No description available.

The Russian wheat aphid, Diuraphis noxia is one of the most destructive exotic invaders of South Africa, capable of reducing individual wheat plant yields by up to 90%. Entomopathogenic fungi are important natural mortality factors associated with this aphid in its Eurasian endemic habitats as well as in the United States and Canada; their impact often exceeding that of predators and parasitoids. The principal objectives of this study included (1) baseline characterization of the aphid-pathogenic flora associated with aphids from South Africa, with special reference to six common cereal aphids, (2) quantification of the comparative impact of the different fungal species on the cereal-aphid complex in three different wheat producing regions of South Africa, (3) field evaluation of the Hyphomycete Beauveria bassiana against D. noxia on resistant wheat, (4) screening of six fungicides for their potential usage in managing entomophthoralean epizootics within greenhouse rearings of the Russian wheat aphid, and (5) development and evaluation of a novel bioassay protocol for screening entomopathogenic Hyphomycetes against D. noxia. A total of nine species of fungi known to infect and kill aphid hosts were collected, including the six entomophthoraleans, Pandora neoaphidis, Conidiobolus thromboides, Conidiobolus obscurus, Entomophthora planchoniana, Conidiobolus coronatus and Neozygites fresenii, and three Hyphomycetes, Beauveria bassiana, Verticillium lecanii, and Paecilomyces farinosus. The former four entomophthoraleans are considered first reports from this country. For the first time, morphological characteristics of these nine South African-collected species are visually depicted and techniques for their isolation and in vitro culture discussed. Seven species of fungi were recorded from D. noxia, of which P. neoaphidis was the most important, causing up to 50% mortality during the late season under dryland conditions in the summer-rainfall region. Mycoses at epizootic levels, together with the large diversity of fungal species recorded from this host, indicated a high level of susceptibility to fungal infection. In contrast, infection of the oat aphid Rhopalosiphum padi remained < 5% despite favourable numbers of hosts and apparently suitable environmental conditions. This phenomenon strongly suggests some level of low susceptibility to fungal infection in this species. Under irrigated conditions m KwaZulu-Natal, the rose-gram aphid Metopolophium dirhodum was the predominant aphid but remained below economical injury levels. Field surveys revealed that this aphid was effectively targeted by P. neoaphidis and C. obscurus, and findings suggest that in some areas of South Africa entomophthoralean fungi effectively suppress this aphid, negating the need for insecticide applications. On average, ca. 61% control of D. noxia on resistant wheat was observed following an application of B. bassiana (5 x 10¹³ conidia per hectare) during the early flag-leaf stage of the wheat. Efficacy of B. bassiana applications on younger plants appeared to be influenced by the level of aphid activity, possibly explained by secondary pick-up of inoculum by D. noxia. These findings accentuate the importance of understanding the tritrophic relationship between host plant, pest and pathogen. The fungicides copper oxychloride, mancozeb + oxadixyl, captab + metalaxyl, bittertanol, iprodione, and mancozeb at a rate of 0.1% active ingredient moderately to strongly inhibited C. thromboides vegetative growth (mean inhibition 81.1 %). Mancozeb at concentrations of 10.0, 2.0, 1.25, 0.5, 0.08, and 0.016% was further evaluated in vitro. The fungus growth cut-off point, midway between 1.25 and 2.0% mancozeb, was calculated and a rate of 1.625% active ingredient per litre of water was used to decontaminate the fungus-infected D. noxia cultures. A novel bioassay protocol was developed, employing live host plants for rearing aphids post inoculation. Using this design against D. noxia, an average LC₅₀ estimate of 85 conidia per mm² for B. bassiana strain GHA was calculated. Control mortality was restricted to levels below 4%. The data indicated high precision due to an average coefficient of variation for slope of less than 20%, and an average chi-squared value of 5.46 ± 2.74 (n = 10 assays). The design will accommodate the use of cereal aphid species other than D. noxia, while live host plants will facilitate tritrophic studies on the effect of host-plant resistance on fungus-induced mortality of D. noxia. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2002.

