Factors limiting quantitative phase retrieval in atomic-resolution differential phase contrast scanning transmission electron microscopy using a segmented detector.

Quantitative differential phase contrast imaging of materials in atomic-resolution scanning transmission electron microscopy using segmented detectors is limited by various factors, including coherent and incoherent aberrations, detector positioning and uniformity, and scan-distortion. By comparing experimental case studies of monolayer and few-layer graphene with image simulations, we explore which parameters require the most precise characterisation for reliable and quantitative interpretation of the reconstructed phases. Coherent and incoherent lens aberrations are found to have the most significant impact. For images over a large field of view, the impact of noise and non-periodic boundary conditions are appreciable, but in this case study have less of an impact than artefacts introduced by beam deflections coupling to beam scanning (imperfect tilt-shift purity).

Accuracy and precision of thickness determination from position-averaged convergent beam electron diffraction patterns using a single-parameter metric.

Position-averaged convergent beam electron diffraction patterns are formed by averaging the transmission diffraction pattern while scanning an atomically-fine electron probe across a sample. Visual comparison between experimental and simulated patterns is increasingly being used for sample thickness determination. We explore automating the comparison via a simple sum square difference metric. The thickness determination is shown to be accurate (i.e. the best-guess deduced thickness generally concurs with the true thickness), though factors such as noise, mistilt and inelastic scattering reduce the precision (i.e. increase the uncertainty range). Notably, the precision tends to be higher for smaller probe-forming aperture angles.

Composition measurement in substitutionally disordered materials by atomic resolution energy dispersive X-ray spectroscopy in scanning transmission electron microscopy.

The increasing use of energy dispersive X-ray spectroscopy in atomic resolution scanning transmission electron microscopy invites the question of whether its success in precision composition determination at lower magnifications can be replicated in the atomic resolution regime. In this paper, we explore, through simulation, the prospects for composition measurement via the model system of AlxGa1-xAs, discussing the approximations used in the modelling, the variability in the signal due to changes in configuration at constant composition, and the ability to distinguish between different compositions. Results are presented in such a way that the number of X-ray counts, and thus the expected variation due to counting statistics, can be gauged for a range of operating conditions.

Low magnification differential phase contrast imaging of electric fields in crystals with fine electron probes.

To correlate atomistic structure with longer range electric field distribution within materials, it is necessary to use atomically fine electron probes and specimens in on-axis orientation. However, electric field mapping via low magnification differential phase contrast imaging under these conditions raises challenges: electron scattering tends to reduce the beam deflection due to the electric field strength from what simple models predict, and other effects, most notably crystal mistilt, can lead to asymmetric intensity redistribution in the diffraction pattern which is difficult to distinguish from that produced by long range electric fields. Using electron scattering simulations, we explore the effects of such factors on the reliable interpretation and measurement of electric field distributions. In addition to these limitations of principle, some limitations of practice when seeking to perform such measurements using segmented detector systems are also discussed.

Energy dispersive X-ray analysis on an absolute scale in scanning transmission electron microscopy.

We demonstrate absolute scale agreement between the number of X-ray counts in energy dispersive X-ray spectroscopy using an atomic-scale coherent electron probe and first-principles simulations. Scan-averaged spectra were collected across a range of thicknesses with precisely determined and controlled microscope parameters. Ionization cross-sections were calculated using the quantum excitation of phonons model, incorporating dynamical (multiple) electron scattering, which is seen to be important even for very thin specimens.

Genetic epidemiology of Sarcoptes scabiei (Acari: Sarcoptidae) in northern Australia.

