Removal Of Oocysts Research Articles

Upflow Direct Filtration and Downflow Direct Filtration: A Comparison with Emphasis on the Removal of Aerobic Spore-Forming Bacteria and Fluorescent Microspheres as Surrogates for Cryptosporidium Oocyst Removal

Monitoring the removal of Cryptosporidium oocysts in water treatment plants is a challenge, particularly in developing countries, and the use of surrogates has proven necessary. Two surrogates already investigated and recognized by the scientific community are aerobic spore-forming bacteria (ASFB) and fluorescent polystyrene microspheres (ME). In this context, this study evaluates and compares the performance of upflow direct filtration and downflow direct filtration, with emphasis on the removal of ASFB and ME as a surrogate of Cryptosporidium oocyst removal. Pilot filtration experiments were carried out with low turbidity Paranoá Lake water (average—3.7 NTU) with ASFB varying from 7 × 102 to 5.5 × 103 CFU/100 mL. In some experiments, water was spiked with microspheres, aiming for 105 ME/L. Two operational conditions were evaluated: (1) filters operating with the same filtration rate (5 m/h); (2) filters operating with the same flow rate of 59.41 L/h. In general, the downflow filter presented a slightly higher removal efficiency than the upflow filter but the differences were not considered statistically significant in most cases. The removal efficiency of microspheres (3 to 5 log) was higher than that of ASFB (1.2 to 4 log) in both filters, corroborating that the removal of ASFB is a conservative surrogate of the removal of Cryptosporidium.

Fate of Cryptosporidium and Giardia through conventional and compact drinking water treatment plants

Over the past three decades, a notable rise in the occurrence of enteric protozoan pathogens, especially Giardia and Cryptosporidium spp., in drinking water sources has been observed. This rise could be attributed not only to an actual increase in water contamination but also to improvements in detection methods. These waterborne pathogens have played a pivotal role in disease outbreaks and the overall escalation of disease rates in both developed and developing nations worldwide. Consequently, the control of waterborne diseases has become a vital component of public health policies and a primary objective of drinking water treatment plants (DWTPs). Limited studies applied real-time PCR (qPCR) and/or immunofluorescence assay (IFA) for monitoring Giardia and Cryptosporidium spp., particularly in developing countries like Egypt. Water samples from two conventional drinking water treatment plants and two compact units (CUs) were analyzed using both IFA and qPCR methods to detect Giardia and Cryptosporidium. Using qPCR and IFA, the conventional DWTPs showed complete removal of Giardia and Cryptosporidium, whereas Mansheyat Alqanater and Niklah CUs achieved only partial removal. Specifically, Cryptosporidium gene copies removal rates were 33.33% and 60% for Mansheyat Alqanater and Niklah CUs, respectively. Niklah CU also removed 50% of Giardia gene copies, but no Giardia gene copies were removed by Mansheyat Alqanater CU. Using IFA, both Mansheyat Alqanater and Niklah CUs showed a similar removal rate of 50% for Giardia cysts. Additionally, Niklah CU achieved a 50% removal of Cryptosporidium oocysts, whereas Mansheyat Alqanater CU did not show any removal of Cryptosporidium oocysts. Conventional DWTPs were more effective than CUs in removing enteric protozoa. The contamination of drinking water by enteric pathogenic protozoa remains a significant issue globally, leading to increased disease rates. Infectious disease surveillance in drinking water is an important epidemiological tool to monitor the health of a population.

Improved operational reliability and contaminant removal in water reuse through filter upgrades

AbstractA redesign, construction, and replacement of the filters used for water reuse at a 11 million gallon per day Florida municipal water reclamation facility provided a prime opportunity to evaluate the impact of the filtration technologies on water quality, trace organic contaminant (TOrC) removal, and removal of pathogens. This study was designed to capture operational data, pathogen removal (Cryptosporidium and Giardia), and TOrC removal before the replacement of the filters using the existing synthetic media filters (SMF) and traveling bridge filters (TBF) followed by an evaluation of the deep bed filters (DBF) after construction and commissioning. The new DBF units provided substantially improved control of turbidity and total suspended solids while also significantly improving the removal of Giardia cysts (increase of >2 log removal) as compared to removal across the older SMF and TBF units and minor improvements to Cryptosporidium oocyst removal. TOrC removal was not significantly changed when comparing removal across the SMF, TBF, and DBF units nor post chlorination (chloramination).Article Impact StatementThis manuscript will be of use to the community as it provides additional understanding of public health protection in water reuse.