Persistent organic pollutants (POPs) are a threat to the environment and human health because they are ubiquitous, resistant to degradation, can bio-accumulate in organisms and bio-magnify in food chains. They have a detrimental effect on the reproductive, nervous and immunity systems of vertebrates. An international treaty, the Stockholm Convention on POPs, came into force in 2004 and aims to limit and eventually prohibit any use and unintentional production of POPs. South Africa ratified the Convention in 2002. Those compounds currently listed by the Stockholm Convention as POPs include chlorinated pesticides such as dichlorodiphenyltrichlorethane (DDT), chlordane and dieldrin, and industry-related compounds such as polychlorinated biphenyls (PCBs) and hexachlorobenzene. Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are also regarded as POPs but - together with some PCBs - they are the unintentional result of anthropogenic activity. This study focussed on the PCDDs, PCDFs and dioxin-like PCBs in the aquatic environment of South Africa particularly because the water resources in this country are under pressure. Despite the fact that South Africa has the sources of these compounds, little is known about the levels of these three groups of compounds. The concentration of twelve dioxin-like PCBs, seven PCDDs and ten PCDFs were determined for 22 sites selected on the grounds of their proximity to possible pollution sources. Analytical determinations included gas chromatography/mass spectrometry and a cell-based bio-assay, the H4IIE-/17C reporter gene assay. Possible sources of the observed pollution were inferred using the following statistical investigative methods: principal component and hierarchical cluster analysis. Seven of the sites had levels higher than the threshold effect concentration of Canada's sediment quality guidelines of 0.85 ngTEQ kg'1 (Toxic Equivalency Quotient). The other sites had lower levels. The highest concentration, 17.8 ng TEQ kg"1, was measured at a site in the southern Gauteng Province. Most of the PCDD/F pollution seemed to have come from combustion sources related to human activity, rather than industrial combustion. Most of the dioxin-like PCB pollution seemed to have been from commercial PCB preparations. Future research would require better characterisation of the sources in order to reduce the formation of these compounds, but also to better understand the exposure and risk scenarios, if humans are to be in close contact with these sources. / Thesis (Ph.D. (Zoology))--North-West University, Potchefstroom Campus, 2008.

For a long time research has focused on the protein-coding mRNA, but there is a complex world of non-coding RNAs regulating the human body that we yet know very little about. Non-coding RNAs (ncRNAs) are involved in modulation of different cell processes including proliferation, differentiation and apoptosis. In the current study the role of ncRNAs in T cell activation and function was investigated. T cells are important mediators of immune responses, for example upon viral infections. The T helper cells (TH or CD4+ cells) are involved in orchestrating immune processes like aiding the activation of macrophages and enhancement of B cell function. The TH1 cell subtype is generally pro-inflammatory and IFNγ-secreting. There are regulatory T (Treg) cells that are involved in downregulation of TH1 cells, to decrease or terminate the immune response. It has been shown that upon repeated stimulation TH1 cells can switch into a Treg-like IL10-secreting anti-inflammatory phenotype. In the IL10-secreting Treg-like cells the microRNA 150 (miR-150) was found upregulated compared to IFNγ-secreting TH1 cells. Thus, miR-150 was believed to be a candidate in key regulation of the switch between the two phenotypes. Predicted target genes of miR-150 were identified using mRNA arrays investigating down-regulated genes in the IL10-secreting Treg-like subpopulation. In this thesis predicted targets of miR-150 were investigated using luciferase assays. Unfortunately no targets were identified. Upon isolation of IFNγ-secreting TH1 cells and Treg-like IL10-secreting cells, it was found that the ncRNA 886 (nc886) was upregulated in these activated cells, compared to resting TH cells. This indicates that nc886 has an important role in T cell activation. Nc886 has been shown to inhibit PKR activation in other cell types. The effect of nc886 on protein kinase R (PKR) was therefore investigated. PKR shuts down translation upon activation in response to viral double-stranded RNA or cellular stress. We showed that in an activated T cell phenotype nc886 is affecting PKR upon activation by dsRNA from HIV or synthetic origin. The PKR activation pattern is reversed in a resting T cell phenotype.

