Infection intensity-dependent accuracy of reagent strip for the diagnosis of Schistosoma haematobium and estimation of treatment prevalence thresholds

BackgroundReagent strip to detect microhematuria as a proxy for Schistosoma haematobium infections has been considered an alternative to urine filtration for individual diagnosis and community-based estimates of treatment needs for preventive chemotherapy. However, the diagnostic accuracy of reagent strip needs further investigation, particularly at low infection intensity levels.MethodsWe used existing data from a study conducted in Tanzania that employed urine filtration and reagent strip testing for S. haematobium in two villages, including a baseline and six follow-up surveys after praziquantel treatment representing a wide range of infection prevalence. We developed a Bayesian model linking individual S. haematobium egg count data based on urine filtration to reagent strip binary test results available on multiple days and estimated the relation between infection intensity and sensitivity of reagent strip. Furthermore, we simulated data from 3,000 hypothetical populations with varying mean infection intensity to infer on the relation between prevalence observed by urine filtration and the interpretation of reagent strip readings.Principal findingsReagent strip showed excellent sensitivity even for single measurement reaching 100% at around 15 eggs of S. haematobium per 10 ml of urine when traces on reagent strip were considered positive. The corresponding specificity was 97%. When traces were considered negative, the diagnostic accuracy of the reagent strip was equivalent to urine filtration data obtained on a single day. A 10% and 50% urine filtration prevalence based on a single day sampling corresponds to 11.2% and 48.6% prevalence by reagent strip, respectively, when traces were considered negative, and 17.6% and 57.7%, respectively, when traces were considered positive.Conclusions/SignificanceTrace results should be included in reagent strip readings when high sensitivity is required, but excluded when high specificity is needed. The observed prevalence of reagent strip results, when traces are considered negative, is a good proxy for prevalence estimates of S. haematobium infection by urine filtration on a single day.     

Studies of Impedance in Cardiac Tissue using Sucrose Gap and Computer Techniques: II. Circuit Simulation of Passive Electrical Properties and Cell-to-Cell Transmission

The impedance measured in a strip of heart tissue from the moth Hyalophora cecropia is fitted by circuit models of several configurations. The circuits include: (a) a single R-C circuit (b) a double R-C circuit (c) terminated transmission lines, and (d) a pattern of cells with cell-to-cell transmission paths. The last of these is found to give the best fit. Calculation of the model impedances and optimization of element values are performed by a computer. The possibility that the mechanism of cell-to-cell transmission may be capacitative rather than conductive is explored using values of capacitance derived from the circuit models to calculate the effect of capacitative coupling alone on signal transmission. The calculations show that sufficient voltage can be transmitted from the excited cell to an adjacent cell to effect excitation.     

Comparative Study of the Efficacy of Seven Paper-Reagent Strips and Conventional Biochemical Tests in Identifying Gram-negative Organisms

Gram-nagative organisms were tested with commercially available reagentimpregnated strips (PATHO-TEC). Of the 291 strains, all were tested by using seven paper tests and their conventional counterparts. Excellent correlation was obtained with the oxidase, phenylalanine-deaminase, and Voges-Proskauer tests. Indole tests made on liquid medium cultures also gave complete correlation, but some false-negative results with indole-positive Proteus strains were obtained when growth from solid medium was tested by the strip method. Paper strip urease tests were positive within 2 hr with all Klebsiella and some Serratia, Herellea, and Citrobacter strains as well as with Proteus strains. Approximately 15% of citrate strip test results differed from those of the conventional tests, and reproducibility was poor on retest. The lysine decarboxylase strip test showed a number of discrepancies and posed problems of interpretation and readability. Paper reagent strip methods are simple and convenient and merit further development to increase the specificity of those which depend on pH change up to that achieved with the Voges-Proskauer, oxidase, phenylalanine, and indole methods.     

Reagent Strips and Conventional Tests for Acid Production from Mannitol and Coagulase Activity of Staphylococcus: a Comparative Study

A total of 244 Staphylococcus strains were tested simultaneously for acid production from mannitol and for coagulase activity with reagent-impregnated paper strips and with their conventional counterparts. Significant correlation was obtained with 97.9% of the strains for mannitol and with 95% for the coagulase test. The paper strip method is a combined test for both mannitol and coagulase tests, thus making it more convenient and simpler than conventional methods. The results are obtained rapidly within 6 hr by the paper strip method. However, as the paper strip method is designed for the aerobic system, the conventional tests were also carried out under aerobic conditions to compare the results.     

