhanced spectroscopy and catalysis. It is shown that this opportunity is fortuitously enhanced by the fact that even higher field and charge concentrations reside at the interface between the metal nanoparticle and a dielectric or semiconductor support, precisely where the most chemically active sites are located.

Polarimetric response of magnetodielectric core-shell nanoparticles: an analysis of scattering directionality and sensing

The influence of increasing the core size of Ag-Si core-shell nanoparticles has been investigated by using the values of the linear polarization degree at a right-angle scattering configuration, [Formula: see text]. Changes in dipolar resonances and scattering directionality conditions as a function of the core radius (R int) for a fixed shell size ([Formula: see text] nm) have been analysed. An empirical formula to obtain the ratio [Formula: see text] by monitoring the influence of the magnetic dipolar resonance in [Formula: see text] has been found. The effect of the refractive index of the surrounding medium, m med, in the zero backward and almost-zero forward scattering conditions has also been studied. We have weighed up the sensitivity of [Formula: see text] to m med. It has been demonstrated that multipolar contributions strongly influence [Formula: see text]. This influence can be used as a fast m med estimate. In all cases, the results show that the bigger the cores, the higher the sensitivity to m med.

Size-tunable rhodium nanostructures for wavelength-tunable ultraviolet plasmonics

Polydisperse rhodium nanoparticles have recently shown promise for ultraviolet (UV) plasmonics, but controlling the size and morphology of metal nanoparticles is essential for tuning surface plasmon resonances. Here we report the use of slow-injection polyol methods to synthesize monodisperse Rh nanocubes with unprecedentedly large sizes and slightly concave faces. The associated local surface plasmon resonances (LSPRs) red-shifted with increasing sizes in the UV region from deep UV to around 400 nm, consistent with numerical simulations. UV illumination of p-aminothiophenol attached to the Rh nanocubes generated surface-enhanced Raman spectra and accelerated photo-decomposition, and these enhancements were largest for nanocubes whose LSPR was resonant with the UV laser. The lack of a native oxide coating, the precise control of nanocube size and morphology demonstrated here, and the ability to tune the surface plasmon resonance from the deep UV to near UV spectral region, make rhodium a compelling choice for UV plasmonic applications.

In vitroantiviral activity ofPhyllanthus orbicularisextracts against herpes simplex virus type 1

The antiviral activity of butanol- and acetic acid-soluble fractions, prepared from the leaves and stems of Phyllanthus orbicularis H.B.K., has been investigated against acyclovir-sensitive or -resistant herpes simplex virus type 1 (HSV-1) strains, using human foreskin fibroblast (HFF) and green ape kidney (Vero) cell lines. Both fractions showed antiviral selectivity indexes (SI) from 10.3 to 22.8, while their extracellular virucidal activities reached SI values ranging from 371 to 1,040. Time-addition experiments suggested that the active compounds present in the studied fractions acted on early steps of the virus replication cycle.

Safety and preliminary immunogenicity of the recombinant outer membrane protein P64k of Neisseria meningitidis in human volunteers

P64k is a meningococcal protein from Neisseria meningitidis that has been obtained by recombinant DNA technology. Recombinant P64k has been extensively characterized by physicochemical and immunological methods. Lately this protein has been found to act as a versatile immunological carrier for weak antigens in mice. In the present work, a Phase I clinical trial was carried out in healthy volunteers who received three inoculations of either placebo or recombinant P64k (20 or 50 microg). No severe adverse events occurred during the trial. Only mild adverse events in ten volunteers were observed. At 1 month after the third dose, 15 out of 18 volunteers (83.3%) who received the recombinant antigen had a P64k-specific antibody titre > or =1:100, as detected by ELISA. A fourth dose, given 9 months after the third one, elicited a potent booster immune response in P64k vaccinees. Accordingly, these P64k formulations were considered safe and immunogenic in healthy human volunteers.

Impairment of H+-K+-ATPase-dependent proton transport and inhibition of gastric acid secretion by ethanol

Ethanol (1-20% vol/vol) caused a dose-dependent reduction in the basal rate of acid formation in isolated rabbit gastric glands with a calculated EC(50) value of 4.5 +/- 0.2%. Ethanol also reduced ATP levels in isolated gastric glands and in cultured parietal cells (EC(50): 8.8 +/- 0.4% and 8.5 +/- 0.2%, respectively) and decreased both basal and forskolin-stimulated cAMP levels. In studies carried out in gastric gland microsomes, ethanol inhibited the hydrolytic activity of H+-K+-ATPase(EC(50): 8.5 +/- 0.6%), increased passive proton permeability (EC(50): 7.9%), and reduced H+-K+-ATPase-dependent proton transport (EC(50): 3%). Our results show that the inhibition of gastric acid secretion observed at low concentrations of ethanol (< or =5%) is mainly caused by the specific impairment of H+-K+-ATPase-dependent proton transport across cell membranes rather than inhibition of the hydrolytic activity of H+-K+-ATPase, reduction in the cellular content of ATP, or increase in the passive permeability of membranes to protons, although these changes, in combination, must be relevant at concentrations of ethanol > or =7%.

