SUMMARY OF RESEARCH DOCUMENTS ON CRYPTOSPORIDIUM AND GIARDIA ABSTRACTED BETWEEN 1995 AND 1997
The following is a summary of research papers on Cryptosporidium and Giardia which have been published between the beginning of 1995 and the present date. The papers have been summarised in broad subject areas and the full references are given after the text. Part of the summary is taken from abstracts prepared for a conference in California and in some cases, data was not presented in the abstract.
A portion of the work is centered around water treatment, in particular the optimisation of existing coagulation and flocculation practices. Novel treatments such as ultra-filtration and nano-filtration also appear. Disinfection studies have looked at combinations of disinfectants to obtain synergistic effects and the application of new technologies such as mixed oxidant species and ultra-violet light (UV). A variety of viability assays are available from mouse infectivity, tissue culture, excystation and dye exclusion. Of all of these perhaps tissue culture may be a valuable technique for the future. A number of outbreaks have been documented and a proportion of these involve swimming pools. Distributions of cysts and oocysts in surface waters, groundwaters, sewage effluents and slurries have been studied and in particular efforts have been made to collect data other than through routine sampling programmes. It is not always possible to know when oocysts are present in high numbers but efforts should be made to collect data when environmental conditions suggest raw water quality deterioration. In addition a clear understanding of the likely input of parasites to a raw water catchment is helpful.
Methods for detection continue to improve. Many authors highlight the need to understand recovery efficiencies and the factors that can lead to poor recoveries. Perhaps collation of this data might be useful as a ‘How to improve your analysis’ guide. Emphasis for the most part is on simplicity with reproducibility and the need for quality control. There are many variables in any detection method but it is more important that a laboratory knows what its variables are rather than the method it chooses. Better concentration techniques, the use of immunomagnetic separation (IMS) and flow cytometry have all helped improve detection and reduce analytical time. Determination of viability by tissue culture is an interesting development. The viability of a single oocyst can be determined from replication of sporozoites. Detection may be by means of enzyme-linked immunosorbent assay (ELISA) or using molecular techniques with viability assay times ranging from 24-48 hours. Molecular techniques are based on either DNA or RNA amplification or fluorescent in-situ hybridisation (FISH). These techniques also demonstrate potential viability and infectivity. The Standing Committee of Analysts and the United States Environment Protection Agency both have draft revised methods for the analysis of water samples. These are being completed at this time and should be available in the near future. The rate of progress with development will probably mean that they will be out of date before too long.
Studies of survival in the environment continue to demonstrate that whilst Giardia is a poor survivor, Cryptosporidium can survive well although aged oocysts are more susceptible to environmental factors and the effects of disinfectants.Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.