植物凯氏带形成分子机制及功能特点的研究进展

凯氏带位于被子植物初生根内皮层细胞,环绕细胞1周,是与质膜紧密结合的非极性带状增厚结构。凯氏带作为植物根中离子径向运输障碍,调节离子的质外体吸收途径,迫使土壤中的离子通过内皮层细胞膜,选择性地进入中柱。凯氏带发现于1865年,但直至拟南芥凯氏带蛋白的发现和凯氏带阻滞作用物质基础被揭示,凯氏带的形成机理和功能才逐渐为人们所认知。凯氏带的物质基础为木质素,其形成需要由凯氏带蛋白和受体激酶组成的合成平台。细胞内部的木质素单体经ABCG载体运输到凯氏带的形成区,经ESB1dirigent蛋白、RBOHF氧化酶和PER64过氧化物酶等催化,合成木质素。该文对近年来国内外有关凯氏带形成的分子机制和功能特点方面的研究进展进行综述,为进一步理解和解析凯氏带的形成机理和功能提供参考。     

Inhibitory effect of essential oils of Allium sativum and Piper longum on spontaneous muscular activity of liver fluke, Fasciola gigantica

Effects of essential oil of Allium sativum (garlic) and Piper longum (Indian long pepper) were evaluated on muscular activity of whole Fasciola gigantica and its strip preparation. The whole flukes and longitudinal strip preparations of the flukes were isometrically mounted to record the spontaneous muscular activity (SMA) and to evaluate effects of cumulative doses (0.1, 0.3, 1.0 and 3.0 mg/ml) of the plant essential oils. Whole flukes and the strip preparations exhibited continuous SMA without any significant difference in its baseline tension, frequency and amplitude for 2 h. Essential oil of A. sativum produced significant reduction in the frequency and the amplitude of the SMA of whole fluke at 1 and 3 mg/ml concentrations. It caused complete paralysis of the fluke after 15 min of administration of 3 mg/ml concentration. Similar to whole fluke, essential oil of A. sativum (3 mg/ml) also produced flaccid paralysis in the strip preparations of the flukes. Essential oil of P. longum firstly induced marked excitatory effect and then there was flaccid paralysis of the whole fluke following 15 min exposure at 3 mg/ml concentration. Complete flaccid paralysis of the strip preparation was also ensued after 15 min of administration of 3 mg/ml concentration of P. longum. In both the essential oils, the whole fluke and strip preparations did not recover from paralysis following 2-3 washes. In conclusion, the observations demonstrated irreversible paralytic effect of essential oils of A. sativum and P. longum on F. giganticain vitro which might possibly help to developing herbal-based anthelmintic.     

Regeneration of Betula albosinensis in Strip Clearcut and Uncut Forests of the Qinling Mountains in China

To contribute to a better understanding of the regeneration strategy of Betula albosinensis forests and the likely reasons behind either the successful recovery or failure after strip clearcutting, we compared the population structures and spatial patterns of B. albosinensis in eight B. albosinensis stands in Qinling Mountains, China. Four cut and four uncut stands were selected, and each sampled using a single large plot (0.25 ha). Results indicated that, on the one hand, B. albosinensis recruitment was scarce (average of 48 stems ha⁻¹) in the uncut stands, relative to the mature population (average of 259 stems ha⁻¹), suggesting a failure of recruitment. On the other hand, the subsequent regeneration approximately 50 years after the strip clearcutting showed that the density of the target species seedlings and saplings has increased significantly, and the current average density of seedlings and saplings was 156 stems ha⁻¹. The clumped spatial pattern of B. albosinensis suggested that their regeneration was highly dependent on canopy disturbance. However, recruitment remained poor in the uncut stands because most gaps were small in scale. The successful regeneration of sunlight-loving B. albosinensis after strip clearcutting was attributed to the exposed land and availability of more sunlight. Bamboo density did not influence B. albosinensis recruitment in the uncut stands. However, stand regeneration was impeded after strip clearcutting; thus, removing bamboo is essential in improving the competitive status of B. albosinensis at the later stage of forest regeneration after clearcutting. The moderate severity of disturbance resulting from strip clearcutting reversed the degeneration trend of primary B. albosinensis stands. This outcome can help strike a balance between forest conservation and the demand for wood products by releasing space and exposing the forested land for recruitment. Life history traits and spatiotemporal disturbance magnitude are important factors to consider in implementing effective B. albosinensis regeneration strategies.     

