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MOLECULAR DETECTION OF CRYPTOSPORIDIUM OOCYSTS IN WATER: THE CHALLENGE AND PROMISE
Citation:
Xiao, L., A. Lal, AND M D. Royer*. MOLECULAR DETECTION OF CRYPTOSPORIDIUM OOCYSTS IN WATER: THE CHALLENGE AND PROMISE. Presented at 2002 AWWA Water Quality Technology Conference, Seattle, WA, 11/10-13/2002.
Description:
Because of the presence of host-adapted Cryptosporidium species and genotypes, molecular tools can help assess the source and hazardous potential of Cryptosporidium oocysts in water. The development and use of molecular tools in the analysis of environmental samples have gone though several phases. Earlier polymerase chain reaction (PCR) tools were designed for the detection of Cryptosporidium oocysts in clinical samples. Subsequently, a genotyping component was incorporated into many of these assays to differentiate Cryptosporidium occysts of anthroponotic origins from zoonotic origins. These tools were mostly based on sequences of bovine C. parvum isolates, and were intended for the detection for C. parvum in clinical samples, thus they do not detect and differentiate Cryptosporidium spp. and many distant C,. parvum genotypes. More recently, new molecular tools have broad specificity and the ability to differentiate Cryptosporidium species and genotype have been introduced whcih has resulted in the finding of five major Cryptosporidium parasites in humans: The C. parvum human and bovine genotypes, C. meleagridis, C. felis, and C. canis. Current problems in molecular detection of Cryptosporidium oocysts include: (1) the availability of only a limited number of tools for species differentiation, most of which are based on the small subunit rRNA gene; (2) the nonspecificity of some species differentiation tools; (3) the misinterpretation of data because of outdated knowledge of the evolving research field; and (4) the existence of erroneous data in the database and publications. Nevertheless, in conjunction with immunomagnetic separation (IMS), some PCR-based tools have been successfully used in the detection, differentiation, and tracking of Cryptosporidium oocysts in stormwater, surface water, and wastewater. Results of these studies have shown that a significant proportion of cryptosporidium occysts in water do not have high human-infective potential which would have been overestimated by the recommended ICR method or method 1622/1623. Despite the recent success, much more needs to be done before molecular tools can be used in routine analysis of water samples. Specifically, (1) rigorous standardization and testing have yet to be carried out in order to develop quality assurance and quality control procedures; (2) there is a need for the development of protocols that allow the extraction of PCR-quality DNA without using the expensive and pathogen-specific IMS; (3) turnaround times have to be reduced to allow close to real-time detection; (4) quantitative and high resolution typing procedures need to be incorporated for analysis of samples in special situations (such as outbreaks or bioterrorism); and (5) there is a need to take advantage of new techniques such as biosensors and microarrays. The use of molecular tools can potentially generte data that are useful in the risk assessment of various waters in different environmental settings and for watershed management and source water protection.