Survival of Cryptosporidium parvum oocysts under various environmental pressures

Modelling the sewage discharge and dispersion of Cryptosporidium and Giardia in surface water

Modelling the discharge of parasitic protozoa into surface water and the dispersion in rivers and streams gives insight into the contribution of the different sources of environmental contamination and in the transmission of these organisms from the point of discharge to drinking water abstraction points and bathing sites. We tested the applicability of emission (PROMISE) and dispersion (WATNAT) models developed for chemical pollutants to describe the environmental behaviour of Cryptosporidium and Giardia in the Netherlands. The annual load of Cryptosporidium and Giardia in domestic wastewater was 3.2 x 10(13) and 3.8 x 10(14) respectively. The majority (85%) of the Cryptosporidium oocysts was discharged with effluent of wastewater treatment plants. while the majority (82%) of the Giardia cysts was discharged with untreated wastewater discharges and sewer overflows. The estimated annual import through the river Rhine and Meuse was 3.2 x 1014 Cryptosporidium oocysts and 2.1 x 10(15) Giardia cysts, of which the river Rhine contributed 87 and 66%, respectively. This outweighed the total load of the discharges of treated and untreated wastewater in the Netherlands. The combination of PROMISE and WATNAT predicted concentrations of Cryptosporidium and Giardia in surface water that were in the same order of magnitude as the concentrations that were observed at 5 of the 6 sites compared. At a site with primarily agricultural contamination, the models predicted concentrations that were 1 10log-unit lower than the observed concentrations. This is a first step in the direction of a quantitative description of the transmission cycle of Cryptosporidum and Giardia through water. The use of these models combines observational occurrence data and experimental data from laboratory survival studies into a single integrated description. The description needs further improvement by incorporation of agricultural run-off and increasing the number and time frame of input monitoring data.

Effects of combined water potential and temperature stresses on Cryptosporidium parvum oocysts

Hosts infected with the parasite Cryptosporidium parvum may excrete oocysts on soils in watersheds that supply public drinking water. Environmental stresses decrease the numbers of oocysts after deposition on soils. However, the rates and effects of combined stresses have not been well characterized, especially for the purposes of estimating decrease in numbers. We subjected oocysts to combined stresses of water potential (-4, -12, and -33 bars), above-freezing temperatures (4 and 30 degrees C), and a subfreezing temperature (-14 degrees C) for 1, 14, and 29 days and one to six freeze-thaw cycles (-14 to 10 degrees C) to estimate coefficients to characterize population degradation using multiplicative error and exponential decay models. The experiments were carried out in NaCl solutions with water potentials of -4, -12, and -33 bars, in combination with temperature stresses at levels that could be expected in natural soils. Increased water potential increased the rate of population degradation for all temperature conditions investigated. Enhanced degradation leads to estimated rates of population degradation that are greater than those that have been reported and used in previous studies conducted to assess risk of water supply contamination from sources of C. parvum.

Transport and fate of Cryptosporidium parvum oocysts in intermittent sand filters

The transport potential of Cryptosporidiim parvum (C. parvum) through intermittent. unsaturated, sand filters used for water and wastewater treatment was investigated using a duplicated. 2(3) factorial design experiment performed in bench-scale, sand columns. Sixteen columns (dia = 15 cm, L = 61 cm) were dosed eight times daily for up to 61 days with 65,000 C. parvum oocysts per liter at 15 degrees C. The effects of water quality, media grain size, and hydraulic loading rates were examined. Effluent samples were tested for pH, turbidity, and oocyst content. C. parvum effluent concentrations were determined by staining oocysts on polycarbonate filters and enumerating using epifluorescent microscopy. At completion, the columns were dismantled and sand samples were taken at discrete depths within the columns. These samples were washed in a surfactant solution and the oocysts were enumerated using immunomagnetic separation techniques. The fine-grained sand columns (d50 = 0.31 mm) effectively removed oocysts under the variety of conditions examined with low concentrations of oocysts infrequently detected in the effluent. Coarse-grained media columns (d = 1.40 mm) yielded larger numbers of oocysts which were commonly observed in the effluent regardless of operating conditions. Factorial design analysis indicated that grain size was the variable which most affected the oocyst effluent concentrations in these intermittent filters. Loading rate had a significant effect when coarse-grained media was used and lesser effect with fine-grained media while the effect of feed composition was inconclusive. No correlations between turbidity, pH, and effluent oocyst concentrations were found. Pore-sizc calculations indicated that adequate space for oocyst transport existed in the filters. It was therefore concluded that processes other than physical straining mechanisms are mainly responsible for the removal of C. pavum oocysts from aqueous fluids in intermittent sand filters used under the conditions Studied in this research.

Infectivity of Cryptosporidium parvum oocysts following cryopreservation

This study was undertaken to investigate the cryopreservation of Cryptosporidium parvum oocysts. Oocysts purified from mouse feces were suspended in distilled water, 10% glycerin, and 2.5% potassium dichromate. They were stored at -20 C and -80 C for 2, 7, and 30 days, respectively. In addition to the purified oocysts, the feces of C. parvum-infected mice were preserved under the same conditions described above. Purified and fecal oocysts were thawed at 4 C, and their viability was assessed by a nucleic acid stain, excystation test, tissue culture infectivity test, and infectivity to immunosuppressed adult mice. Oocysts purified from fecal material prior to cryopreservation lost most of their viability and all of their infectivity for tissue culture and mice. However, when oocysts were cryopreserved in feces, between 11.7 and 34.0% were judged to be viable and retained their infectivity for mice when stored at -20 C (but not -80 C) for 2, 7, and 30 days. Clearly, fecal material provides a cryoprotective environment for C. parvum oocysts stored at -20 C for at least 30 days.