Increased reactive oxygen species (ROS) have been reported to be at the centre of various diseases. Although several reports have implicated elevated levels of ROS in the pathogenesis of diabetes mellitus, the early detection of ROS is still not attainable. This limitation causes difficulty in the early diagnosis of ROS related disorders. The presence of high levels of ROS was reported to result in differential expression of antioxidant genes involved in protecting cells from their deleterious effects. Among the antioxidant genes that are expressed, it was postulated that expression of metallothioneins (MTs) are also induced. MTs are low molecular weight, cysteine-rich proteins involved in metal homeostasis and reported to harbour antioxidant function. The aim of this investigation was to explore MTs as biomarkers for elevated levels of ROS in whole blood of type 2 diabetic (T2D) individuals. The level of ROS in diabetic, non-diabetic as well as individuals at risk of developing T2D was determined via the use of biochemical assays. Real-Time PCR was utilised to analyse the expression of MTs and the presence of MT proteins was analysed via the ELISA. In this study it was observed that diabetic individuals had elevated levels of ROS. However, no significant difference in the expression of MTs and the presence of MT proteins between the diabetic and non-diabetic individuals was observed. In vitro experimental conditions indicated that MT expression is induced by elevated levels of ROS. In pathological conditions the ROS-dependent induction of MT expression needs to be elucidated further. It therefore can be suggested that MTs can not yet be utilised as biomarkers for the detection of elevated levels of ROS in pathological conditions with ROS aetiology. This investigation also highlights the fact that blood is not an optimal medium in which this objective can be attained. / Thesis (Ph.D. (Biochemistry))--North-West University, Potchefstroom Campus, 2005.

POPs are a group of chemicals that have been extensively studied over the last few years. The main reason that these chemicals have received so much scientific attention is the myriad of negative effects they have on the environment and human health. The properties that cause the deleterious effects include a high molecular stability, rendering them highly persistent. Added to this is the lipophilic and hydrophobic nature of the compounds. POPs will thus tend to bio-accumulate and bio-magnify in the environment, causing a direct threat to humans and wildlife. To address this threat, the Stockholm Convention on Persistent Organic Pollutants, under the supervision of United Nations Environment programme (UNEP), was initiated and became legally binding on 17 May 2004. All countries, including South Africa, which ratified this agreement, will be expected to monitor and regulate the formation of POPs. Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) are all members of the dioxin-like family of POPs. This family of chemicals pose serious health threats such as carcinogenic effects and negative effects on reproduction. These substances, with the exception of PCBs, are formed unintentionally as by-products of industrial and thermal processes. One of the main sources of dioxin-like chemicals is medical waste incinerators. In this project the area surrounding a medical waste incinerator was monitored using a bio-assay technique. The determination of dioxin concentrations is usually preformed by chemical analysis, however, bio-assays have proven themselves to be a cheaper and time-saving screening method. The Toxic Equivalency Quotient (TEQs) determined through bio-assays can support chemical analysis in determining biologically-relevant risk assessments since bio-assay data has ecotoxicological relevance. These assays represent an integrated biological response to chemical pollutants, where biological effects are accounted for which is not possible in chemical analyses. One of the bio-assays used in the determination of the dioxin-like chemical TEQ is the H411 E reporter gene bio-assay. This assay is based on the Ah-receptor mediated toxicity of dioxin-like chemicals. Using this technique the TEQs for areas surrounding an active incinerator were determined, to indicate the distribution of these substances. The TEQs for the soil samples collected ranged between nondetectable and 154 ngTEQ/kg. There was no clear distributional pattern and the total organic carbon content in the soil did not seem to play a crucial role in the distribution of dioxin-like chemicals. Although a decrease in soil tillage showed a corresponding increase in TEQ. The predominant wind direction was taken into account but no correlation could be seen. However, meteorological parameters such as the ambient temperature and low precipitation in the area may have contributed to lower TEQ values. Cytotoxicity excluded data points and the phenomenon has to be addressed. High TEQ values in a residential area where free-range chickens are raised pose a serious concern to the level of dietary dioxin-like chemical intake. Eggs in the area could theoretically contain between 2.75 and 28.75 pgTEQ/g egg fat. Further studies are needed to determine how much dioxin-like chemicals are being transferred to humans through the consumption of free-range eggs / Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2006.