Vitrification and transfer of cynomolgus monkey (Macaca fascicularis) embryos fertilized by intracytoplasmic sperm injection

Protocols for cryopreservation of monkey embryos are not well established. The objective of the current study was to determine the efficacy of the polypropylene strip method for cryopreserving cynomolgus monkey embryos. Cynomolgus monkey embryos, 63 and 56 at the 4- to 8-cell and 56 blastocyst stages, respectively, were produced by intracytoplasmic sperm injection and in vitro culture, and vitrified using a polypropylene strip. For these two stages, 95 and 86% survived after thawing and pregnancy rates were 29.2% (7 pregnant females/24 recipients, with three live births) and 0% (n = 16 recipients). These were apparently the first live births obtained from embryos fertilized by ICSI. In conclusion, 4- to 8-cell preimplantation cynomolgus monkey embryos were successfully cryopreserved using a polypropylene strip.     

Occurrence of Antimicrobial-Resistant Escherichia coli and Salmonella enterica in the Beef Cattle Production and Processing Continuum

Specific concerns have been raised that third-generation cephalosporin-resistant (3GC^r) Escherichia coli, trimethoprim-sulfamethoxazole-resistant (COT^r) E. coli, 3GC^r Salmonella enterica, and nalidixic acid-resistant (NAL^r) S. enterica may be present in cattle production environments, persist through beef processing, and contaminate final products. The prevalences and concentrations of these organisms were determined in feces and hides (at feedlot and processing plant), pre-evisceration carcasses, and final carcasses from three lots of fed cattle (n = 184). The prevalences and concentrations were further determined for strip loins from 103 of the carcasses. 3GC^r Salmonella was detected on 7.6% of hides during processing and was not detected on the final carcasses or strip loins. NAL^r S. enterica was detected on only one hide. 3GC^r E. coli and COT^r E. coli were detected on 100.0% of hides during processing. Concentrations of 3GC^r E. coli and COT^r E. coli on hides were correlated with pre-evisceration carcass contamination. 3GC^r E. coli and COT^r E. coli were each detected on only 0.5% of final carcasses and were not detected on strip loins. Five hundred and 42 isolates were screened for extraintestinal pathogenic E. coli (ExPEC) virulence-associated markers. Only two COT^r E. coli isolates from hides were ExPEC, indicating that fed cattle products are not a significant source of ExPEC causing human urinary tract infections. The very low prevalences of these organisms on final carcasses and their absence on strip loins demonstrate that current sanitary dressing procedures and processing interventions are effective against antimicrobial-resistant bacteria.     

The dynamics of a discrete population model with threshold

The dynamics of the discrete, scalar population model x_{k + 1} = ax²_k(1 – x_k) are investigated. In addition to density dependence, which has been studied previously by many, this equation models the threshold phenomenon. Some similarities to and differences from previous models are observed. In particular, for large a values this model exhibits chaos which is restricted to a nowhere dense Cantor set of measure 0. In order to explain this, a piecewise linear simplification of the model is considered. Other models exhibiting similar dynamics are also mentioned.     

A simple and rapid immunochromatographic test strip for detection of pathogenic isolates of Vibrio harveyi

Mouse monoclonal antibodies (MAbs) and rabbit polyclonal antibody (PAb) against Vibrio harveyi were generated from immunization of mice and rabbits with highly virulent isolate of V. harveyi. Two MAbs specific to virulent isolates of V. harveyi were obtained and one of them (VH4) was selected to conjugate with colloidal gold as the detector antibody was laid on a sample pad. Rabbit polyclonal antibody was used as the capture antibody at the test line (T) and goat anti-mouse IgG antibody (GAM) was used as the capture antibody at the control line (C) of nitrocellulose strip. The ready-to-use strip was held in a plastic case and then stored in a desiccated plastic bag. A sample volume of 100 μl of bacterial suspension from various sources mixed with application buffer was applied to the sample chamber at one end of the strip and allowed to flow by chromatography through the nitrocellulose membrane to the other end. In test samples containing virulent isolates of V. harveyi, the bacteria would bind to the monoclonal antibody conjugated with colloidal gold and the resulting complex would be captured by the antibodies at the test line to give a reddish-purple band. Any unbound monoclonal antibody conjugated with colloidal gold moved across the test line would be captured by the GAM and form a band at the control line (C). In sample without V. harveyi or with V. harveyi below the limit (< 10⁶ CFU/ml) of detection for the kit, only the control line band was observed. If the test sample was pre-enriched in tryptic soy broth (TSB) for 6 h before application to the strip, the sensitivity would increase to 1–10 CFU/ml which is comparable to that of PCR. This method could be used to detect pathogenic isolates of V. harveyi in pond water or infected shrimp in order to monitor and to reduce the risk of V. harveyi outbreak in the shrimp culture. The beneficial features of this kit are that simple, convenient and quick results (within 15 min) can be obtained without the requirement of sophisticated tools or special equipments and skills.     