Chlorine dioxide inactivation of Cryptosporidium parvum oocysts and bacterial spore indicators

Cryptosporidium parvum, which is resistant to chlorine concentrations typically used in water treatment, is recognized as a significant waterborne pathogen. Recent studies have demonstrated that chlorine dioxide is a more efficient disinfectant than free chlorine against Cryptosporidium oocysts. It is not known, however, if oocysts from different suppliers are equally sensitive to chlorine dioxide. This study used both a most-probable-number-cell culture infectivity assay and in vitro excystation to evaluate chlorine dioxide inactivation kinetics in laboratory water at pH 8 and 21 degrees C. The two viability methods produced significantly different results (P < 0.05). Products of disinfectant concentration and contact time (Ct values) of 1,000 mg. min/liter were needed to inactivate approximately 0.5 log(10) and 2.0 log(10) units (99% inactivation) of C. parvum as measured by in vitro excystation and cell infectivity, respectively, suggesting that excystation is not an adequate viability assay. Purified oocysts originating from three different suppliers were evaluated and showed marked differences with respect to their resistance to inactivation when using chlorine dioxide. Ct values of 75, 550, and 1,000 mg. min/liter were required to achieve approximately 2.0 log(10) units of inactivation with oocysts from different sources. Finally, the study compared the relationship between easily measured indicators, including Bacillus subtilis (aerobic) spores and Clostridium sporogenes (anaerobic) spores, and C. parvum oocysts. The bacterial spores were found to be more sensitive to chlorine dioxide than C. parvum oocysts and therefore could not be used as direct indicators of C. parvum inactivation for this disinfectant. In conclusion, it is suggested that future studies address issues such as oocyst purification protocols and the genetic diversity of C. parvum, since these factors might affect oocyst disinfection sensitivity.

Effect of high-rate algal ponds on viability of Cryptosporidium parvum oocysts

The physicochemical conditions of high-rate algal ponds were responsible for a more than 97% reduction in the infectivity of Cryptosporidium parvum oocysts in neonatal mice. The use of semipermeable bags of cellulose showed that pH, ammonia, and/or light seems to be a major factor for the inactivation of oocysts in wastewater, supporting the importance of alga-based systems for safer reuse of treated wastewater.

The emerging nosocomial pathogens Cryptosporidium, Escherichia coli O157:H7, Helicobacter pylori, and hepatitis C: epidemiology, environmental survival, efficacy of disinfection, and control measures

New and emerging infectious diseases pose a threat to public health and may be responsible for nosocomial outbreaks. Cryptosporidium parvum and Escherichia coli are gastrointestinal pathogens that have caused nosocomial infections via person-to-person transmission, environmental contamination, or contaminated water or food. Helicobacter pylori has been transmitted via inadequately disinfected endoscopes. Finally, hepatitis C may be acquired by healthcare personnel by percutaneous or mucous membrane exposure to blood or between patients by use of contaminated blood products or via environmental contamination. Rigorous adherence to Standard Precautions, Contact Precautions for patients with infectious diarrhea, disinfection of environmental surfaces, and appropriate disinfection of endoscopes are adequate to prevent nosocomial acquisition of these pathogens.

Microbiological safety of drinking water

Emerging pathogens in drinking water have become increasingly important during the decade. These include newly-recognized pathogens from fecal sources such as Cryptosporidium parvum, Campylobacter spp., and rotavirus, as well as pathogens that are able to grow in water distribution systems, like Legionella spp., mycobacteria, and aeromonads. To perform a risk analysis for the pathogens in drinking water, it is necessary to understand the ecology of these organisms. The ecology of the drinking-water distribution system has to be evaluated in detail, especially the diversity and physiological properties of water bacteria. The interactions between water bacteria and (potential) pathogens in such diverse habitats as free water and biofilms are essential for the survival or growth of hygienically relevant organisms in drinking water. Results of epidemiological studies together with ecological data are the basis for effective resource protection, water treatment, and risk assessment.

Cryptosporidiosis. A global challenge

During the last 30 years, our concept of cryptosporidiosis has changed from that of a rare, largely asymptomatic disease, to an important cause of diarrhea in animals and humans worldwide. Significant disease first appeared in cattle. Subsequently, the zoonotic danger of the organism was recognized in HIV-infected persons and young children. Cryptosporidium are now ubiquitous and disease has been described in over 79 host species. Cryptosporidiosis has become a major cause of calfhood diarrhea worldwide. In humans it accounts for up to 20% of all cases of childhood diarrhea in developing countries and is a potentially fatal complication of AIDS. Waterborne contamination is a growing concern as a source of widespread outbreaks of disease. Factors that have contributed to the emergence of cryptosporidiosis in animals include biological features of the organism, the lack of an effective treatment or preventative, increased environmental contamination, and trends in livestock production. In humans the zoonotic nature of infection and an increased at-risk population have contributed to disease. Genetic characterization of Cryptosporidium, improved detection methods, and a better understanding of the factors that predispose to disease are important contributions to understanding the epidemiology of cryptosporidiosis.

Detection of Cryptosporidium oocysts in soil samples by enzyme-linked immunoassay

An ELISA protocol was adapted for detection of Cryptosporidium parvum oocysts in soil samples and the limit of detection of the test was determined. A modified indirect antigen capture ELISA protocol was developed using monoclonal antibodies against the oocyst outer wall. The accuracy of the ELISA was compared to spiked soil samples and measured in terms of sensitivity and specificity of the test. The performance of the ELISA was evaluated in field soil samples and measured using the kappa-statistics. Similarly, the performance of the ELISA was compared to the concentration flotation method, to a modified concentration flotation method and to a commercial ELISA (ProSpecT) in field fecal and soil samples. The limit of detection of the test was selected to be 10,000 oocysts/g. At this limit of detection, the ELISA had a sensitivity of 95% and specificity of 100%. The agreement between the ELISA and the modified flotation-concentration method in detecting Cryptosporidium oocysts in soil samples was 32% (kappa=0.32). The ELISA had the same relative sensitivity (82%) in comparison to both the flotation and ProSpecT in determining Cryptosporidium-infection status of an animal. The kappa-statistics was 0.26 for both tests. The developed ELISA proved to be a valuable diagnostic test for detecting oocysts in soil samples and has a potential application in determining the infection status of animals.

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.

An immunoglobulin G1 monoclonal antibody highly specific to the wall of Cryptosporidium oocysts

The detection of Cryptosporidium oocysts in drinking water is critically dependent on the quality of immunofluorescent reagents. Experiments were performed to develop a method for producing highly specific antibodies to Cryptosporidium oocysts that can be used for water testing. BALB/c mice were immunized with six different antigen preparations and monitored for immunoglobulin G (IgG) and IgM responses to the surface of Cryptosporidium oocysts. One group of mice received purified oocyst walls, a second group received a soluble protein preparation extracted from the outside of the oocyst wall, and the third group received whole inactivated oocysts. Three additional groups were immunized with sequentially prepared oocyst extracts to provide for a comparison of the immune response. Mice injected with the soluble protein extract demonstrated an IgG response to oocysts surface that was not seen in the whole-oocyst group. Mice injected with whole oocysts showed an IgM response only, while mice injected with purified oocyst walls showed little increase in IgM or IgG levels. Of the additional reported preparations only one, BME (2-mercaptoethanol treated), produced a weak IgM response to the oocyst wall. A mouse from the soluble oocyst extract group yielding a high IgG response was utilized to produce a highly specific IgG(1) monoclonal antibody (Cry104) specific to the oocyst surface. Comparative flow cytometric analysis indicated that Cry104 has a higher avidity and specificity to oocysts in water concentrates than other commercially available antibodies.