Petrol attendants are exposed to petrol volatile organic compounds (VOCs) which may have genotoxic and carcinogenic effects. The single cell gel electrophoresis assay (comet assay) is a method highly sensitive to DNA damage induced by environmental and occupational exposure to carcinogenic and mutagenic agents. The aim of this study was to evaluate the level of exposure of petrol attendants to petrol VOCs and also to determine their effect on DNA damage and repair in lymphocytes of African petrol attendants. The exposed group consisted of 20 subjects, randomly selected from three petrol stations. A control group of 20 unexposed subjects was also chosen and matched for age and smoking habits with the exposed group. Sorbent tubes were used to assess personal exposure of petrol attendants. The comet assay was used to investigate the basal DNA damage and repair capacity in isolated lymphocytes of petrol attendants and control subjects. Blood samples were taken from the petrol attendants at the end of their 8 hour working shift and also from the control subjects. The petrol attendants were found to be exposed to levels of petrol VOCs lower than the occupational exposure limit (OEL) for constituent chemicals. A significant relationship was found between the volume of petrol sold during the shift and the average concentrations of benzene, toluene and the total VOCs measured. However, relative humidity had a negative correlation with the average concentrations of benzene, toluene, xylene and the total VOCs. Significantly higher basal DNA damage was observed with the exposed group compared to the control group. The period of exposure influenced the level of DNA damage and the calculated repair capacity. Smoking and age had a significant influence on the level of DNA damage. DNA repair capacity was delayed in smokers of both exposed and non-exposed group. / Thesis (M.Sc. (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2008.

Regular physical activity (PA) leads to an increased quality of life by means of certain physiological adaptations. Regular PA is beneficial to the human body and its functionality, including the physiological, biochemical and even psychological modalities. During PA an increased burden is placed on all physiological mechanisms due to the increased energy demand, resulting in an adaptation of the physiological systems. Currently the biochemical mechanisms by which these adaptations occur are not well understood or defined. During the flow of electrons through the electron transport chain in the mitochondria free radicals and reactive oxygen species (ROS) are produced. PA results in increased ROS production. The relationship of different exercise intensities and ROS production with resulting DNA damage is unclear. These free radicals and ROS disturb the pro-oxidant anti-oxidant balance resulting in oxidative stress. When this balance is disturbed oxidative stress could lead to potential oxidative damage, Oxidative damage occurs in lipid, protein and nucleic acid macromolecules. ROS can attack DNA bases or deoxyribose residues to produce damaged bases and/or single and double strand breaks. When the DNA is regarded and the damages are replicated it could cause mutations or apoptosis, affecting the cell function and physiology. The purpose of this study was to investigate the influence of different aerobic intensities on oxidative DNA damage and repair in middle aged men by means of the Comet assay. Five PA males and five physically inactive males were assigned to an experimental and control group respectively. The subjects did not differ significantly at baseline. The VO2-max of each subject was determined at baseline. Subjects were then randomly assigned to 60, 70, 80 and 90% of individual baseline VO2-max intensities for an acute exercise intervention of 30 minutes on a bicycle ergometer. Blood sampling was done at baseline, post-exercise and 24 hours post-exercise for oxygen radical absorbance capacity (ORAC) and hydroperoxide analysis (dROM). Peripheral blood was obtained for DNA damage testing by means of Comet analysis at baseline, post-exercise, 5, 15, 30 minutes, and also 6, 12, 24, 48 and 72 hours after exercise. The results obtained indicated that subjects who regularly participate in PA had an increased baseline reading of ORAC and dROM values. ORAC levels after each acute exercise session increased, with the highest increase in the control group, with a decrease in the direction of baseline readings 24 hours post exercise. A biphasic damage-repair cycle over the 72 hour period was observed with the Comet analysis. The most damaged cells occur directly after acute exercise. The highest incidence of DNA damage over a 72 hour period was observed at 70% VO2-max, with the least amount of damage after 90% VO2-max. In conclusion the study indicates stress proteins or other kinds of physiological reaction to minimize the damaging effect of oxidative stress, is in place to restore the cell's homeostasis. Thus PA results in the development of oxidative DNA damage. To minimize DNA damage the optimal intensity for acute physical exercise is between 70-80% VO2-max. At higher intensities the release of stress proteins are initiated to buffer the damaging effect of oxidative stress and to restore homeostasis. / Thesis (M.Sc. (Human Movement Science))--North-West University, Potchefstroom Campus, 2007.