A distribution model for Glossina brevipalpis and Glossina austeni in Southern Mozambique,Eswatini and South Africa for enhanced area-wide integrated pest management approaches

BackgroundGlossina austeni and Glossina brevipalpis (Diptera: Glossinidae) are the sole cyclical vectors of African trypanosomes in South Africa, Eswatini and southern Mozambique. These populations represent the southernmost distribution of tsetse flies on the African continent. Accurate knowledge of infested areas is a prerequisite to develop and implement efficient and cost-effective control strategies, and distribution models may reduce large-scale, extensive entomological surveys that are time consuming and expensive. The objective was to develop a MaxEnt species distribution model and habitat suitability maps for the southern tsetse belt of South Africa, Eswatini and southern Mozambique.Methodology/Principal findingsThe present study used existing entomological survey data of G. austeni and G. brevipalpis to develop a MaxEnt species distribution model and habitat suitability maps. Distribution models and a checkerboard analysis indicated an overlapping presence of the two species and the most suitable habitat for both species were protected areas and the coastal strip in KwaZulu-Natal Province, South Africa and Maputo Province, Mozambique. The predicted presence extents, to a small degree, into communal farming areas adjacent to the protected areas and coastline, especially in the Matutuíne District of Mozambique. The quality of the MaxEnt model was assessed using an independent data set and indicated good performance with high predictive power (AUC > 0.80 for both species).Conclusions/SignificanceThe models indicated that cattle density, land surface temperature and protected areas, in relation with vegetation are the main factors contributing to the distribution of the two tsetse species in the area. Changes in the climate, agricultural practices and land-use have had a significant and rapid impact on tsetse abundance in the area. The model predicted low habitat suitability in the Gaza and Inhambane Provinces of Mozambique, i.e., the area north of the Matutuíne District. This might indicate that the southern tsetse population is isolated from the main tsetse belt in the north of Mozambique. The updated distribution models will be useful for planning tsetse and trypanosomosis interventions in the area.     

The eastern swamp crayfish Gramastacus lacus sp. n. (Decapoda,Parastacidae) a new species of freshwater crayfish from coastal New South Wales,Australia

Gramastacus lacus sp. n., is described from coastal lowlands of the Central and Mid North Coast regions of New South Wales, Australia. Gramastacus lacus has a restricted distribution in ephemeral habitats, being dependent on regular natural flooding and drying cycles, and burrows for survival during temporary dry cycles. Documented are population distributions in lowland habitats (3–48 m, a.s.l.) from Wamberal Lagoon, north along the coastal strip to Wallis Lake. The species is small, reaching a maximum weight of 7 grams and 21.3 mm OCL, and distinguished by a large male genital papilla, large raised post orbital ridges, laterally compressed carapace and elongated chelae.     

Physiological Characteristics Underlying the Distribution Patterns of Luminous Bacteria in the Mediterranean Sea and the Gulf of Elat

Physiological characteristics of luminous bacteria isolated from the Mediterranean and Gulf of Elat were compared to determine their relationship to the specific seasonal and geographic distribution patterns of these bacteria. The effects of temperature on growth rate and yield, relative sensitivity to photooxidation, resistance to high salt concentration (8%), and ability to grow in nutrient-poor conditions appear to control these patterns. The winter appearance of Photobacterium fischeri and the succession of winter and summer types of Beneckea harveyi in the eastern Mediterranean are explained by different temperature requirements for growth. Sensitivity to photooxidation explains the disappearance of P. leiognathi, present in the main body of the Gulf of Elat throughout the year, from the shallow coastal strip. B. harveyi is present in this coastal strip which is higher in nutrients and in productivity than the open waters. Competition experiments between B. harveyi and P. leiognathi in batch and continuous culture indicate that the oligotrophic P. leiognathi is outcompeted by B. harveyi in rich and even in relatively poor media. The distribution pattern found in the Bardawil hypersaline lagoon is explained by selection of salinity-resistant mutants of B. harveyi from the Mediterranean Sea.     

