Browsing by Author "Davids, Virginia"
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- ItemOpen AccessClinical utility of a commercial LAM-ELISA assay for TB diagnosis in HIV-infected patients using urine and sputum samples(Public Library of Science, 2010) Dheda, Keertan; Davids, Virginia; Lenders, Laura; Roberts, Teri; Meldau, Richard; Ling, Daphne; Brunet, Laurence; Smit, Richard van Zyl; Peter, Jonathan; Green, Clare; Badri, Motasim; Sechi, Leonardo; Sharma, Surendra; Hoelscher, Michael; Dawson, RodneyBACKGROUND: The accurate diagnosis of TB in HIV-infected patients, particularly with advanced immunosuppression, is difficult. Recent studies indicate that a lipoarabinomannan (LAM) assay (Clearview-TB®-ELISA) may have some utility for the diagnosis of TB in HIV-infected patients; however, the precise subgroup that may benefit from this technology requires clarification. The utility of LAM in sputum samples has, hitherto, not been evaluated. METHODS: LAM was measured in sputum and urine samples obtained from 500 consecutively recruited ambulant patients, with suspected TB, from 2 primary care clinics in South Africa. Culture positivity for M. tuberculosis was used as the reference standard for TB diagnosis. RESULTS: Of 440 evaluable patients 120/387 (31%) were HIV-infected. Urine-LAM positivity was associated with HIV positivity (p = 0.007) and test sensitivity, although low, was significantly higher in HIV-infected compared to uninfected patients (21% versus 6%; p<0.001), and also in HIV-infected participants with a CD4 <200 versus >200 cells/mm 3 (37% versus 0%; p = 0.003). Urine-LAM remained highly specific in all 3 subgroups (95%-100%). 25% of smear-negative but culture-positive HIV-infected patients with a CD4 <200 cells/mm 3 were positive for urine-LAM. Sputum-LAM had good sensitivity (86%) but poor specificity (15%) likely due to test cross-reactivity with several mouth-residing organisms including actinomycetes and nocardia species. CONCLUSIONS: These preliminary data indicate that in a high burden primary care setting the diagnostic usefulness of urine-LAM is limited, as a rule-in test, to a specific patient subgroup i.e. smear-negative HIV-infected TB patients with a CD4 count <200 cells/mm 3 , who would otherwise have required further investigation. However, even in this group sensitivity was modest. Future and adequately powered studies in a primary care setting should now specifically target patients with suspected TB who have advanced HIV infection.
- ItemOpen AccessElevated levels of low molecular weight substances in the red cells of some mammalian species imply unsuspected antioxidant strategies(2009) Davids, Virginia; Harley, EricAn earlier observation by E.H. Harley (supervisor of this thesis) of curious metabolic anomalies in the red cells of black rhinoceros, and in particular a high free tyrosine level, suggested that a range of unusual, but presumeably physiological, processes might be found in mammalian red blood cells. As a follow-up to this, low molecular weight metabolites were examined in a range of mammalian species, using HPLC-based methods to compare levels in red cells with plasma levels. A remarkable interspecies diversity in red cell HPLC profiles was observed, with the unprecedented accumulation of substances including tyrosine, tryptophan, urate, and urate riboside occuring within the red cells of some species. Whereas novel evolutionary adaptations may characterise most of these species-specific variations, the ability of red cells to produce urate is proposed to be an inducible feature common to the red cells of many, or possibly even all, mammalian species. A surprisingly high degree of intraspecies genetic heterogeneity was evident in tyrosine and urate levels within horse, and urate riboside levels within cow red cells. This was in contrast with the greater homogeneity seen in levels of these and other low molecular weight substances in red cells from the other species evaluated. The next phase of investigation addressed the potential function(s) of these soluble substances accumulating within the red cell, particularly relating to a role in antioxidant defense. Using in vitro antioxidant assays such as the 'oxygen radical absorbance' (ORAC) and 'ferrous ion oxidation-xylenol orange' (FOX) assays, results were obtained consistent with a role for these substances as endogenous red cell antioxidants against a variety of reactive species produced by pathophysiological processes in the body. The demonstration that haemoglobin is involved in facilitating some of this activity further substantiates the idea that the red cell may be playing a crucial role in maintaining circulatory redox balance, and hence protecting other tissues from oxidative damage. If indeed such low molecular weight substances contribute to systemic antioxidant activity in some mammalian species, then apart from the intrinsic interest of such unexpected biological phenomena, these findings could pave the way for a plethora of further investigations, geared towards potential clinical applications (eg. as biomarkers or therapeutic approaches) in human and/or veterinary conditions associated with oxidative stress.
- ItemOpen AccessKunstdiva versus Stimmediva Callas and Sutherland in Bellini’s Norma(2019) Gunter, Leah; Davids, VirginiaThe focus of this dissertation is to analyse the balance between interpretative and vocal ability in bel canto opera, which is traditionally considered as the principal domain of the Stimmediva. The dissertation includes a survey of the characteristics of bel canto, Bellini’s contribution to it and the performance history of his opera Norma. Furthermore, it investigates the German differentiation between Kunstdiva and Stimmediva as exemplified by two major sopranos of the twentieth century, Maria Callas and Joan Sutherland. Callas’s performance of Norma is universally recognised as a watershed in the performance history of this role, and Sutherland is widely regarded as her most important immediate successor. Their distinct approaches to the scena from Act 1 of Norma are contrasted and compared. Three respondents were asked to evaluate recordings of this scena by these two artists with regard to style, technique and interpretation. Their responses are presented in table format, and a discussion of the insights that emerge from these form the final part of the dissertation. The conclusion notes the primacy of interpretative ability in the appreciation of vocal performance even within the bel canto style, but argues for a complete integration of dramatic and vocal skills in order to arrive at the ideal interpretation. Key words: Bel canto; Bellini; Callas; Casta diva; Fine al rito, e il sacro bosco…Ah! bello a meritorna; Kunstdiva; Norma; Scena; Sediziose voci; Stimmediva; Sutherland
- ItemOpen AccessMolecular detection of melanoma nodal metastases(2002) Davids, Virginia; Hanekom, Gideon; Kidson, SueThe aim of this study was to develop a practical and reproducible multi-marker RT-PCR essay, with the emphasis on achieving maximum specificity for the detection of melanoma nodal metastases. A novel protocol for the efficient homogenisation of nodal tissue was developed, with clinical applicability as the objective.