Filter media depth and its effect on the efficiency of Household Slow Sand Filter in continuous flow

This study evaluated the impact of a 50% reduction of filter media depth in Household Slow Sand Filters (HSSFs) on continuous flow to remove physicochemical and microbiological parameters from river water. Furthermore, simple pre-treatment and disinfection processes were evaluated as additional treatments. Two filter models with different filtration layer depths were evaluated: a traditional one with 50 cm media depth (T-HSSF) and a compact one (C-HSSF) with 25 cm. HSSFs were fed with pre-treated river water (24-h water sedimentation followed by synthetic fabric filtration) for 436 days at a constant filtration rate of 0.90 m3 m−2 day−1 with a daily production of 48 L day−1. Sodium hypochlorite (2.0 mg L−1 of NaOCl 2.5% for 30 min) was used to disinfect the filtered water. Water samples were analysed weekly for parameters such as turbidity, organic matter, colour and E. coli, among others. Removal of protozoan cysts and oocysts by the HSSFs were also evaluated. After pretreatment, turbidity from the HSSF river water was reduced to 13.2 ± 14.6 NTU, allowing the filters to operate. Statistical analysis indicated no significant difference (p > 0.05) between T-HSSF and C-HSSF efficiencies in all evaluated parameters throughout operation time. Hence, media depth reduction did not hinder continuous HSSF performance for almost all the evaluated parameters. However, it may have affected Giardia cysts retaining, which passed through the thinner media on one evaluation day. Disinfection was effective in reducing remaining bacteria from filtered water; however, it was ineffective to inactivate protozoa. The reduction in the filtration layer did not affect the overall filtered water quality or quantity showing that a compact HSSF model may be a viable option for decentralized water treatment.

Detection and removal of Giardia spp. cysts and Cryptosporidium spp. oocysts by anaerobic reactors in Brazil

ABSTRACT The discharge of raw wastewater into the environment can be a contamination source of Giardia spp. cysts and Cryptosporidium spp. oocysts. The UASB (Upflow Anaerobic Sludge Blanket) reactor is the most popular technology applied for wastewater treatment in Brazil, nevertheless there is little information concerning its capacity for (oo)cyst removal. In this context, this study investigated the occurrence and removal of Giardia spp. cysts and Cryptosporidium spp. oocysts by three different UASB reactors (i.e. Reactor A, B, and C) treating different wastewater types. In the wastewater influent, the concentration varied from 493.3 to 14,000 cysts·L-1 for Giardia spp. and from ‘not detected’ to 53.3 oocysts·L-1 for Cryptosporidium spp.. The (oo)cyst concentration increased after the anaerobic treatment in Reactors A and B, while Giardia spp. log-removal of 0.5 ± 0.2 was found in Reactor C. The increment in (oo)cyst concentration may happened due to the inefficacy for (oo)cyst removal by the specific UASB reactor and/or due to the reduction of matrix interference for reactor effluent samples in the detection method. The results suggest that hydraulic retention time (HRT) may be the key parameter for Giardia spp. removal by the UASB reactor. Furthermore, no parameter analysed (physical-chemical and indicator microorganisms) showed a common correlation with the (oo)cyst concentration in the three UASB reactors. Considering that official data of cryptosporidiosis and giardiasis cases are rarely reported in Brazil, monitoring Giardia spp. cysts and Cryptosporidium spp. oocysts in wastewater could be an alternative to estimate the occurrence of diseases in the served population.

Cryptosporidium Oocysts Removal by Upflow Direct Filtration: Pilot Scale Assessment

Studies on the removal of Cryptosporidium oocysts by direct filtration suggested that high removal efficiencies (>3.0 log) can be achieved, but the vast majority of the studies focused on the assessment of downflow direct filtration. However, in comparison with downflow direct filtration, filters in upflow direct filtration systems use lower filtration rates, deeper stratified bed, and water flows from coarse to fine sand grain, which may improve the removal of oocysts. In this context, we evaluated the removal of Cryptosporidium oocysts using upflow direct filtration, on a pilot scale, to treat Paranoá Lake water (Brazil) seeded with Cryptosporidium oocysts. The experiments were conducted with raw water with low turbidity (3.2–5.7 NTU) and induced higher turbidity (28–30 NTU). Non-parametric statistical analysis was used to verify correlations between the filtered water values and removal of oocysts, particles, and turbidity. In general, no correlation was observed between the parameters analyzed, nor between their removals. The exception was the correlation between residual values of Cryptosporidium oocysts and particles of 2 to 7 µm during ripening, an aspect that needs further evaluation. Under stable operation, average removal of Cryptosporidium oocysts by upflow direct filtration was >3.87 log. During ripening, removal of oocysts was around 1 log lower.