Effect of high hydrostatic pressure on Cryptosporidium parvum infectivity

The incidence of foodborne disease outbreaks caused by contaminated low-pH fruit juices is increasing. With recent mandatory pasteurization of apple juice and the industry's concerns of food safety, fruit juice processors are showing more interest in alternative nonthermal technologies that can kill >99.99% of microbial pathogens present in foods. The association of the coccidian protozoan, Cryptosporidium, with diarrheal disease outbreaks from contaminated tap water and fruit juice raises a safety concern in the food and beverage industries. The objective of this study was to evaluate the effects of high hydrostatic pressure (HHP) on C. parvum oocysts. Oocysts were suspended in apple and orange juice and HHP treated at 5.5 x 10(8) Pa (80,000 psi) for 0, 30, 45, 60, 90, and 120 s. Oocyst viability was assessed by excystation using bile salts and trypsin while the cell culture foci detection method was used to assess infectivity. Results indicated that HHP inactivated C. parvum oocysts by at least 3.4 log10 after 30 s of treatment. No infectivity was detected in samples exposed to > or =60 s of HHP and >99.995% inactivation was observed. This study demonstrated that HHP efficiently rendered the oocysts nonviable and noninfectious after treatment at 5.5 x 10(8) Pa.

Detection of Cryptosporidium oocysts in bivalve molluscs destined for human consumption

Clams (Dosinia exoleta, Ruditapes philippinarum, Venerupis pullastra, Venerupis rhomboideus, Venus verrucosa), mussels (Mytilus galloprovincialis), and oysters (Ostrea edulis) were tested for the presence of Cryptosporidium sp. oocysts using various stain techniques and a commercially available kit containing fluorescein isothiocyanate-conjugated monoclonal antibodies. All molluscs were harvested in northwest Spain (Galicia) except for R. philippinarum, which was from Italy, and 1 of the 6 oyster samples, which was from England. The results showed the presence of Cryptosporidium sp. oocysts in all of the molluscan species destined for human consumption.

Comparison of Cryptosporidium parvum viability and infectivity assays following ozone treatment of oocysts

Several in vitro surrogates have been developed as convenient, user-friendly alternatives to mouse infectivity assays for determining the viability of Cryptosporidium parvum oocysts. Such viability assays have been used increasingly to determine oocyst inactivation following treatment with chemical, physical, or environmental stresses. Defining the relationship between in vitro viability assays and oocyst infectivity in susceptible hosts is critical for determining the significance of existing oocyst inactivation data for these in vitro assays and their suitability in future studies. In this study, four viability assays were compared with mouse infectivity assays, using neonatal CD-1 mice. Studies were conducted in the United States and United Kingdom using fresh (<1 month) or environmentally aged (3 months at 4 degrees C) oocysts, which were partially inactivated by ozonation before viability and/or infectivity analyses. High levels of variability were noted within and between the viability and infectivity assays in the U.S. and United Kingdom studies despite rigorous control over oocyst conditions and disinfection experiments. Based on the viability analysis of oocyst subsamples from each ozonation experiment, SYTO-59 assays demonstrated minimal change in oocyst viability, whereas 4',6'-diamidino-2-phenylindole-propidium iodide assays, in vitro excystation, and SYTO-9 assays showed a marginal reduction in oocyst viability. In contrast, the neonatal mouse infectivity assay demonstrated significantly higher levels of oocyst inactivation in the U.S. and United Kingdom experiments. These comparisons illustrate that four in vitro viability assays cannot be used to reliably predict oocyst inactivation following treatment with low levels of ozone. Neonatal mouse infectivity assays should continue to be regarded as a "gold standard" until suitable alternative viability surrogates are identified for disinfection studies.

Study of the combined influence of environmental factors on viability of cryptosporidium parvum oocysts in water evaluated by fluorogenic vital dyes and excystation techniques

Using a factorial experimental design, the combined effect of salinity, temperature and storage time on the viability of Cryptosporidium parvum oocysts in water was evaluated by fluorogenic vital dyes (4',6-diamidino-2-phenylindole and propidium iodide) and an excystation technique. Salinity, storage time and their interaction seemed to be the most influential factors, whereas temperature was not a significant factor. Under unfavourable conditions (salinity 35 per thousand, storage time 40 days), even more than 20% of oocysts remain viable, indicating a high risk of infection for immunocompromised individuals.

Viability and infectivity of two Cryptosporidium parvum bovine isolates from different geographical location

The viability of two Cryptosporidium parvum bovine isolates from Spain and Colombia was evaluated by in vitro excystation, inclusion/exclusion of two fluorogenic vital dyes (DAPI and PI) and infectivity assay in a suckling murine model. Excystation percentages were similar for both Spain and Colombia isolates (83% and 87%, respectively). The total viability of the Spain isolate, measured by inclusion/exclusion of two fluorogenic vital dyes, was 71% in comparison with that detected for oocysts of the Colombia isolate, 32.3%. The bovine C. parvum oocysts of both isolates were viable and infectious for suckling Swiss CD-1 mice. However, infectivity percentage and the mean intensity of infection were consistently higher in the Spain isolate than those from Colombia isolate. It was not possible to obtain a good correlation between in vitro excystation, inclusion/exclusion of vital dyes and in vivo infectivity for the Colombia isolate, while data obtained with the Spain isolate indicated that there was an apparent strong correlation between excystation efficiency, total viability and the infectivity. Although a comparative analysis of genetic variation among these isolates from different geographical location is necessary, variations observed between the both isolates seemed to be a result of parasite adaptation to environmental stresses such as temperature which appears to have a direct effect on the permeability of the oocysts.

