Browsing by Author "Esterhuizen, Johan"
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- ItemExplaining the host-finding behavior of blood-sucking insects : computerized simulation of the effects of habitat geometry on tsetse fly movement(PLoS, 2014-06) Vale, Glyn A.; Hargrove, John W.; Solano, Philippe; Courtin, Fabrice; Rayaisse, Jean-Baptiste; Lehane, Michael J.; Esterhuizen, Johan; Tirados, Inaki; Torr, Stephen J.Background: Male and female tsetse flies feed exclusively on vertebrate blood. While doing so they can transmit the diseases of sleeping sickness in humans and nagana in domestic stock. Knowledge of the host-orientated behavior of tsetse is important in designing bait methods of sampling and controlling the flies, and in understanding the epidemiology of the diseases. For this we must explain several puzzling distinctions in the behavior of the different sexes and species of tsetse. For example, why is it that the species occupying savannahs, unlike those of riverine habitats, appear strongly responsive to odor, rely mainly on large hosts, are repelled by humans, and are often shy of alighting on baits? Methodology/Principal Findings: A deterministic model that simulated fly mobility and host-finding success suggested that the behavioral distinctions between riverine, savannah and forest tsetse are due largely to habitat size and shape, and the extent to which dense bushes limit occupiable space within the habitats. These factors seemed effective primarily because they affect the daily displacement of tsetse, reducing it by up to ,70%. Sex differences in behavior are explicable by females being larger and more mobile than males. Conclusion/Significance: Habitat geometry and fly size provide a framework that can unify much of the behavior of all sexes and species of tsetse everywhere. The general expectation is that relatively immobile insects in restricted habitats tend to be less responsive to host odors and more catholic in their diet. This has profound implications for the optimization of bait technology for tsetse, mosquitoes, black flies and tabanids, and for the epidemiology of the diseases they transmit.
- ItemThe H.B. Thom Theatre : an evaluation of its potential as a regional arts and cultural centre(Stellenbosch : University of Stellenbosch, 2005-03) Esterhuizen, Johan; Hauptfleisch, Temple; University of Stellenbosch. Faculty of Arts and Social Sciences. Dept. of Drama.This study wishes primarily to explore re-positioning the H.B.Thom Theatre as a cultural amenity in the Stellenbosch region. The first step was to place the building of the H.B. Thom Theatre in 1966 in the context of the cultural and political dynamics of the time as well as to trace the cultural politics of the Western Cape in particular during the turbulent years leading to the first Democratic Elections in 1994. The question is asked, to what extent do the changes in the political climate and cultural thinking impact on the use of this important, regional arts facility? A Cultural Impact Study was made to evaluate the scope of cultural production in the region. Alongside this regional study, the past and present utilisation of the H.B.Thom Theatre as such has been thoroughly documented, processed and discussed. Areas of concern regarding the utilisation of the theatre in particular and possible solutions in meeting these concerns have been integrated into the study. The appropriate management structures and artistic vision leading to the establishment of the H.B.Thom Theatre as a Regional Arts Centre have been researched and detailed as well as mechanisms for its incorporation into the University of Stellenbosch’s broader Strategic Framework.
- ItemImproving the cost-effectiveness of visual devices for the control of riverine tsetse flies, the major vectors of Human African Trypanosomiasis(Public Library of Science, 2011-08-02) Esterhuizen, Johan; Rayaisse, Jean Baptiste; Tirados, Inaki; Mpiana, Serge; Solano, Philippe; Vale, Glyn A.; Lehane, Michael J.; Torr, Stephen J.Control of the Riverine (Palpalis) group of tsetse flies is normally achieved with stationary artificial devices such as traps or insecticide-treated targets. The efficiency of biconical traps (the standard control device), 1×1 m black targets and small 25×25 cm targets with flanking nets was compared using electrocuting sampling methods. The work was done on Glossina tachinoides and G. palpalis gambiensis (Burkina Faso), G. fuscipes quanzensis (Democratic Republic of Congo), G. f. martinii (Tanzania) and G. f. fuscipes (Kenya). The killing effectiveness (measured as the catch per m2 of cloth) for small targets plus flanking nets is 5.5-15X greater than for 1 m2 targets and 8.6-37.5X greater than for biconical traps. This has important implications for the costs of control of the Riverine group of tsetse vectors of sleeping sickness. © 2011 Esterhuizen et al.
