Citation:

BUKHARI, Z., D. M. HOLT, M. W. WARE, AND F. W. SCHAEFER. EVALUATING IN VITRO INFECTIVITY FOR MEASURING UV DISINFECTION OF CRYPTOSPORIDIUM PARVUM OOCYSTS IN FINISHED WATER. Presented at Water Quality Technology Conference, Quebec, QC, CANADA, November 06 - 10, 2005.

Impact/Purpose:

1) Refine new, practical methods for the detection of CCL-related and emerging waterborne human protozoa.

2) Perform field tests of devices or methods that have been developed under this task.

3) Evaluate these methods or devices in a variety of water matrices and parasite concentrations.

This work in this task supports CCL2 and 3 and is expected to be completed by 9/07.

Description:

UV technology to inactivate Cryptosporidium parvum oocysts has become well established in the US. The challenge now is to effectively demonstrate UV reactor performance and disinfection capacity with various finished water matrices and under different operational conditions. In such evaluations, surrogate organisms such as MS2 bacteriophage are finding acceptance in the US; however, it remains imperative that reactor validation studies continue to include parallel bench scale UV disinfection studies using C. parvum oocysts in finished water. In this manner, the impact of chemicals constituents, used in the abatement of taste and odor or in the enhancement of filtration and/or coagulation, on the effectiveness of UV light for inactivation of C. parvum oocysts can be monitored. With this information the appropriate applied UV dose needed to achieve a target disinfection credit can be determined.

Currently the neonatal mouse infectivity assays are considered the method of choice for measuring oocyst inactivation. These procedures require specialized animal experimentation licenses and animal care facilities and usually require 7 to 10 days to generate results. In addition to the time consuming nature of these procedures, the cost of animal experimentation makes their routine use prohibitive. Alternative methods, such as in vitro viability assays using fluorogenic vital dyes or in vitro excystation assays, perform poorly in predicting inactivation of C. parvum oocysts following UV disinfection. In addition, currently only anecdotal evidence exists for the effectiveness of in vitro infectivity assays in accurately predicting inactivation of UV treated C. parvum.

The utility of the in vitro infectivity assay was evaluated with "blind" spike doses of C. parvum oocysts that were enumerated by flow cytometry. At the American Water laboratories, these unknown spike doses of C. parvum oocysts were administered to a cell culture assay utilizing human adenocarcinoma (HCT-8) cells and were detected by immunofluorescence (IFA) microscopy. Data from these "blind" trials indicated that the optimized cell culture-IFA procedure yielded highly reproducible and accurate results, thereby confirming the findings reported by Bukhari and LeChevallier (2003). The next phase of these "blind" trials is to evaluate this assay for measuring the infectivity of UV treated C. parvum oocysts. The successful completion of these trials will help to ensure that a standardized procedure is available for the water industry to use as a tool for conducting UV disinfection studies on C. parvum oocysts suspended in different finished water matrices.

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