Spironucleus is an opportunistic protozoan parasite capable of causing devastating losses in the production of both ornamental and food fish. Control of infection outbreaks is problematic due to restrictions on the use of chemotherapeutics and rapid parasite transmission amongst fish. This PhD investigated the life cycle, biochemistry and chemotherapy of Spironucleus vortens. Direct transmission of S. vortens was found to be facilitated by the trophozoite form, information which may be applied in aquaculture to prevent infection outbreaks. No S. vortens cysts were observed in vitro or in vivo and trophozoites were able to survive for prolonged periods in the faeces of angelfish. This novel finding facilitated development of a non-invasive method to quantify the degree of intestinal colonization in the host, which was then applied to determine the efficacy of new and existing chemotherapeutics against S. vortens in vivo. Garlic-derived compounds were shown to be realistic alternatives to the current drug of choice, metronidazole, in the treatment of Spironucleosis in fish. Synergy between metronidazole and the garlic-derived compound, ajoene, was also observed in vitro and in vivo. The mode of action of metronidazole and garlic-derivatives involved disruption of S. vortens intracellular redox balance, a pivotal cellular process which ensures normal cellular function and survival. Further biochemical investigations into the antioxidant defence system (consisting of glutathione, thioredoxin and superoxide dismutase) as well as the carbohydrate and amino acid metabolism of S. vortens provided greater understanding of the success of this organism as a parasite. This is reflected in its ability to withstand fluctuations in O2 and nutrition during key pathogenic stages of its life cycle, including extra-intestinal systemic infection and transmission to a new host.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:571758 |
| Date | January 2013 |
| Creators | Williams, Catrin Ffion |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/47574/ |
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