- ItemTowards an optimal design of target for tsetse control : comparisons of novel targets for the control of Palpalis group tsetse in West Africa(PLoS, 2011-09) Rayaisse, Jean Baptiste; Esterhuizen, Johan; Tirados, Inaki; Kaba, Dramane; Salou, Ernest; Diarrassouba, Abdoulaye; Vale, Glyn A.; Lehane, Michael J.; Torr, Stephen J.; Solano, PhilippeBackground: Tsetse flies of the Palpalis group are the main vectors of sleeping sickness in Africa. Insecticide impregnated targets are one of the most effective tools for control. However, the cost of these devices still represents a constraint to their wider use. The objective was therefore to improve the cost effectiveness of currently used devices. Methodology/Principal Findings: Experiments were performed on three tsetse species, namely Glossina palpalis gambiensis and G. tachinoides in Burkina Faso and G. p. palpalis in Côte d'Ivoire. The 1×1 m2 black blue black target commonly used in W. Africa was used as the standard, and effects of changes in target size, shape, and the use of netting instead of black cloth were measured. Regarding overall target shape, we observed that horizontal targets (i.e. wider than they were high) killed 1.6-5x more G. p. gambiensis and G. tachinoides than vertical ones (i.e. higher than they were wide) (P<0.001). For the three tsetse species including G. p. palpalis, catches were highly correlated with the size of the target. However, beyond the size of 0.75 m, there was no increase in catches. Replacing the black cloth of the target by netting was the most cost efficient for all three species. Conclusion/Significance: Reducing the size of the current 1*1 m black-blue-black target to horizontal designs of around 50 cm and replacing black cloth by netting will improve cost effectiveness six-fold for both G. p. gambiensis and G. tachinoides. Studying the visual responses of tsetse to different designs of target has allowed us to design more cost-effective devices for the effective control of sleeping sickness and animal trypanosomiasis in Africa.
- ItemTsetse control and Gambian sleeping sickness; implications for control strategy(Public Library of Science, 2015-08) Tirados, Inaki; Esterhuizen, Johan; Mangwiro, T. N. Clement; Vale, Glyn A.; Hastings, Ian; Solano, Philippe; Lehane, Michael J.; Torr, Steve J.Background: Gambian sleeping sickness (human African trypanosomiasis, HAT) outbreaks are brought under control by case detection and treatment although it is recognised that this typically only reaches about 75% of the population. Vector control is capable of completely interrupting HAT transmission but is not used because it is considered too expensive and difficult to organise in resource-poor settings. We conducted a full scale field trial of a refined vector control technology to determine its utility in control of Gambian HAT. Methods and Findings: The major vector of Gambian HAT is the tsetse fly Glossina fuscipes which lives in the humid zone immediately adjacent to water bodies. From a series of preliminary trials we determined the number of tiny targets required to reduce G. fuscipes populations by more than 90%. Using these data for model calibration we predicted we needed a target density of 20 per linear km of river in riverine savannah to achieve >90% tsetse control. We then carried out a full scale, 500 km2 field trial covering two HAT foci in Northern Uganda to determine the efficacy of tiny targets (overall target density 5.7/km2). In 12 months, tsetse populations declined by more than 90%. As a guide we used a published HAT transmission model and calculated that a 72% reduction in tsetse population is required to stop transmission in those settings. Interpretation: The Ugandan census suggests population density in the HAT foci is approximately 500 per km2. The estimated cost for a single round of active case detection (excluding treatment), covering 80% of the population, is US$433,333 (WHO figures). One year of vector control organised within the country, which can completely stop HAT transmission, would cost US$42,700. The case for adding this method of vector control to case detection and treatment is strong. We outline how such a component could be organised. Author Summary: Sleeping sickness is controlled by case detection and treatment but this often only reaches less than 75% of the population. Vector control is capable of completely interrupting HAT transmission but is not used because of expense. We conducted a full scale field trial of a refined vector control technology. From preliminary trials we determined the number of insecticidal tiny targets required to control tsetse populations by more than 90%. We then carried out a full scale, 500 km2 field trial covering two HAT foci in Northern Uganda (overall target density 5.7/km2). In 12 months tsetse populations declined by more than 90%. A mathematical model suggested that a 72% reduction in tsetse population is required to stop transmission in those settings. The Ugandan census suggests population density in the HAT foci is approximately 500 per km2. The estimated cost for a single round of active case detection (excluding treatment), covering 80% of the population, is US$433,333 (WHO figures). One year of vector control organised within country, which can completely stop HAT transmission, would cost US$42,700. The case for adding this new method of vector control to case detection and treatment is strong. We outline how such a component could be organised.
- ItemVegetation and the importance of insecticide-treated target siting for control of glossina fuscipes fuscipes(Public Library of Science, 2011-09-20) Esterhuizen, Johan; Njiru, Basilio; Vale, Glyn A.; Lehane, Michael J.; Torr, Stephen J.Control of tsetse flies using insecticide-treated targets is often hampered by vegetation re-growth and encroachment which obscures a target and renders it less effective. Potentially this is of particular concern for the newly developed small targets (0.25 high × 0.5 m wide) which show promise for cost-efficient control of Palpalis group tsetse flies. Consequently the performance of a small target was investigated for Glossina fuscipes fuscipes in Kenya, when the target was obscured following the placement of vegetation to simulate various degrees of natural bush encroachment. Catches decreased significantly only when the target was obscured by more than 80%. Even if a small target is underneath a very low overhanging bush (0.5 m above ground), the numbers of G. f. fuscipes decreased by only about 30% compared to a target in the open. We show that the efficiency of the small targets, even in small (1 m diameter) clearings, is largely uncompromised by vegetation re-growth because G. f. fuscipes readily enter between and under vegetation. The essential characteristic is that there should be some openings between vegetation. This implies that for this important vector of HAT, and possibly other Palpalis group flies, a smaller initial clearance zone around targets can be made and longer interval between site maintenance visits is possible both of which will result in cost savings for large scale operations. We also investigated and discuss other site features e.g. large solid objects and position in relation to the water's edge in terms of the efficacy of the small targets.