1,721,100 research outputs found
The tick-borne rickettsia Cowdria ruminantium has a Chlamydia-like developmental cycle
Full text linkThe articles have been scanned in colour with a HP Scanjet 5590; 600dpi.
Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.The development of the tick-borne rickettsial pathogen Cowdria ruminantium (S stock) was studied in bovine umbilical endothelial (BUE) cell cultures and in goat choroid plexus, by light- and electron microscopy. Cowdria divided by binary fission within intracytoplasmic vacuoles resulting in large colonies of reticulate bodies. After three to four days in culture, reticulate bodies developed into smaller intermediate bodies characterized by an electron-dense core. Shortly before disruption of the host cells, intermediate bodies condensed further into electron-dense elementary bodies, which were released into the culture medium. Elementary bodies invade other endothelial cells thus initiating a new infectious cycle which lasts between 5 and 6 days. In the infected goat choroid plexus similar reticulate and intermediate bodies were identified within vacuoles of capillary endothelial cells. However, extracellular elementary bodies were not detected. Another stock of Cowdria (W) showed an identical developmental cycle as that of the S stock. The W isolate was also pathogenic for mice, making it possible to test the infectivity of reticulate and elementary bodies in these animals. Reticulate bodies appeared to be less infective than elementary bodies. The developmental cycle of Cowdria resembles the cycle known to occur in Chlamydia. Moreover, Cowdria has other similarities with Chlamydia. It has a Gram-negative envelope, it does not store iodine-stainable carbohydrates and may lack peptidoglycan as does Chlamydia. It is concluded, that Cowdria and Chlamydia are to a certain extent related, confirming a recent report that both organisms have certain antigenic determinants in common. Since Cowdria is also related to Ehrlichia it may well be that Cowdria takes an intermediate position between Chlamydia and Ehrlichia. The phylogenetic relationship between Cowdria and Chlamydia and also with Ehrlichia should be further elucidated by molecular analysis using 16S ribosomal DNA sequences.European Community (Directorate General XII).mn201
Integrated control of ticks and fleas on dogs with particular reference to the prevention of vector-borne diseases
No full textBecause dogs are such loved companion animals, their health and wellbeing is of great importance to their human companions. Moreover, controlling ticks and fleas on dogs is also important in respect of the zoonotic risk that some of these parasites pose to their human companions. Numerous products are available to veterinarians and dog owners for controlling ticks and fleas. By comparing the efficacy of these products, important information can be collected that will help the end-user to decide on the most appropriate product. It was hypothesized that the combination of different active substances and alternative routes of administration using improved delivery systems, could enhance the speed of kill as well as duration of efficacy of various compounds. Moreover, if the speed of kill was rapid enough, these products could potentially prevent infections with tick-borne and flea-borne pathogens. Therefore the aim of the studies described in this thesis was to evaluate and compare the efficacy of various classes of compounds, with different modes of action, used for the control of tick and flea infestation on dogs. The efficacy of these compounds was evaluated either separately, or administered in combination, using different application modes, such as topical application, impregnated collars or oral formulations. Moreover, the ability of several compounds to prevent transmission of selected tick- and flea-borne pathogens was also assessed. In Chapter 2 the efficacy of various compounds against Haemaphysalis elliptica, Dermacentor reticulatus and Rhipicephalus sanguineus as well as Ctenocephalides felis was evaluated on dogs in controlled laboratory studies. In order to protect a dog from the detrimental effects of tick infestation pharmaceutical products must not only be able to control ticks, but the onset of action must be fast enough to prevent transmission of harmful tick-borne pathogens. In Chapter 3 the ability of different compounds to prevent the transmission of the tick-borne pathogen Babesia canis by Dermacentor reticulatus is evaluated in controlled laboratory studies. In Chapter 4 the ability of different compounds to prevent the transmission of the tick-borne pathogen Ehrlichia canis by Rhipicephalus sanguineus is evaluated in controlled laboratory studies. Moreover, the speed of transmission of E. canis by infected R. sanguineus was evaluated and compared in vivo on dogs and in vitro on artificial feeding membranes. Finally, in addition to the immediate irritation that flea infestations cause to dogs, fleas are also intermediate hosts of the metacestode stages of the cestode Dipylidium caninum. In Chapter 5 the prophylactic effectiveness of a collar formulation against infected fleas is evaluated and consequently also its ability to prevent D. caninum infection in dogs
Efficacy of fipronil against Amblyomma hebraeum ticks on boer goats and detection of Ehrlichia ruminantium in ticks in Limpopo Province, South Africa
Full text linkDissertation (MSc)--University of Pretoria, 2018.Heartwater, caused by Ehrlichia ruminantium, causes significant economic losses to commercial small stock farmers, including commercial boer goat farmers in the Limpopo Province of South Africa. Heartwater is endemic in this region where Amblyomma hebraeum, the South African bont tick and the vector for this disease occurs. Due to their long mouthparts and specific attachment sites on goats, A. hebraeum is also associated with wounds, secondary abscess formation and lameness. Small stock farmers in the Limpopo Province employ various methods to control A. hebraeum and the negative effects associated with this tick, including heartwater.