Detection of infectious Cryptosporidium parvum oocysts in mussels (Mytilus galloprovincialis) and cockles (Cerastoderma edule)

Infective Cryptosporidium parvum oocysts were detected in mussels (Mytilus galloprovincialis) and cockles (Cerastoderma edule) from a shellfish-producing region (Gallaecia, northwest Spain, bounded by the Atlantic Ocean) that accounts for the majority of European shellfish production. Shellfish were collected from bay sites with different degrees of organic pollution. Shellfish harboring C. parvum oocysts were recovered only from areas located near the mouths of rivers with a high density of grazing ruminants on their banks. An approximation of the parasite load of shellfish collected in positive sites indicated that each shellfish transported more than 10(3) oocysts. Recovered oocysts were infectious for neonatal mice, and PCR-restriction fragment length polymorphism analysis demonstrated a profile similar to that described for genotype C or 2 of the parasite. These results demonstrate that mussels and cockles could act as a reservoir of C. parvum infection for humans. Moreover, estuarine shellfish could be used as an indicator of river water contamination.

Comparative detection of Cryptosporidium parvum oocysts from apple juice

Drinking unpasteurized apple juice (or cider) has been associated with cryptosporidiosis, the diarrheal disease caused by the small protozoan parasite, Cryptosporidium parvum. This report compares detection of C. parvum oocysts from apple juice by acid-fast staining (AFS), direct immunofluorescence assay (DIFA), and polymerase chain reaction (PCR), following sample concentration by formalin-ethyl acetate sedimentation or sucrose flotation. Flotation was more efficient than sedimentation in recovering oocysts, and DIFA consistently detected lower numbers of oocysts than AFS. In combination, flotation-AFS could detect 3000 to 10,000 oocysts inoculated into 100 ml of apple juice while flotation-DIFA was able to detect as few as 100 oocysts. The highest sensitivity, 10 to 30 oocysts per 100 ml of apple juice, was achieved by DIFA following immunomagnetic capture (IC) of oocysts from samples concentrated by the flotation method. The detection limit of PCR following flotation or flotation IC was 30 to 100 oocysts; sequence analysis of the amplicon demonstrated that the PCR amplicon was C. parvum-specific.

Intact Cryptosporidium parvum oocysts isolated after in vitro excystation are infectious to neonatal mice

In vitro excystation is often used as a measure of viability of encysted protozoan parasites. Parasites that do not excyst in vitro are assumed to be non-viable and non-infectious, whereas those that do excyst are assumed viable. To test the validity of these assumptions, Cryptosporidium parvum oocysts were excysted in vitro using two different excystation protocols, and the non-excysted intact oocysts were isolated using flow cytometry. Non-excysted sorted oocysts readily infected neonatal CD-1 mice. Increasing the duration of the excystation assays from 1 h to 3 h resulted in a higher percent of excysted oocysts, but the remaining non-excysted parasites were still capable of infecting neonatal CD-1 mice. Our results suggest that in vitro excystation is not an accurate measure of the viability or infectious potential of C. parvum oocysts.

Cryptosporidiosis in birds--a review

The morphology, life cycle, maintenance, host specificity, incidence of Cryptosporidium species infecting birds, as well as the epidemiology, clinical signs, pathology, immunology, diagnosis, therapy, and control of avian cryptosporidiosis are reviewed. Based on the accepted criteria used for differentiation of Cryptosporidium isolates into valid species, this review places the validity of C. meleagridis in doubt and suggests that C. meleagridis isolated from birds is very closely related to, or identical with C. parvum infecting more than 100 species of mammals.

Use of green fluorescent protein to tag lactic acid bacterium strains under development as live vaccine vectors

The lactic acid bacteria (LAB) are safe microorganisms which are mainly used for the preparation of fermented foods and for probiotic applications. The potential of LAB as live vehicles for the production and delivery of therapeutic molecules such as antigens is also being actively investigated today. However, very little is known about the fate of live LAB when administered in vivo and about the interaction of these microorganisms with the nasal or gastrointestinal ecosystem. For future applications, it is essential to be able to discriminate the biotherapeutic strain from the endogenous microflora and to unravel the mechanisms underlying the postulated health-beneficial effect. We therefore started to investigate both aspects in a mouse model with two LAB species presently under development as live vaccine vectors, i.e., Lactococcus lactis and Lactobacillus plantarum. We have constructed different expression vectors carrying the gfp (green fluorescent protein [GFP]) gene from the jellyfish Aequoria victoria, and we found that this visible marker was best expressed when placed under the control of the inducible strong nisA promoter from L. lactis. Notably, a threshold amount of GFP was necessary to obtain a bright fluorescent phenotype. We further demonstrated that fluorescent L. plantarum NCIMB8826 can be enumerated and sorted by flow cytometry. Moreover, tagging of this strain with GFP allowed us to visualize its phagocytosis by macrophages in vitro and ex vivo and to trace it in the gastrointestinal tract of mice upon oral administration.

Comparison of animal infectivity and nucleic acid staining for assessment of Cryptosporidium parvum viability in water

Cryptosporidium parvum oocysts were stained with the fluorogenic dyes SYTO-9 and SYTO-59 and sorted by flow cytometry in order to determine whether the fluorescent staining intensity correlated with the ability of oocysts to infect neonatal CD-1 mice. Oocysts that did not fluoresce or that displayed weak fluorescent intensity when stained with SYTO-9 or SYTO-59 readily established infections in mice, whereas those oocysts that fluoresced brightly did not. Although fluorescent staining profiles varied among different batches of oocysts, a relative cutoff in fluorescent staining intensity that correlated with animal infectivity was observed for all batches.

Survival ofCryptosporidium parvumoocysts in source separated human urine

The survival of Cryptosporidium parvum in source separated urine was investigated as part of a broader study on microbial risks associated with the reuse of human urine for sustainable agriculture. A dye permeability assay and in vitro excystation were the primary methods used to assess viability. In the collected urine most of the nitrogen is present as ammonia and the pH is generally around 9. Parallel investigations were made in buffers to compare possible toxic effects of urine to actual pH effects. Oocysts in the untreated urine were inactivated below the detection limit (1/300) within 63 days. This inactivation rate was significantly higher (P < 0.01) than in urine adjusted to pH 5 or 7 according to the dye permeability assay. The corresponding difference between different pH values was not seen in buffers, suggesting that the antiprotozoan effect of urine was mediated by other factors besides pH. The Swedish practice of storing urine for six months before its use thus appears satisfactory for the inactivation of Cryptosporidium oocysts.Key words: Cryptosporidium parvum, oocysts, human urine, survival, source separation.