Water resources in South Africa are scarce, and should therefore be protected against pollutants, also from persistent organic pollutants (POPs). POPs are a global concern due to their ubiquitous presence, persistence and toxicity. This is emphasised by the Stockholm Convention on POPs, which aims at reducing and ultimately eliminating them. South Africa signed and ratified the treaty, and it became international law on 17 May 2004, but there is still a lack of information regarding POPs in South Africa. This study focussed on establishing the levels of POPs and other organic pollutants, which included various organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), dioxin-like compounds (DLCs), non-dioxin-like polychlorinated biphenyls (PCBs) and polybrominated diphenyl ether (PBDE). Sampling regions included the industrial cities – Cape Town, Richards Bay, Durban and Bloemfontein, and low-income, high density residential areas surrounding a wetland in Soweto/Lenasia and Botshabelo. Additionally, rivers flowing into neighbouring countries, rivers in the vicinity of paper and pulp producers and high altitude rivers were included. Sediment samples were firstly screened for the presence of DLCs by the H4IIE-luc bio-assay, whereafter sites eliciting quantifiable responses were selected for further chemical analysis by high resolution gas chromatography-high resolution mass spectrometry (HRGC/HRMS). Of the 96 sites, only 23 had quantifiable levels of DLCs. These sites were mainly of industrial, semi-industrial or low-income residential nature. PAHs were the predominant class of compounds at most of the sites, while OCPs and PCBs were present in moderate concentrations and PBDEs in minor concentrations. The concentration of pollutants measured in South African soils and sediments were intermediate when compared to the levels measured in some European, Asian and Scandinavian countries, with the exception of a few sites where exceptionally high levels of compounds were measured. The carbon content normalized concentrations of certain compounds at some of the sites exceeded the Canadian sediment quality guidelines. The estimated cancer risk associated with dermal absorption of OCPs measured in this study was negligible when compared to the background cancer risk expected for South Africans due to life style factors. However, it was estimated that dermal exposure to PCBs, DLCs and PAHs may lead to severe increases in cancer cases, and may seriously impact on human health. / Thesis (Ph.D. (Environmental Science))--North-West University, Potchefstroom Campus, 2011.

The Plasmodium falciparum parasite, carried by Anopheles mosquitoes, is currently a global problem due to the rising incidence of resistance of the parasite to available antimalaria drugs. Resistance and difficult treatment groups, including pregnant woman and young children, are pressing for the development of new, safe and effective prophylactic and treatment antimalarials. Because of the extensive process of developing new drugs, researchers and health care professionals have turned to combination therapy where a fast acting antimalarial is combined with slower acting drugs, such as antibiotics. The macrolide antibiotics, erytbromycin and azithromycin, have been studied to a limited extent for their potential antimalarial effect. Certain advantages, such as their safety profile (especially that of azithromycin) in pregnancy and administration to young children, motivates continual research into the advancement of the effect these drugs exude on malaria. Drug delivery systems contribute to the efficacy of medicines, conquering several difficulties of treatment with oral medication. Pheroid™ technology is a patented drug delivery system, mainly consisting of plant and essential fatty acids, and has been demonstrated to entrap, carry and deliver pharmacologically active compounds and other useful molecules. This study compared the in vitro effects of the macrolide antibiotics on the growth of a chloroquine-resistant strain (RSA 11) of Plasmodium falciparum to the effects of the macrolides entrapped in Pheroid™ vesicles on the same strain over and extended observation period of 144 hours. ELISA assays were conducted by analysing the HRP II (histidine-rich protein) levels on a pre-coated microtitre plate. The effects of the type of formulation, concentration and time were compared. The in vitro difference between erythromycin alone and entrapped in Pheroid™ vesicles were found to be statistically significant (p = 0.000000) while the effects of both formulations did not seem to be concentration dependant (p = 0.628424). Prolonged exposure was also statistically meaningful (p = 0.008268), though it seems that exposure need not exceed 96 hours. The type of formulation, in the case of azithromycin (azithromycin alone vs. azitbromycin entrapped in Pheroid™ vesicles), proved statistically significant (P = 0.002572), while neither formulation seemed concentration dependant (P = 0.427731). Prolonged exposure was found to be statistically insignificant for azithromycin (P = 0.221941). / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2010.