Utilising three hypervariable microsatellite markers we have previously shown that scabies mites on people are genetically distinct from those on dogs in sympatric populations in northern Australia. This had important ramifications on the formulation of public health control policies. In contrast phylogenetic analyses using mitochondrial markers on scabies mites infecting multiple animal hosts elsewhere in the world could not differentiate any genetic variation between mite haplotype and host species. Here we further analyse the intra-specific relationship of Sarcoptes scabiei var. hominis with S. scabiei var. canis by using both mitochondrial DNA and an expanded nuclear microsatellite marker system. Phylogenetic studies using sequences from the mitochondrial genes coding for 16S rRNA and Cytochrome Oxidase subunit I demonstrated significant relationships between S. scabiei MtDNA haplotypes, host species and geographical location. Multi-locus genotyping using 15 microsatellite markers substantiated previous data that gene flow between scabies mite populations on human and dog hosts is extremely rare in northern Australia. These data clearly support our previous contention that control programs for human scabies in endemic areas with sympatric S. scabiei var. hominis and var. canis populations must focus on human-to-human transmission. The genetic division of dog and human derived scabies mites also has important implications in vaccine and diagnostic test development as well as the emergence and monitoring of drug resistance in S. scabiei in northern Australia.

Dermatophytosis in Vietnam.

Professor Taplin describes his experiments producing clinical lesions with 2 endemic dermatophytes encountered in Vietnam during the Vietnam War: the human-adapted Trichophyton raubitschekii, possibly a regional form of Trichophyton rubrum that was causing chronic tinea corporis in the Vietnamese, and a zoophilic Trichophyton mentagrophytes that caused highly inflammatory ringworm in the previously unexposed American soldiers. (This particular T mentagrophytes was also the fungus studied by Dr. Jones.).

Genetically distinct dog-derived and human-derived Sarcoptes scabiei in scabies-endemic communities in northern Australia.

Overcrowding is a significant factor contributing to endemic infection with Sarcoptes scabiei in human and animal populations. However, since scabies mites from different host species are indistinguishable morphologically, it is unclear whether people can be infected from scabies-infested animals. Molecular fingerprinting was done using three S. scabiei-specific single locus hypervariable microsatellite markers, with a combined total of 70 known alleles. Multilocus analysis of 712 scabies mites from human and dog hosts in Ohio, Panama and Aboriginal communities in northern Australia now shows that genotypes of dog-derived and human-derived scabies cluster by host species rather than by geographic location. Because of the apparent genetic separation between human scabies and dog scabies, control programs for human scabies in endemic areas do not require resources directed against zoonotic infection from dogs.

Age, renal perfusion and function in island-dwelling indigenous Kuna Amerinds of Panama.

BACKGROUND/AIMS: Among possible contributors to a progressive fall in renal perfusion and function with increasing age, some hypotheses have invoked the rise in blood pressure that occurs with age, and a high-protein diet typical of urban cultures. Kuna Amerinds residing in isolated islands off the Panamanian Coast have a very low protein intake and show no tendency for blood pressure to rise with age, thus providing an opportunity to test these hypotheses. METHODS: We measured renal plasma flow and glomerular filtration rate (PAH and inulin clearance) in 16 Kuna Indians ranging in age from 18 to 86 years (51 +/- 6 years) who have resided on Ailigandi, an isolated Panamanian island for all of their lives. Inulin and PAH were infused with a battery-driven pump for 60 min, and a metabolic clearance rate used to calculate inulin and PAH clearance. For comparison, we employed identical techniques in 29 residents of Boston, ranging in age from 19 to 79 years (52 +/- 4 years), all normotensive and free of disease or medication use. Twenty-four were Caucasian. RESULTS: The Bostonian controls showed the anticipated fall in PAH clearance with age (y = 806 - 4.9 x; r = -0.82; f = 38.0; p < 0.0001). Our hypothesis was that the absence of a blood pressure rise with age and the low protein intake would flatten the slope relating renal perfusion to Kuna age. Our finding was a numerically steeper slope relating age and renal plasma flow in the Kuna (y = 936 - 6.48x; r = -0.81; p < 0.001). Filtration fraction rose with age in both populations, and again the rise was steeper in the Kuna. GFR in the Kuna, on the other hand, was very much higher at any age (139 +/- 4 ml/min/1.73 m2) than in Bostonians (112 +/- 3 ml/min/1.73 m2; p < 0.001). CONCLUSION: The findings are not in accord with the hypothesis that age-related changes in renal perfusion and glomerular filtration rate reflect an important contribution from blood pressure rise and a high protein intake, typical of modern, urban life.