Two approaches where followed to focus on the control of A. hebraeum on the one hand and the detection and cryo-preservation of E. ruminantium from A. hebraeum on the other hand. The aim of this study was therefore twofold. By firstly determining the efficacy of a 1.0% fipronil pour-on solution against A. hebraeum by performing a therapeutic- and persistent efficacy trial and secondly to detect and cryo-preserve E. ruminantium from A. hebraeum ticks from a heartwater endemic region in the Limpopo province of South Africa. It was demonstrated that a 1.0% fipronil pour-on solution is 100% effective and has a persistent efficacy of seven days against A. hebraeum, but only if a targeted treatment approach is followed whereby the pour-on solution is applied to the predilection sites of A. hebraeum. A 1.0% fipronil pour-on solution can therefore be used by boer goat farmers to control A. hebraeum and the negative effects associated with this tick.
In order to detect and cryo-preserve E. ruminantium from A. hebraeum ticks, ground-up-tick-supernatant samples were prepared in the laboratory from A. hebraeum ticks collected from goats and cattle at specified time intervals. To determine whether E. ruminantium was present in A. hebraeum ticks, DNA extraction, nested PCR of the pCS20 region of the E. ruminantium genome and demonstration of the amplified DNA by agarose gel electrophoresis was performed. The results demonstrated that E. ruminantium was indeed present in eight out of eight ground-up-tick-supernatant samples that were cryo-preserved. In future research, these samples may become very useful for isolating current strains of heartwater, which will ultimately lead to a better understanding of the disease and to facilitate the implementation of novel control methods.Veterinary Tropical DiseasesMSc (Tropical Animal Health)Unrestricte
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A review of the role of pheromones in the control of Amblyomma ticks on livestock
Full text linkMini Dissertation (MSc (Tropical Animal Health))--University of Pretoria, 2020.As external parasites of livestock, ticks of the genus Amblyomma have a significant impact on animal health and production globally. Furthermore, Amblyomma ticks are vectors of diseases affecting livestock, but humans as well. Amblyomma variegatum and Amblyomma hebraeum, both found in Southern Africa, are vectors of heartwater (Ehrlichia ruminantium) and African tick bite fever (Rickettsia africae) affecting ruminants and humans, respectively. Beyond the current impact on animal and human health, there is potential for even more significant effects on animal production if the geographic range of these tick-borne pathogens will shift and expand beyond the traditional endemic areas.
A literature study was performed to evaluate the constituents of the attraction-aggregation-attachment (AAA) pheromones emitted by Amblyomma ticks and their effects on the behaviour of these ticks. Previous applications of these pheromones in tick control were studied and the difficulties experienced in field studies evaluated. Here, a novel method of tick control on cattle is proposed, based on the use of a legband impregnated with pheromones and acaricides, to attract and kill Amblyomma ticks. Specific recommendations are made to assess the efficacy and feasibility of such a control device under field conditions.Veterinary Tropical DiseasesMSc (Tropical Animal Health)Unrestricte
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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