Differentiation of Cryptosporidium parvum isolates by a simplified randomly amplified polymorphic DNA technique

Detection of Cryptosporidium spp. and Giardia spp. in Environmental Water Samples: A Journey into the Past and New Perspectives

Among the major issues linked with producing safe water for consumption is the presence of the parasitic protozoa Cryptosporidium spp. and Giardia spp. Since they are both responsible for gastrointestinal illnesses that can be waterborne, their monitoring is crucial, especially in water sources feeding treatment plants. Although their discovery was made in the early 1900s and even before, it was only in 1999 that the U.S. Environmental Protection Agency (EPA) published a standardized protocol for the detection of these parasites, modified and named today the U.S. EPA 1623.1 Method. It involves the flow-through filtration of a large volume of the water of interest, the elution of the biological material retained on the filter, the purification of the (oo)cysts, and the detection by immunofluorescence of the target parasites. Since the 1990s, several molecular-biology-based techniques were also developed to detect Cryptosporidium and Giardia cells from environmental or clinical samples. The application of U.S. EPA 1623.1 as well as numerous biomolecular methods are reviewed in this article, and their advantages and disadvantages are discussed guiding the readers, such as graduate students, researchers, drinking water managers, epidemiologists, and public health specialists, through the ever-expanding number of techniques available in the literature for the detection of Cryptosporidium spp. and Giardia spp. in water.

Biology, persistence and detection of Cryptosporidium parvum and Cryptosporidium hominis oocyst

Cryptosporidium parvum and Cryptosporidium hominis are obligate enteric protozoan parasites which infect the gastrointestinal tract of animals and humans. The mechanism(s) by which these parasites cause gastrointestinal distress in their hosts is not well understood. The risk of waterborne transmission of Cryptosporidium is a serious global issue in drinking water safety. Oocysts from these organisms are extremely robust, prevalent in source water supplies and capable of surviving in the environment for extended periods of time. Resistance to conventional water treatment by chlorination, lack of correlation with biological indicator microorganisms and the absence of adequate methods to detect the presence of infectious oocysts necessitates the development of consistent and effective means of parasite removal from the water supply. Additional research into improving water treatment and sewage treatment practices is needed, particularly in testing the efficiency of ozone in oocyst inactivation. Timely and efficient detection of infectious C. parvum and C. hominis oocysts in environmental samples requires the development of rapid and sensitive techniques for the concentration, purification and detection of these parasites. A major factor confounding proper detection remains the inability to adequately and efficiently concentrate oocysts from environmental samples, while limiting the presence of extraneous materials. Molecular-based techniques are the most promising methods for the sensitive and accurate detection of C. parvum and C. hominis. With the availability of numerous target sequences, RT-PCR will likely emerge as an important method to assess oocyst viability. In addition, a multiplex PCR for the simultaneous detection of C. parvum, C. hominis and other waterborne pathogens such as Giardia lamblia would greatly benefit the water industry and protect human health.

Detection and differentiation of Cryptosporidium parasites that are pathogenic for humans by real-time PCR

Cryptosporidiosis is a significant cause of food-borne and waterborne outbreaks of diarrheal diseases. To better understand the route of transmission of Cryptosporidium parasites, a number of genotyping techniques have been developed, based on PCR-restriction fragment length polymorphism or sequencing analysis of antigen, structural, and housekeeping genes. In this study, a real-time assay for the detection of Cryptosporidium oocysts is described. This technique had a detection limit of five oocysts. By melting curve analysis of PCR products with fluorescence-labeled hybridization probes, this technique was able to differentiate five common Cryptosporidium parasites that are pathogenic for humans in a single PCR. We evaluated and validated the test using samples from presently known Cryptosporidium parasites that are pathogenic for humans. This technique provides an alternative molecular tool in epidemiologic studies of human cryptosporidiosis.

Genotyping Cryptosporidium parvum with an hsp70 single-nucleotide polymorphism microarray

We investigated the application of an oligonucleotide microarray to (i) specifically detect Cryptosporidium spp., (ii) differentiate between closely related C. parvum isolates and Cryptosporidium species, and (iii) differentiate between principle genotypes known to infect humans. A microarray of 68 capture probes targeting seven single-nucleotide polymorphisms (SNPs) within a 190-bp region of the hsp70 gene of Cryptosporidium parvum was constructed. Labeled hsp70 targets were generated by PCR with biotin- or Cy3-labeled primers. Hybridization conditions were optimized for hybridization time, temperature, and salt concentration. Two genotype I C. parvum isolates (TU502 and UG502), two C. parvum genotype II isolates (Iowa and GCH1), and DNAs from 22 non-Cryptosporidium sp. organisms were used to test method specificity. Only DNAs from C. parvum isolates produced labeled amplicons that could be hybridized to and detected on the array. Hybridization patterns between genotypes were visually distinct, but identification of SNPs required statistical analysis of the signal intensity data. The results indicated that correct mismatch discrimination could be achieved for all seven SNPs for the UG502 isolate, five of seven SNPs for the TU502 isolate, and six of seven SNPs for both the Iowa and GCH1 isolates. Even without perfect mismatch discrimination, the microarray method unambiguously distinguished between genotype I and genotype II isolates and demonstrated the potential to differentiate between other isolates and species on a single microarray. This method may provide a powerful new tool for water utilities and public health officials for assessing point and nonpoint source contamination of water supplies.