Neisseria gonorrhoeae resistant to ciprofloxacin: first report in Cuba

BACKGROUND AND OBJECTIVES

The Cuban Ministry of Public Health plans to implement the syndromic approach to sexually transmitted diseases in persons with urethral or vaginal syndrome in Cuba using 500 mg ciprofloxacin as therapy. Although the emergence of clinical isolates of Neisseria gonorrhoeae with decreased susceptibility to ciprofloxacin have been sporadically detected in Cuba, there has been no report of isolates that exhibited significant resistance to this drug. This is the first report of the isolation of a N gonorrhoeae strain resistant to ciprofloxacin in Cuba.

STUDY DESIGN

Case report.

CONCLUSIONS

This case emphasizes the need for awareness regarding the potential emergence of a clinically significant resistance of N gonorrhoeae in Cuba. There is a need for continued antimicrobial susceptibility surveillance of Cuban isolates to ciprofloxacin and other fluoroquinolones.

Characterization of Neisseria gonorrhoeae strains isolated from patients with conjunctivitis

The conjunctivitis produced by Neisseria gonorrhoeae is the less frequently reported clinical form of gonococcal infection. We aim to phenotypically characterize N. gonorrhoeae isolated from conjunctivae sites. A total of six cases of this disease were notified in the Camagüey province, Cuba. All the strains isolated were penicillin-producing, showed the serogroup WI and exhibited the same antimicrobial susceptibility pattern and plasmid profile (2.6-3. 2-24.5). The results contribute to the characterization of N. gonorrhoeae strains circulating in our environment.

Sulfonylurea effects on acid and pepsinogen secretion in isolated rabbit gastric glands

The influence of different sulfonylureas on the rate of acid and pepsinogen secretion was studied in isolated rabbit gastric glands. Neither tolbutamide (10-500 microM), chlorpropamide (10-500 microM), glibenclamide (1-50 microM) nor glipizide (1-50 microM) exerted a secretory effect. In contrast, gliquidone caused a marked and dose-dependent stimulation of acid production in gastric glands incubated under basal conditions and potentiated the stimulatory effect of both histamine and carbachol. Gliquidone also increased the rate of pepsinogen release in gastric glands incubated either under basal conditions or in the presence of cholecystokinin-octapeptide or isoproterenol. The secretory effects of gliquidone were associated with a significant increase in the glandular content of cyclic AMP, caused by a competitive inhibition of low-Km cyclic AMP phosphodiesterase. Our results indicate that, among the assayed sulfonylureas, only gliquidone, in the micromolar range, stimulates acid and pepsinogen secretion through a cyclic AMP-dependent mechanism.

Nitric oxide in different types of hypertension during pregnancy

1. Serum nitric oxide (NO) levels (determined by its products of oxidation) were assessed in non-pregnant women, normal pregnant women and patients suffering from mild pre-eclampsia (MPE), severe pre-eclampsia (SPE), chronic hypertension (CHT) and CHT with pre-eclampsia (CHT + PE). The levels of NO products were significantly reduced during pregnancy in MPE (P < 0.001), CHT + PE (P < 0.01) and SPE (P < 0.05). Significant reductions of NO products were also observed in puerperium (P < 0.001) in all groups except CHT + PE (P < 0.05). 2. In normal pregnancy, three events were related to NO levels: (1) negative correlations were found between the levels of nitrite (r = -0.73, P = 0.0003), nitrate (r = -0.53, P = 0.017) and the number of weeks of gestation; (2) in the caesarean section group, the levels of NO at puerperium were significantly lower (P < 0.05) than those during pregnancy; and (3) there was a significant reduction in NO levels in the pregnant women carrying male fetuses as compared with female fetuses (P < 0.05). 3. In SPE, the patients with a family history of hypertension had lower levels of NO compared with the patients without such a history (P < 0.05). 4. A negative correlation was observed between systolic blood pressure, diastolic blood pressure and NO levels in MPE (r = -0.62, P = 0.013 and r = -0.68, P = 0.0049 respectively) and SPE (r = -0.72, P = 0.004 and r = -0.53, P = 0.037 respectively). 5. In SPE, positive correlations were observed between platelet count and nitrite (r = 0.67, P = 0.006) and nitrate levels (r = 0.56, P = 0.028). 6. In MPE, patients with anti-hypertensive treatment showed significantly (P < 0.05) higher levels of NO compared with the non-treated patients. 7. NO may be important in the physiopathology of hypertension during pregnancy, although several factors may affect its levels.

Fatal human pulmonary infection caused by an Angiostrongylus-like nematode

An immunocompetent man developed malaise, fever, progressive weight loss, eosinophilia, and transient pulmonary infiltrates that responded to steroid treatment but recurred after its discontinuation. Examinations of feces, bronchoalveolar lavage fluid, and pulmonary tissue obtained during a 50-day period of hospitalization yielded negative results. When a new bronchoalveolar lavage sample and a new pulmonary biopsy specimen showed nematode larvae and adult worms, treatment with thiabendazole was started. However, therapy with this agent and then with mebendazole had no impact on the patient's downhill course, which ended in respiratory distress and death. Autopsy documented an overwhelming pulmonary infection with a metastrongylid nematode resembling a species of Angiostrongylus. Histologic study revealed features of necrotizing angiitis closely mimicking those of Wegener's granulomatosis. To our knowledge, this is the first reported instance of patent metastrongylid parasitism of the human pulmonary arteries with necrotizing angiitis caused by a reaction to the parasite and/or its metabolic products.