A most-probable-number assay for enumeration of infectious Cryptosporidium parvum oocysts

Cryptosporidium is globally established as a contaminant of drinking and recreational waters. A previously described cell culture infectivity assay capable of detecting infectious oocysts was adapted to quantify viable oocysts through sporozoite invasion and clustering of foci. Eight experiments were performed by using oocysts less than 4 months of age to inoculate host HCT-8 cell monolayers. Oocysts were diluted in a standard 5- or 10-fold multiple dilution format, levels of infection and clustering were determined, and the most probable number (MPN) of infectious oocysts in the stock suspension was calculated. The MPN was compared to the initial oocyst inoculum to determine the level of correlation. For oocysts less than 30 days of age, the correlation coefficient (r) was 0.9726 (0.9306 to 0.9893; n = 20). A two-tailed P value (alpha = 0.05) indicated that P was less than 0.0001. This strong correlation suggests that the MPN can be used to effectively enumerate infectious oocysts in a cell culture system. Age affected the degree of oocyst infectivity. Oocyst infectivity was tested by the focus detection method (FDM)-MPN assay and in BALB/c mice before and after treatment with pulsed white light (PureBrite). The FDM-MPN assay and animal infectivity assays both demonstrated more than a 4 log(10) inactivation. Municipal water systems and a host of other water testing organizations could utilize the FDM-MPN assay for routine survival and disinfection studies.

Long-term survival of Cryptosporidium parvum oocysts in seawater and in experimentally infected mussels (Mytilus galloprovincialis)

Transmission of infectious oocysts of Cryptosporidium parvum via surface- and drinking-water supplies has been reported and many surface waters flow into the sea, potentially causing runoff of animal-infected faeces. Eating raw mussels is a common practice in many countries, increasing the public's risk of acquiring enteric pathogens. The aims of the present study were to estimate how long C. parvum oocysts remain infectious in artificial seawater, to determine if the oocysts are retained in mussel tissues (Mytilus galloprovincialis), and how long they maintain their infectivity. Oocysts were incubated in artificial seawater at 6-8 degrees C under moderate oxygenation and the infectivity of oocysts was tested five times, over a 12 month period after incubation in seawater, in BALB/c mice. Each pup was inoculated per os with 10(5) oocysts and killed 5 days p.i. Oocysts remained infectious for 1 year. Forty mussels held in an aquarium containing artificial seawater filtered out more than 4 x 10(8) oocysts in a 24 h period. Oocysts were detected in the gill washing up to 3 days p.i., in the haemolymph up to 7 days p.i., and in the intestinal tract up to 14 days p.i. Oocysts collected from the gut of mussels 7 and 14 days p.i. were observed to have infected mice. These results suggest that C. parvum oocysts can survive in seawater for at least 1 year and can be filtered out by benthic mussels, retaining their infectivity up to 14 days, so seawater and molluscs are a potential source of C. parvum infection for humans.

Use of a sentinel system for field measurements of Cryptosporidium parvum oocyst inactivation in soil and animal waste

A small-volume sentinel chamber was developed to assess the effects of environmental stresses on survival of sucrose-Percoll-purified Cryptosporidium parvum oocysts in soil and animal wastes. Chambers were tested for their ability to equilibrate with external chemical and moisture conditions. Sentinel oocysts were then exposed to stresses of the external environment that affected their viability (potential infectivity), as indicated by results of a dye permeability assay. Preliminary laboratory experiments indicated that temperatures between 35 and 50 degrees C and decreases in soil water potential (-0.003 to -3.20 MPa) increased oocyst inactivation rates. The effects of two common animal waste management practices on oocyst survival were investigated on three dairy farms in Delaware County, N.Y., within the New York City watershed: (i) piling wastes from dairy youngstock (including neonatal calves) and (ii) spreading wastes as a soil amendment on an agricultural field. Sentinel containers filled with air-dried and sieved (2-mm mesh) youngstock waste or field soil were wetted and inoculated with 2 million oocysts in an aqueous suspension and then placed in waste piles on two different farms and in soil within a cropped field on one farm. Controls consisted of purified oocysts in either phosphate-buffered saline or distilled water contained in sealed microcentrifuge tubes. Two microdata loggers recorded the ambient temperature at each field site. Sentinel experiments were conducted during the fall and winter (1996 to 1997) and winter (1998). Sentinel containers and controls were removed at 2- to 4-week intervals, and oocysts were extracted and tested by the dye permeability assay. The proportions of potentially infective oocysts exposed to the soil and waste pile material decreased more rapidly than their counterpart controls exposed to buffer or water, indicating that factors other than temperature affected oocyst inactivation in the waste piles and soil. The effect of soil freeze-thaw cycles was evident in the large proportion of empty sentinel oocysts. The potentially infective sentinel oocysts were reduced to <1% while the proportions in controls did not decrease below 50% potentially infective during the first field experiment. Microscopic observations of empty oocyst fragments indicated that abrasive effects of soil particles were a factor in oocyst inactivation. A similar pattern was observed in a second field experiment at the same site.

Inactivation of Cryptosporidium parvum oocyst infectivity by disinfection and sterilization processes

BACKGROUND

Cryptosporidium parvum is a common cause of self-limited gastroenteritis in the normal host but may cause severe disease in immunocompromised persons. Person-to-person transmission has been well documented in households, child care centers, and hospitals. Because contaminated environmental surfaces and medical devices such as endoscopes may play a role in disease transmission, we studied the susceptibility of C parvum to chemical agents commonly used for disinfection and evaluated the efficacy of sterilization processes.

METHODS

Seven disinfectants were studied at their use dilution using a suspension test. Antimicrobial activity was assessed with the use of a cell infectivity assay.

RESULTS

All sterilization processes tested (steam, ethylene oxide, Sterrad 100) inactivated 3 logs or greater of C parvum. The only liquid disinfectant/sterilant able to inactivate greater than 3 logs of C parvum was 6% and 7.5% hydrogen peroxide. Agents that did not completely inactivate C parvum included hydrogen peroxide at lower concentrations or exposure times, peracetic acid, sodium hypochlorite, a phenolic, a quaternary ammonium compound, 2% glutaraldehyde, and ortho-phthalaldehyde.

CONCLUSIONS

Most high-level disinfectants used on endoscopes have limited efficacy against C parvum. However, the infectivity of C parvum on dry surfaces decreases rapidly. Therefore, current cleaning and high-level disinfection guidelines are adequate to prevent nosocomial transmission of C parvum by means of endoscopes.