Epidemiology of Cryptosporidium: transmission, detection and identification

There are 10 valid species of Cryptosporidium and perhaps other cryptic species hidden under the umbrella of Cryptosporidium parvum. The oocyst stage is of primary importance for the dispersal, survival, and infectivity of the parasite and is of major importance for detection and identification. Because most oocysts measure 4-6 microm, appear nearly spherical, and have obscure internal structures, there are few or no morphometric features to differentiate species and in vitro cultivation does not provide differential data as for bacteria. Consequently, we rely on a combination of data from three tools: morphometrics, molecular techniques, and host specificity. Of 152 species of mammals reported to be infected with C. parvum or an indistinguishable organism, very few oocysts have ever been examined using more than one of these tools. This paper reviews the valid species of Cryptosporidium, their hosts and morphometrics; the reported hosts for the human pathogen, C. parvum; the mechanisms of transmission; the drinking water, recreational water, and food-borne outbreaks resulting from infection with C. parvum; and the microscopic, immunological, and molecular methods used to detect and identify species and genotypes.

Immunomagnetic separation of Cryptosporidium parvum oocysts using MACS MicroBeads and high gradient separation columns

We evaluated the MACS immunomagnetic separation (IMS) system for concentrating Cryptosporidium parvum. Oocysts were first labeled with fluorescein isothiocyanate (FITC) or rabbit anti-C. parvum antibodies, then linked to MicroBeads coated with anti-FITC or anti-rabbit IgG, and separated through a high gradient separation column. Results indicated that over 95% of oocysts were recovered and their fluorescence and infectivity were retained. The presence of MicroBeads showed no effect on genomic DNA extraction and subsequent polymerase chain reaction (PCR)-based analyses, as sensitivity of PCR (10 oocysts) and the band pattern of randomly amplified polymorphic DNA (RAPD) were identical to those using DNAs extracted from normally purified oocysts. IMS-PCR consistently detected as few as 10 oocysts from 100 ml of apple juice or homogenized milk and IMS-IFA could detect 100 oocysts from 1 g of deer manure, demonstrating the efficiency of IMS in recovering oocysts from environmental and food samples. Our results suggest that the MACS IMS system could be used for multiple applications in Cryptosporidium research.

Variation in Cryptosporidium: towards a taxonomic revision of the genus

Cryptosporidium is an important cause of enteric disease in humans and other animals. Limitations associated with conventional diagnostic methods for cryptosporidiosis based on morphological features, coupled with the difficulty of characterising parasites isolated in the laboratory, have restricted our ability to clearly identify species. The application of sensitive molecular approaches has obviated the necessity for laboratory amplification. Such studies have found considerable evidence of genetic heterogeneity among isolates of Cryptosporidium from different species of vertebrate, and there is now mounting evidence suggesting that a series of host-adapted genotypes/strains/species of the parasite exist. In this article, studies on the molecular characterisation of Cryptosporidium during the last 5 years are reviewed and put into perspective with the past and present taxonomy of the genus. The predictive value of achieving a sound taxonomy for the genus Cryptosporidium with respect to understanding its epidemiology and transmission and controlling outbreaks of the disease is also discussed.

Rapid DNA extraction methods and new primers for randomly amplified polymorphic DNA analysis of Giardia duodenalis

A randomly amplified polymorphic DNA (RAPD) procedure using simple genomic DNA preparation methods and newly designed primers was optimized for analyzing Giardia duodenalis strains. Genomic DNA was extracted from in vitro cultivated trophozoites by five freezing-thawing cycles or by sonic treatment. Compared to a conventional method involving proteinase K digestion and phenol extraction, both freezing-thawing and sonication were equally efficient, yet with the advantage of being much less time- and labor-intensive. Five of the 10 tested RAPD primers produced reproducible polymorphisms among five human origin G. duodenalis strains, and grouping of these strains based on RAPD profiles was in agreement among these primers. The consistent classification of two standard laboratory reference strains, Portland-1 and WB, in the same group confirmed previous results using other fingerprinting methods, indicating that the reported simple DNA extraction methods and the selected primers are useful in RAPD for molecular characterization of G. duodenalis strains.