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Deposition and adhesion of Cryptosporidium oocysts on surfaces

Pugh, Hedley James; (1995) Deposition and adhesion of Cryptosporidium oocysts on surfaces. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Cryptosporidium is a small protozoan parasite which is widespread in the environment where it exists as a spherical oocyst typically 4-5 μm in diameter. An extensive review of the literature indicates that there has been a number of well documented waterborne outbreaks of cryptosporidiosis, the disease caused by the parasite. It is also apparent that little is known of the effectiveness of standard water treatment processes for the removal of the organism. Filtration, commonly used in water treatment, appears to be effective although there is no fundamental information on the factors affecting the adhesion of Cryptosporidium oocysts to sand grains (a common filter media). Three complementary techniques have been used to study the adhesion of oocysts to planar surfaces and granular filter media: (i) A fundamental micropipette technique whereby the force of adhesion of an individual oocyst to a microscope cover glass is measured directly with a flexible micropipette. (ii) A laminar flow technique whereby oocysts that have settled in a cell are subject to increasing flow rates and the degree of removal observed directly by microscope. The strength of attachment is indicated by the flow rate necessary to detach adhering oocysts. The corresponding shear can be calculated and hence the force required to remove an oocyst. (iii) The removal of oocysts by filtration through packed beds has been studied by a chromatographic technique, in which the removal rate is determined by a specially developed particle monitor. Experiments were conducted in solutions of calcium and sodium nitrate and ultra-pure water with a number of surface treatments. Factors influencing the adhesion of oocysts included: (i) Time of contact with the surface. (ii) Solution chemistry (iii) Modification of surface characteristics (iv) The presence of extracelluar polymers. These effects and possible explanations are fully discussed.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Deposition and adhesion of Cryptosporidium oocysts on surfaces
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Biological sciences; Adhesion; Cryptosporidium oocysts; Deposition
URI: https://discovery.ucl.ac.uk/id/eprint/10104442
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