Cryptosporidium parvum studies with dairy products

Cryptosporidium parvum is a protozoan parasite capable of causing massive waterborne outbreaks. This study was conducted to model the transfer of C. parvum oocysts from contaminated water via food contact surfaces into yogurt and ice-cream, as well as to examine oocyst survival. Propidium iodide staining, combined with a direct immunofluorescence assay, was used for oocyst viability determination. Oocysts were recovered from milk products by a sucrose flotation-based procedure, with average recoveries of 82.3, 60.7, and 62.5% from low (1%) fat milk, 9% fat ice-cream, and 98% fat-free yogurt, respectively. Oocysts were also recovered, by rinsing with tap water, from stainless steel surfaces inoculated with oocyst suspension, with average recoveries of 93.1% when the surface was still wet and 69.0% after the surface had air-dried at room temperature. Viability of oocysts on the surface was significantly affected by desiccation; 5% of the oocysts remained viable after 4 h of air-drying at room temperature, while the proportion of viable oocysts was 81, 69, and 45% after air-drying for 10 min, 1 h, and 2 h, respectively. In contrast, oocyst viability only dropped from 82 to 75% after 30 min contact at room temperature with 5% bleach solution (equivalent to 0.26% NaOCl). Transfer of oocysts from milk and stainless steel surfaces into yogurt, and oocyst survival during the process were analyzed. Yogurt was made from pasteurized low fat milk and live yogurt starter by incubating at 37 degrees C for 48 h and then stored at 4 degrees C. Oocyst viability decreased from 83% (80%) to approximately 60% after 48 h at 37 degrees C and to approximately 58% following 8 days of storage, similar to oocyst survival in the controls using pasteurized milk without the addition of live yogurt. Oocyst survival in ice-cream was investigated by inoculating oocysts into ice-cream mix, and mixing and freezing in an ice-cream freezer, and hardening at -20 degrees C. Although approximately 20% (25 and 18%) of oocysts were viable before hardening, none were viable after 24 h at -20 degrees C. Control samples of oocysts suspended in distilled water and stored at -20 degrees C were taken at the same time intervals and 8% of the oocysts were still viable after 24 h.

Sedimentation of free and attached Cryptosporidium oocysts and Giardia cysts in water

Experimental analysis of the sedimentation velocity of Cryptosporidium parvum oocysts and Giardia lamblia cysts was compared with mathematical description of their sedimentation velocities by using measurements of (oo)cyst size and density and the density and viscosity of the sedimentation medium to determine if the sedimentation kinetics of freely suspended oocysts of C. parvum and cysts of G. lamblia can be described by Stokes' law. The theoretically calculated sedimentation kinetics showed a good agreement with the experimentally observed kinetics. Both showed a decline in sedimentation velocity over time, caused primarily by variation in (oo)cyst density. The initial apparent sedimentation velocities in Hanks balanced salt solution at 23 degrees C was 0.35 micron . s-1 for oocysts and 1.4 micron . s-1 for cysts. (Oo)cysts that enter the surface water environment by discharges of biologically treated sewage may be attached to sewage particles, and this will affect their sedimentation kinetics. Therefore, (oo)cysts were mixed with settled secondary effluent. (Oo)cysts readily attached to the (biological) particles in effluent; 30% of both cysts and oocysts attached during the first minutes of mixing, and this fraction increased to approximately 75% after 24 h. The sedimentation velocity of (oo)cysts attached to secondary effluent particles increased with particle size and was (already in the smallest size fraction [1 to 40 micron]) determined by the sedimentation kinetics of the effluent particles. The observed sedimentation velocities of freely suspended (oo)cysts are probably too low to cause significant sedimentation in surface water or reservoirs. However, since a significant proportion of both cysts and oocysts attached readily to organic biological particles in secondary effluent, sedimentation of attached (oo)cysts after discharge into surface water will probably be a significant factor in the environmental ecology of C. parvum and G. lamblia. Attachment to particles influences not only sedimentation of (oo)cysts in surface water but also their behavior in drinking water treatment processes.

Influence of pretreatment and experimental conditions on electrophoretic mobility and hydrophobicity of Cryptosporidium parvum oocysts

Surface properties of Cryptosporidium parvum oocysts were investigated by using electrophoretic mobility and hydrophobicity measurements. Oocysts purified from calf feces by several sucrose flotation steps and deionized water (DI) washes (DIS method) had an electrophoretic mobility (neutral surface charge) near 0.0 m2 V-1 s-1 over a pH range of 2 to 10. The mean electrophoretic mobility of oocysts stored in DI containing a mixture of antibiotics had a lower standard deviation (sigma = 0.36) than that of oocysts stored in DI without antibiotics (sigma = 0.53); their electrophoretic mobility remained unchanged up to 121 days after collection. The electrophoretic mobility of oocysts purified on a cold Percoll-sucrose gradient after the feces was defatted with ethyl acetate (EAPS method) varied linearly with pH from 0.0 m2 V-1 s-1 at pH 2.4 to -3.2 x 10(-8) m2 V-1 s-1 at pH 10 (sigma = 0.52), thus displaying the negative surface charge at neutral pH observed by other researchers. The hydrophobicity of oocysts and two types of polystyrene beads was measured as a function of ionic strength by adhesion to polystyrene. Oocysts were purified by the DIS method. The ionic strength of the suspending solution was varied from 0 to 95 mmol liter-1. Two-week-old oocysts exhibited strong adhesion ( approximately 85%) at ionic strengths of 0 to 10 mmol liter-1 and moderate adhesion ( approximately 20%) at ionic strengths of 20 to 95 mmol liter-1. Two-month-old oocysts exhibited high adhesion ( approximately 60 to 80%) at all ionic strengths. These results show that adhesion properties governed by the electrophoretic mobility of purified C. parvum oocysts can be altered by the method of purification and that hydrophobicity can change as oocysts age.

Oocysts of Cryptosporidium from snakes are not infectious to ducklings but retain viability after intestinal passage through a refractory host

Six 2-week-old Cryptosporidium-free Peking ducklings (Anas platyrhynchos) each received 2.0 x 10(6) viable Cryptosporidium serpentis oocysts from 6 naturally infected captive snakes. Histological sections of digestive (stomach, jejunum, ileum, cloaca, and cecum) and respiratory tract tissues (larynx, trachea, and lungs) did not contain life-cycle stages of Cryptosporidium in any of the inoculated ducklings. Because ducklings were refractory to infection, C. serpentis transmission via a diet of Peking ducklings is improbable. Viable (per in vitro excystation assay) inoculum-derived oocysts were detected in duckling feces up to 7 days post-inoculation (PI); the number of intact oocysts excreted during the first 2 days PI was significantly higher than for the remaining 5 days PI (P < 0.01). The dynamics of oocyst shedding showed that overall the birds released a significantly higher number of intact oocysts than oocyst shells (P < 0.01). Retention of the viability of C. serpentis oocysts following intestinal passage through a refractory avian species may have epizootiological implications. Under certain circumstances such as after the ingestion of C. serpentis-infected prey, herpetivorous birds may disseminate C. serpentis oocysts in the environment.