The Evolution of One- and Two-Locus Systems

Assuming age-independent fertilities and mortalities and random mating, continuous-time models for a monoecious population are investigated for weak selection. A single locus with multiple alleles and two alleles at each of two loci are considered. A slow-selection analysis of diallelic and multiallelic two-locus models with discrete nonoverlapping generations is also presented. The selective differences may be functions of genotypic frequencies, but their rate of change due to their explicit dependence on time (if any) must be at most of the second order in s, (i.e., O( s²)), where s is the intensity of natural selection. Then, after several generations have elapsed, in the continuous time models the time-derivative of the deviations from Hardy-Weinberg proportions is of O(s²), and in the two-locus models the rate of change of the linkage disequilibrium is of O(s²). It follows that, if the rate of change of the genotypic fitnesses is smaller than second order in s (i.e., o(s²)), then to O(s²) the rate of change of the mean fitness of the population is equal to the genic variance. For a fixed value of s, however, no matter how small, the genic variance may occasionally be smaller in absolute value than the (possibly negative) lower order terms in the change in fitness, and hence the mean fitness may decrease. This happens if the allelic frequencies are changing extremely slowly, and hence occurs often very close to equilibrium. Some new expressions are derived for the change in mean fitness. It is shown that, with an error of O( s), the genotypic frequencies evolve as if the population were in Hardy-Weinberg proportions and linkage equilibrium. Thus, at least for the deterministic behavior of one and two loci, deviations from random combination appear to have very little evolutionary significance.     

The importance of models of infection in the study of disease resistance

Models currently occupy the crucial first step in the research flow for the development of new drugs and vaccines. Some animal models are better at reflecting the host–pathogen interaction in humans than others; this depends on the pathogen and its host specificity. Data gathered from what are often poorly adapted models provide a mosaic of sometimes contradictory information, yet there is little incentive to better delineate the relevance of models or to exploit recent advances to develop improved ones. This review reports on three particularly intractable human pathogens – Mycobacterium, Plasmodium and Schistosoma – and reflects that the extent to which these model systems mimic infection and protection processes in humans might not be sufficiently well defined.     

The amino acid composition of proteins: a method of analysis.

Four quasiloglinear models are proposed for describing relationships between the amino acid composition of proteins and the structure of the genetic code. The models allow estimation of base frequencies in all three codon positions and can be used to investigate “interactions” between any two codon positions. The estimation procedure proposed by Ohta and Kimura (Genetics64 (1970), 387–395) is discussed and using two of the proposed quasiloglinear models an analysis of the amino acid composition of human cytochrome c is presented. The analysis suggests that of the six codons which code for leucine (CUU, CUC, CUA and CUG) do not occur in human cytochrome c.     

The Casparian strip in pea epicotyls: Effects of light on its development

The Casparian strip, which is specific to roots, was studied in the epicotyls of dark-grown seedlings of pea (Pisum sativum L.) where it was found to have the same morphology and properties as the strip in roots. In dark-grown seedlings, the distance between the upper-most position of the Casparian strip and the bending point of the hook (about 37 mm) did not change during growth of the seedlings. In the uppermost 0.5-mm region of the region in which the Casparian strip could be detected by fluorescence microscopy, the plasma membrane was not firmly attached to the cell wall. The development of the Casparian strip continued for about 42 h after dark-grown seedlings were transferred to the light, indicating that (i) the cells that have been determined to form the Casparian strip in darkness form the strip in the light, and that (ii) it takes about 42 h for the cells to complete formation of the strip. Cells in the hook of dark-grown seedlings did not form a Casparian strip when such seedlings were transferred to the light. The Casparian strip was formed in rapidly elongating internodes of light-grown seedlings when the seedlings were transferred to darkness. Light did not control the formation of the Casparian strip in roots.Abbreviation PBS phosphate-buffered saline