No description available.

The aim of this study was to develop a sensitive and specific method of detecting Toxoplasma gondii in the immunocompromised host which would reduce the need for other tests and would ensure the prompt initiation of the appropriate treatment, the effects of which could be monitored. Such a system would also be of benefit in theinvestigation of parasite/host interaction. Initial work investigated an antigen ELISA and the PCR using two different gene targets CB 1 and P30) to find the most sensitive system. The ELISA was insensitive but both PCR systems were capable of detecting parasite in blood, lymph and tissue samples from experimentally infected sheep. The B 1 PCR detected parasite earlier and over a significantly longer period than the P30 PCR, this greater sensitivity being due to the higher copy number of the B 1 gene. The PCR was applied to samples from patients with AIDS with the aim of finding an ideal sample for the diagnosis of infection. Parasite was detected in blood up to a month prior to clinical signs of infection, and therefore blood samples are ideal for monitoringpatients at risk of recrudescence of a chronic infection. This result indicates that recrudescence is not due to local reactivation, but is due to a more widespread parasitaemia. However, as parasitaemia was shown to be transient in cases of recrudescence, sampling time may be critical. Parasite was also detected in urine, biopsytissue and post mortem material, but was not detected in CSF.Dexamethasone was used to create a mouse model of recrudescence in the immunocompromised patient to further investigate interaction between the parasite and host. The PCR detected parasite in blood, brain and heart of chronically infected animals, however the detection rate was significantly higher in groups receiveing immunosuppressive therapy. Dexamethasone treatment mimicked the effects seen in the AIDS population where 30-35% of chronically infected individuals showed clinical signsof toxoplasmosis. However the PCR may also be detecting latent cysts in tissue samples, and blood samples were occasionally positive without clinical evidence of infection. This could be due to small amounts of parasite circulating intermittently, or to breakdownproducts from parasite degradation. There was therefore a need to differentiate between active and chronic infection, and this was carried out by developing a quantitative PCR based on competitive amplification. A novel Sma I restriction site was created within the P30 gene, and known amounts were co-amplified with samples. The amplified products were then digested with Sma I to differentiate between mutated and T. gondii DNA and the point at which product yield was equalled indicated the amount of original DNA present in the sample. The system was shown to work using human PM samples, and could be adapted to indicate a cut-off point where parasite DNA levels reveal active infection. In conclusion the B 1 PCR is the method of choice in detecting T. gondii in AIDS patients. Any patient in which active parasite is detected should be treated and closely monitored using the qPCR for any evidence of reactivation.

No description available.

The ability to mount an efficient immune response should be an important life-history trait as parasitism can impact upon an individual's fecundity and survival prospects, and hence its fitness. However, immune function is likely to be costly as resources must be divided between many important traits. Whilst many studies have examined host resistance to particular parasite types, fewer have considered general immune responses. Studies that have considered general immune responses tend to do so in vertebrate models. However, the complexity of the vertebrate immune system makes the examination of evolutionary aspects of immune function difficult. Using larvae of the genus Spodoptera (Lepidoptera: Noctuidae) as a model system, this study examines' genetic and phenotypic aspects of innate immunity. The aims were to assess the levels of additive genetic variation maintained in immune traits, to consider possible costs that could maintain this variation, and to assess the role of phenotypic plasticity in ameliorating those costs. A key finding of this study was that high levels of additive genetic variation were maintained in all of the measured Immune traits. Analysis of the genetic correlations between traits revealed potential trade-offs within the immune system and between immune components and body condition. In addition, it was shown that larvae living at high densities invest more in immune function than those living in solitary conditions, suggesting that larvae can minimise the costs of immune function by employing them only when the risk of pathogenesis is high.

The need for new anti- TB drugs is increasingly rising because of the resistance of M. tuberculosis to existing drugs. The mycobacterial cell wall serves as an impermeable protective barrier for the bacilli from toxins and chemotherapeutic agents, mainly due to the mycolic acids waxy outer layer. The mycolic acids play an important role in the architecture and physical properties of the mycobacterial cell wall. This study was based on the observed mimicry and association between the host cholesterol and the mycolic acids. This may present yet another way in which the TB bacilli survives by manipulating its host and using some of its components for its survival. The research focused on whether the cholesterol-like molecules on the mycobacterial cell surface can be targeted for effective delivery of anti-mycobacterial agents. In order to exploit the ability of M tuberculosis to accumulate cholesterol or interact with it, a cholesterol¬binding molecule was used for targeting an anti- TB drug to the mycobacterial cell wall or to the cell membrane of infected macrophages. It was observed that the drug does possess anti-mycobacterial activities even though higher concentrations of the compound were required. This supports the idea that the ability of cholesterol to interact with the mycobacterial mycolic acids can be exploited for designing of anti- TB agents. It was also demonstrated in this study that cholesterol has a negative effect on the activity of INH. Thus cholesterol, which is required for entry and survival of M tuberculosis in the host cells, has yet another protective effect on this pathogen. The possible ability of cholesterol to target the same enzyme(s) as INH is another small piece of knowledge to complete the puzzle to understanding the mode of virulence and pathogenesis of this pathogen and develop of new ways to fight the old enemy. / Dissertation (MSc(Biochemistry))--University of Pretoria, 2006. / Biochemistry / unrestricted

No description available.

Tuberculosis has returned with vengeance mainly due to the resurgence of multi drug resistant strains incurred by non-compliance to the 6-9 months chemotherapy programme. Co-infection with HIV, which disorientates the immune response, has aggravated the situation. This study was built on previous observations that indicated that the major lipid cell wall component of M. tuberculosis, i.e. mycolic acids, a wax that envelopes and protects the bacillus from the hostile host immune system, can be purified and administered to animals for protection against subsequent tuberculosis induction. It was established in this study that mycolic acids pre-treatment can significantly protect mice upon subsequent intranasal infection with M. tuberculosis and that this protection is not attributed so much to the T helper cell immunity, but rather through induction of innate immunity. In the murine AIDS model, innate immunity induced by mycolic acids pre-treatment was not enough to protect the virally immunocompromised mice against subsequent M. tuberculosis infection. Mycolic acids administration in mice did not support tuberculosis chemotherapy to enable shortening of the duration of chemotherapy. In human tuberculosis patients, antibodies to mycolic acids could be measured in a specially adapted configuration of a resonant mirror biosensor. The preliminary investigation opened up the possibility that the prevalence of anti-mycolic acids antibodies in tuberculosis patients may be measured as a surrogate marker for tuberculosis infection. An apparent cross-reactivity between mycolic acids and cholesterol in binding to tuberculosis patient antibodies may provide far reaching insight in the role of the mycolic acids in the cell wall to facilitate infection. This research contributed significantly to the understanding of the host-pathogen interaction in tuberculosis, to open up fresh approaches to improved diagnosis and chemotherapy. / Thesis (DPhil (Biochemistry))--University of Pretoria, 2006. / Biochemistry / unrestricted

No description available.

Cerithidea california is examined to determine the fecundity of the parasitic trematode species in its gonad. Five species of trematodes are studied (Cloacitrema michiganensis, Euhaplorchis californiensis, Parorchis acanthus, Himasthia rhigedana, and Acanthoraryphium sp.). Their fecundity is determined by direct counts of rediae and estimation of the cercarial population. Correlations are shown for trematode numbers and snail size. Incidences of infection are given with regard to site, snail size, and trematode species. Comparison is made between infection ratios of C. californica and another marsh snail, Batillaria zonalis.

No description available.