Hydrogen peroxide gas plasma sterilization is effective against Cryptosporidium parvum oocysts

The aim of this work was to evaluate in an immunosuppressed rat cryptosporidiosis model a new method that combines vacuum and low-temperature hydrogen peroxide gas plasma for sterilization of endoscopic material contaminated by Cryptosporidium parvum. Rats were challenged with oocysts either air-dried or air-dried and treated with vacuum alone or associated with gas plasma. No rat was found infected after gas plasma exposure of oocysts, whereas vacuum or air-drying alone resulted only in a decreased infectivity.

Survival of infectious Cryptosporidium parvum oocysts in seawater and eastern oysters (Crassostrea virginica) in the Chesapeake Bay

Oocysts of Cryptosporidium parvum placed in artificial seawater at salinities of 10, 20, and 30 ppt at 10 degrees C and at 10 ppt at 20 degrees C were infectious after 12 weeks. Those placed in seawater at 20 ppt and 30 ppt at 20 degrees C were infectious for 8 and 4 weeks, respectively. These findings suggested that oocysts could survive in estuarine waters long enough to be removed by filter feeders such as oysters. Thereafter, 30 Eastern oysters, Crassostrea virginica, were collected with a dredge or with hand tongs at each of six sites within Maryland tributaries of the Chesapeake Bay in May and June and in August and September of 1997. Hemocytes and gill washings from all oysters were examined for the presence of Cryptosporidium oocysts and Giardia cysts by immunofluorescence microscopy utilizing a commercially available kit containing fluorescein isothiocyanate-conjugated monoclonal antibodies. Giardia was not detected by this method from any of the 360 oysters examined. Presumptive identification of Cryptosporidium oocysts was made in either hemocytes or gill washings of oysters from all six sites both times that surveys were conducted. In addition, during August and September, for each of the six sites, hemocytes from the 30 oysters were pooled and gill washings from the oysters were pooled. Each pool was delivered by gastric intubation to a litter of neonatal mice to produce a bioassay for oocyst infectivity. Intestinal tissue from two of three mice that received gill washings from oysters collected at a site near a large cattle farm and shoreline homes with septic tanks was positive for developmental stages of C. parvum. These findings demonstrate for the first time that oysters in natural waters harbor infectious C. parvum oocysts and can serve as mechanical vectors of this pathogen.

Inactivation of Cryptosporidium parvum Oocysts by Ammonia

The survival of Cryptosporidium parvum oocysts in soil and water microhabitats may be affected by the environmental production and release of free ammonia. The objective of this study was to determine the effects of increasing free ammonia concentrations and times of exposure on oocyst viability. Wild-type oocysts were obtained from naturally infected calf feces by chemical (continuous-flow) centrifugation and sucrose gradients. Ammonia (NH 3 ) from a commercial solution was applied in concentrations ranging from 0.007 to 0.148 M. Exposure times ranged from 10 min to 24 h at a constant temperature of 24 ± 1°C. Viability of oocysts was determined with a dye permeability assay and an in vitro excystation assay (M. B. Jenkins, L. J. Anguish, D. D. Bowman, M. J. Walker, and W. C. Ghiorse, Appl. Environ. Microbiol. 63:3844–3850, 1997). Even the lowest concentration of ammonia decreased significantly the viability of oocysts after 24 h of exposure. Increasing concentrations of ammonia increased inactivation rates, which ranged from 0.014 to 0.066 h −1 . At the highest concentration of ammonia, a small fraction of viable oocysts still remained. Exposure to pH levels corresponding to those associated with the ammonia concentrations showed minimal effects of alkaline pH alone on oocyst viability. This study shows that environmentally relevant concentrations of free ammonia may significantly increase the inactivation of oocysts in ammonia-containing environments.

Nosocomial transmission of Cryptosporidium in a veterinary hospital

An outbreak of cryptosporidiosis occurred at a veterinary hospital, involving multiple species, including humans. The index case was an infected dairy calf that presented with diarrhea. Several other cases of cryptosporidial diarrhea subsequently developed during a 1-month period. The key features of this outbreak were the multiple species affected, the increased morbidity in immunocompromised neonates, and the failure of implemented control measures to contain the disease.

Simple and rapid measurement of Cryptosporidium excystation using flow cytometry

In vitro excystation is commonly used to determine the viability of samples of purified Cryptosporidium parvum oocysts. Following exposure to conditions that stimulate excystation, samples are examined microscopically to determine the number of excysted oocysts. The microscopy procedure is tedious and time consuming, and difficult to apply to most oocyst samples without a purification step. A simple flow cytometric method was developed for determining the numbers of oocysts that had excysted following the in vitro excystation procedure. Differences in light-scatter properties were used to differentiate intact, partially empty and empty oocysts. By staining samples with a monoclonal antibody specific to the oocyst wall it was possible to apply the technique to unpurified oocysts from faeces. Correlation of the flow cytometric and microscopic method was statistically significant (P < 0.05), resulting in a calculated correlation coefficient of 0.994. The flow cytometry method is faster and more sensitive than the microscopy procedure, and enables analysis of large numbers of samples and of many thousands of oocysts in each sample.