Isolation, amplification, and sequencing of human mitochondrial DNA obtained from human crab louse, Pthirus pubis (L.), blood meals.

The ability to identify individual human hosts based on analyses of blood recovered from the digestive tract of hematophagous arthropods has been a long-term pursuit in both medical and forensic entomology. Blood meal individualization techniques can bring important advancements to studies of vector-borne disease epidemiology. Forensically, these analyses may aid in assailant identification in violent crime cases where blood-feeding insects or their excreta are recovered from victims or at crime scenes. Successful isolation, amplification, and sequencing of human mitochondrial DNA obtained from adult human crab lice fed on human volunteers are reported. Adult lice were removed from recruited volunteers frequenting inner city health clinics. Live lice were killed by freezing and subsequently air dried at ambient temperature. A saliva sample was obtained from each volunteer and served as a DNA reference sample. Volunteers were afforded free, approved pediculosis treatment. Individual lice were subsequently processed using procedures developed for the extraction of mitochondrial DNA from human hair, teeth, and bone. The resulting DNA was amplified by the polymerase chain reaction and sequenced. Our results point to valuable avenues for future entomological research.

Treatment of HIV-related scabies with emphasis on the efficacy of ivermectin.

Since the mid-1980s, worldwide reports confirm that scabies in individuals infected with the human immunodeficiency virus (HIV) result in a wide range of-clinical manifestations which differ from those seen in immunocompetent patients. There is also general agreement that HIV-related scabies is more difficult to treat. Oral ivermectin has been shown in several countries to be a safe and effective therapy. In otherwise healthy persons, one dose of 200 microg/kg is usually curative. In HIV-related scabies, one treatment may be curative but repeated doses may be required. Crusted scabies in these individual requires a combination of oral ivermectin, total body treatments with 5% permethrin cream, and keratolytic agents to hasten removal of crusts.

Aging, acculturation, salt intake, and hypertension in the Kuna of Panama.

The indigenous Kuna who live on islands in the Panamanian Caribbean were among the first communities described with little age-related rise in blood pressure or hypertension. Our goals in this study were to ascertain whether isolated island-dwelling Kuna continue to show this pattern, whether migration to Panama City and its environs changed the patterns, and whether the island-dwelling Kuna have maintained their normal blood pressure levels despite partial acculturation, reflected in an increased salt intake. We enrolled 316 Kuna participants who ranged in age from 18 to 82 years. In 50, homogeneity was confirmed by documentation of an O+ blood group. In 92 island dwellers, diastolic hypertension was not identified and blood pressure levels were as low in volunteers over 60 years of age as in those between 20 and 30 years of age. In Panama City, conversely, hypertension prevalence was 10.7% and exceeded 45% in those over 60 years of age (P < .01), blood pressure levels were higher in the elderly, and there was a statistically significant positive relationship between age and blood pressure (P < .01). In Kuna Nega, a Panama City suburb designed to maintain a traditional Kuna lifestyle but with access to the city, all findings were intermediate. Sodium intake and excretion assessed in 50 island-dwelling Kuna averaged 135 +/- 15 mEq/g creatinine per 24 hours, exceeding substantially other communities free of hypertension and an age-related rise in blood pressure. Despite partial acculturation, the island-dwelling Kuna Indians are protected from hypertension and thus provide an attractive population for examining alternative mechanisms.

The treatment of scabies with ivermectin.

