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Title: Cryptosporidium sp. oocysts in the aquatic environment : occurrence, removal and destruction
Author: Parker, Jeremy Francois William
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1993
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In the past 10 years the protozoan parasites Cryptosporidium and Giardia have been recognised as important gastrointestinal pathogens of man. Both parasites have been responsible for numerous outbreaks of waterborne diarrhoeal disease in humans. Methods developed for the recovery and detection of these organisms in water and water-related samples involve the filtration of large volumes of water (100 - 1000 L), the elution and concentration of the transmissive stage and their detection using immunofluorescent antibody techniques. During the course of this study Cryptosporidium sp. oocysts and Giardia sp. cysts were detected in surface water at ranges of 0.006 - 15.6 oocysts/L and 0.009 - 2.1 cysts/L respectively, in treated water at ranges of 0.008 - 1.36 oocyst/L and 0.007 - 0.34 cyst/L respectively. In raw sewage, the concentrations ranged from 2.5-75 oocysts/L and 242.5 - 792.5 cysts/L and, in treated sewage effluent, from 0.024 - 26.5 oocysts/L and 0.095 - 361.7 cysts/L. Removal of these organisms by water treatment processes such as slow sand filtration, rapid sand filtration and microstraining ranged from 62% to 92% and removal by sewage treatment processes ranged from 79.6% to 99.3%. Cryptosporidium sp. oocysts were detected in water at the abstraction point of an upland water supply and in potable water in the distribution network. Information available on human cryptosporidiosis in the communities served by this water supply indicated that the small numbers of oocysts detected in both raw and final water could not be correlated with any identifiable outbreak of waterborne disease. The majority of oocysts detected at the abstraction point were non-viable. Oocysts were detected in human sewage effluent and bovine faecal specimens, implicating both as a source of contamination of tributaries to the loch from which water was abstracted. Immunomagnetic separation techniques were used to improve the recovery of oocysts during sample processing and to recover oocysts in order to assess their viability. Recoveries of 33% to 66% were achieved from environmental samples. Ozone was used successfully to inactivate Cryptosporidium parvum oocysts, with 100% inactivation achieved at ozone concentrations of 3 and 5 mg/L for between 2 and 10 min at pH 5, 7 and 9 at temperatures of 5°C and 20°C. Shaking oocysts with sand for time periods between 5 and 90 min inactivated 50% to 99.7% of the oocysts. Exposing oocysts to 1 mg/L chlorine for 5 min after 5 min treatment with sand gave a further 15% inactivation. Oocysts are many times more resistant to disinfectants, including ozone, than other pathogens encountered in water treatment. Ozone produces oxidants such as superoxide ions during its decomposition. The antioxidant enzyme superoxide dismutase was detected in freeze-thawed fractions of oocysts at 5.44 to 9.27 U/mg protein. This may provide the parasite with a mechanism which can neutralise immune and non-immune oxidant mediated attack both during its development within the host and its exposure to disinfectants in water treatment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available