Assessment of a dye permeability assay for determination of inactivation rates of Cryptosporidium parvum oocysts

The ability to determine inactivation rates of Cryptosporidium parvum oocysts in environmental samples is critical for assessing the public health hazard of this gastrointestinal parasite in watersheds. We compared a dye permeability assay, which tests the differential uptake of the fluorochromes 4'-6-diamidino-2-phenylindole (DAPI) and propidium iodide (PI) by the oocysts (A. T. Campbell, L. J. Robertson, and H. V. Smith, Appl. Environ. Microbiol. 58:3488-3493, 1992), with an in vitro excystation assay, which tests their ability to excyst and, thus, their metabolic potential and potential for infectivity (J.B. Rose, H. Darbin, and C.P. Gerba, Water Sci. Technol. 20:271-276, 1988). Formaldehyde-fixed (killed) oocysts and untreated oocysts were permeabilized with sodium hypochlorite and subjected to both assays. The results of the dye permeability assays were the same, while the excystation assay showed that no excystation occurred in formaldehyde-fixed oocysts. This confirmed that oocyst wall permeability, rather than metabolic activity potential, was the basis of the dye permeability viability assessment. A previously developed protocol (L. J. Anguish and W. C. Ghiorse, Appl. Environ. Microbiol. 63:724-733, 1997) for determining viability of oocysts in soil and sediment was used to examine further the use of oocyst permeability status as an indicator of oocyst viability in fecal material stored at 4 degrees C and in water at various temperatures. Most of the oocysts in fresh calf feces were found to be impermeable to the fluorochromes. They were also capable of excystation, as indicated by the in vitro excystation assay, and were infective, as indicated by a standard mouse infectivity assay. The dye permeability assay further showed that an increase in the intermediate population of oocysts permeable to DAPI but not to PI occurred over time. There was also a steady population of oocysts permeable to both dyes. Further experiments with purified oocysts suspended in distilled water showed that the shift in oocyst populations from impermeable to partially permeable to fully permeable was accelerated at temperatures above 4 degrees C. This sequence of oocyst permeability changes was taken as an indicator of the oocyst inactivation pathway. Using the dye permeability results, inactivation rates of oocysts in two fecal pools stored in the dark at 4 degrees C for 410 and 259 days were estimated to be 0.0040 and 0.0056 oocyst day-1, respectively. The excystation assay gave similar inactivation rates of 0.0046 and 0.0079 oocyst day-1. These results demonstrate the utility of the dye permeability assay as an indicator of potential viability and infectivity of oocysts, especially when combined with improved microscopic methods for detection of oocysts in soil, turbid water, and sediments.

An in vitro method for detecting infectious Cryptosporidium oocysts with cell culture

Current assay methods to detect Cryptosporidium oocysts in water are generally not able to evaluate viability or infectivity. A method was developed for low-level detection of infective oocysts by using HCT-8 cells in culture as hosts to C. parvum reproductive stages. The infective foci were detected by labeling intracellular developmental stages of the parasite in an indirect-antibody assay with a primary antibody specific for reproductive stages and a secondary fluorescein isothiocyanate-conjugated antibody. The complete assay was named the focus detection method (FDM). The infectious foci (indicating that at least one of the four sporozoites released from a viable oocyst had infected a cell) were enumerated by epifluorescence microscopy and confirmed under Nomarski differential interference contrast microscopy. Time series experiments demonstrated that the autoreinfective life cycle in host HCT-8 cells began after 12 h of incubation. Through dilution studies, levels as low as one infectious oocyst were detected. The cell culture FDM compared well to other viability assays. Vital stains and excystation demonstrated that oocyst populations less than 1% viable (by vital dyes) and having a low sporozoite yield following excystation could not infect host cells. Until now, the water industry has relied on an oocyst detection method (under an information collection regulation) that is unable to determine viability. The quantifiable results of the cell culture method described demonstrate two important applications: (i) an infectivity assay that may be used in conjunction with current U.S. Environmental Protection Agency-mandated detection methodologies, and (ii) a method to evaluate oocyst infectivity in survival and disinfection studies.

Immunomagnetic capture PCR to detect viable Cryptosporidium parvum oocysts from environmental samples

A method to detect viable Cryptosporidium parvum oocysts was developed. Polyclonal immunoglobulin G against C. parvum oocyst and sporozoite surface antigens was purified from rabbit immune serum, biotinylated, and bound to streptoavidin-coated magnetic particles. C. parvum oocysts were captured by a specific antigen-antibody reaction and magnetic separation. The oocysts were then induced to excyst, and DNA was extracted by heating at 95 degrees C for 10 min. A 452-bp fragment of C. parvum DNA was amplified by using a pair of C. parvum-specific primers in PCR. The method detected as few as 10 oocysts in purified preparations and from 30 to 100 oocysts inoculated in fecal samples. The immunomagnetic capture PCR (IC-PCR) product was identified and characterized by a nested PCR that amplified a 210-bp fragment, followed by restriction endonuclease digestion of the IC-PCR and nested-PCR products at the StyI site and a nonradioactive hybridization using an internal oligonucleotide probe labeled with biotin. PCR specificity was also tested, by using DNAs from other organisms as templates. In the control experiments, inactivated oocysts were undetectable, indicating the ability of this method to differentiate between viable and nonviable oocysts. Thus, this system can be used to specifically detect viable C. parvum oocysts in environmental samples with great sensitivity, providing an efficient way to monitor the environment for C. parvum contamination.

Nucleic acid stains as indicators of Cryptosporidium parvum oocyst viability

We developed nucleic acid dye staining methodology for untreated, heat-treated and chemically inactivated C. parvum oocysts. The nucleic acid staining was compared to in vitro excystation and animal infectivity using split samples of oocysts. Among the nucleic acid stains tested, SYTO-9, hexidium and SYTO-59 stained the oocysts consistently, and the staining was related to the infectivity of the oocysts to neonatal CD-1 mice but not to in vitro excystation. The nucleic acid viability assay was used to determine log-inactivations of the oocysts after treatment with ozone, chlorine, chlorine dioxide and combinations of different chemical disinfectants, and was found to indicate log-inactivation levels similar to that of animal infectivity. A combined immunofluorescence-nucleic acid staining assay was developed for the oocysts of C. parvum and this assay will be invaluable for the detection and viability of oocysts in the laboratory and in environmental samples.

Cryptosporidium sp. Infections in Green Turtles, Chelonia mydas, as a Potential Source of Marine Waterborne Oocysts in the Hawaiian Islands

For the first time, Cryptosporidium sp. oocysts were identified in fecal and intestinal samples from free-ranging marine turtles, Chelonia mydas, from the Hawaiian Islands. The oocysts produced positive reactions with commercial test kits recommended for the detection of human-infectious waterborne oocysts of Cryptosporidium parvum.

Effect of a commercial disinfectant ('Virkon') on mouse experimental infection by Cryptosporidium parvum

Cryptosporidium parvum oocysts obtained from naturally-infected calves were exposed to 1-10% 'Virkon' for 10-360 min, then inoculated intragastrically into coccidium-free neonatal mice. Prevalence and intensity of infection were determined seven days later by examination of intestinal homogenates. Although we were unable to abolish infectivity for the mice, the intensity of infection was considerably reduced after long periods of exposure (up to > 90%, depending on disinfectant concentration), indicating that this product may have some value for disinfection when extended exposure is possible (e.g., soaking laboratory glassware).