BACKGROUND: Ivermectin is an anthelmintic agent that has been a safe, effective treatment for onchocerciasis (river blindness) when given in a single oral dose of 150 to 200 micrograms per kilogram of body weight. Anecdotal reports of improvement in patients who suffered from infestation with the mite Sarcoptes scabiei suggest that the ectoparasitic disease scabies might be treated with ivermectin. METHODS: We conducted an open-label study in which ivermectin was administered in a single oral dose of 200 micrograms per kilogram to 11 otherwise healthy patients with scabies and to 11 patients with scabies who were also infected with the human immunodeficiency virus (HIV), 7 of whom had the acquired immunodeficiency syndrome. All patients received a full physical and dermatologic examination; scrapings from the skin of all patients tested positive for scabies. Patients were reexamined two and four weeks after treatment, when the scrapings for scabies were repeated. The patients used no other scabicides during the 30 days before ivermectin treatment or during the 4-week study period. RESULTS: None of the 11 otherwise healthy patients had evidence of scabies four weeks after a single dose of ivermectin. Of the 11 HIV-infected patients, 2 had < or = 10 scabies lesions before treatment, 3 had 11 to 49 lesions, 4 had > or = 50 lesions, and 2 had heavily crusted skin lesions. In eight of the patients the scabies was cured after a single dose of ivermectin. Two patients received a second dose two weeks after the first. Ten of the 11 patients with HIV infection (91 percent) had no evidence of scabies four weeks after their first treatment with ivermectin. CONCLUSIONS: The anthelmintic agent ivermectin, given in a single oral dose, is an effective treatment for scabies in otherwise healthy patients and in many patients with HIV infection.

Identification of host DNA by amplified fragment length polymorphism analysis: preliminary analysis of human crab louse (Anoplura: Pediculidae) excreta.

The ability to identify individual hosts of hematophagous arthropods via bloodmeal analyses is a continuing pursuit in both medical and forensic entomology. Characterization of human DNA from blood-feeding arthropods has been advanced substantially by preparation techniques, such as the polymerase chain reaction (PCR). Successful application of amplified fragment length polymorphism (AMP-FLP) analysis to excreta obtained from adult crab lice, Pthirus pubis (L.), fed on human volunteers is reported herein. Human DNA derived from crab louse excreta was typed successfully for two human DNA genetic markers, D1S80 and HUMTH01. Although preliminary, these results illustrate the ability of AMP-FLP analyses to provide individual human locus characterizations from desiccated arthropod excrement.

Seabather's eruption. Clinical, histologic, and immunologic features.

BACKGROUND: Seabather's eruption (SE) is a highly pruritic eruption under swimwear that occurs after bathing in the ocean. Its cause has been unknown. Few data have been collected since the classic description by Sams in 1949. OBJECTIVE: Our purpose was to describe the clinical and histopathologic findings in SE and to confirm the cause. METHODS: Patients with a pruritic eruption that developed after swimming were seen within 1 week of onset. Skin biopsy specimens and sera were obtained in selected cases. Water samples taken from areas of active SE outbreaks were examined for a causative organism. Sera were tested by enzyme-linked immunosorbent assay for reactivity to this organism. RESULTS: In southeast Florida, during a 4-month period, 70 patients with SE were seen. Inflammatory papules and pruritus were noted within hours of exposure. Eruptions were maximal in areas covered by a bathing suit. Children were more likely than adults to have systemic symptoms. The average duration of the eruption and pruritus was 12.5 days, with recurrences in 4.3% of patients. Histopathologic examination revealed a superficial and deep perivascular and interstitial infiltrate consisting of lymphocytes, neutrophils, and eosinophils. Water samples contained many cnidarian larvae, later grown to maturity and identified as Linuche unguiculata (thimble jellyfish). Enzyme-linked immunosorbent assay demonstrated in patients' sera high IgG levels specific for L. unguiculata. CONCLUSION: SE is a severely pruritic marine dermatosis that resolves spontaneously within 2 weeks. Therapy is symptomatic but often ineffective. Sera from affected persons showed specific reactivity to L. unguiculata.

Community control of scabies: a model based on use of permethrin cream.

For 18 years treatment with lindane or crotamiton products has failed to stem the epidemic of scabies among the Kuna Indians in the San Blas islands of the Republic of Panama. Permethrin 5% cream was introduced as the only treatment in a programme to control scabies on an island of 756 inhabitants and involving workers recruited locally. Prevalence fell from 33% to less than 1% after every person was treated. As long as continued surveillance and treatment of newly introduced cases was maintained, prevalence of scabies remained below 1.5% for over 3 years. When supply of medication was interrupted for 3 weeks, prevalence rose to 3.6%. When control was lost after the US invasion of Panama, prevalence rose to 12% within 3 months. Bacterial skin infections decreased dramatically when scabies was controlled. Permethrin is safe and effective even in areas where this disease has become resistant to lindane.