Role of filtration in managing the risk from Cryptosporidium in commercial swimming pools - a review.

Most commercial swimming pools use pressurised filters, typically containing sand media, to remove suspended solids as part of the water treatment process designed to keep water attractive, clean and safe. The accidental release of faecal material by bathers presents a poorly quantified risk to the safety of swimmers using the pool. The water treatment process usually includes a combination of maintaining a residual concentration of an appropriate biocide in the pool together with filtration to physically remove particles, including microbial pathogens, from the water. However, there is uncertainty about the effectiveness of treatment processes in removing all pathogens, and there has been growing concern about the number of reported outbreaks of the gastrointestinal disease cryptosporidiosis, caused by the chlorine-resistant protozoan parasite Cryptosporidium. A number of interacting issues influence the effectiveness of filtration for the removal of Cryptosporidium oocysts from swimming pools. This review explains the mechanisms by which filters remove particles of different sizes (including oocyst-sized particles, typically 4-6 μm), factors that affect the efficiency of particle removal (such as filtration velocity), current recommended management practices, and identifies further work to support the development of a risk-based management approach for the management of waterborne disease outbreaks from swimming pools.

Removal of model viruses, E. coli and Cryptosporidium oocysts from surface water by zirconium and chitosan coagulants.

The present work evaluates the effect of contact filtration, preceded by coagulation with zirconium (Zr) and chitosan coagulants, on model microorganisms and waterborne pathogens. River water intended for potable water production was spiked with MS2 and Salmonella Typhimurium 28B bacteriophages, Escherichia coli, and Cryptosporidium parvum oocysts prior to coagulation. The hygienic performance demonstrated by Zr comprised 3.0-4.0 log10 removal of viruses and 5.0-6.0 log10 removal of E. coli and C. parvum oocysts. Treatment with chitosan resulted in a removal of 2.5-3.0 log10 of viruses and parasites, and 4.5-5.0 log10 of bacteria. A reference coagulant, polyaluminium chloride (PACl), gave a 2.5-3.0 log10 removal of viruses and 4.5 log10 of E. coli. These results indicate that both Zr and chitosan enable adequate removal of microorganisms from surface water. The present study also attempts to assess removal rates of the selected microorganisms with regard to their size and surface properties. The isoelectric point of the Salmonella Typhimurium 28B bacteriophage is reported for the first time. The retention of the selected microorganisms in the filter bed appeared to have some correlation with their size, but the effect of the charge remained unclear.

Removals of cryptosporidium parvum oocysts and cryptosporidium-sized polystyrene microspheres from swimming pool water by diatomaceous earth filtration and perlite-sand filtration.

Removal of Cryptosporidium-sized microspheres and Cryptosporidium parvum oocysts from swimming pools was investigated using diatomaceous earth (DE) precoat filtration and perlite-sand filtration. In pilot-scale experiments, microsphere removals of up to 2 log were obtained with 0.7 kg·DE/m2 at a filtration rate of 5 m/h. A slightly higher microsphere removal (2.3 log) was obtained for these DE-precoated filters when the filtration rate was 3.6 m/h. Additionally, pilot-scale perlite-sand filters achieved greater than 2 log removal when at least 0.37 kg/m2 of perlite was used compared to 0.1-0.4 log removal without perlite both at a surface loading rate of 37 m/h. Full-scale testing achieved 2.7 log of microspheres and oocysts removal when 0.7 kg·DE/m2 was used at 3.6 m/h. Removals were significantly decreased by a 15-minute interruption of the flow (without any mechanical agitation) to the DE filter in pilot-scale studies, which was not observed in full-scale filters. Microsphere removals were 2.7 log by perlite-sand filtration in a full-scale swimming pool filter operated at 34 m/h with 0.5 kg/m2 of perlite. The results demonstrate that either a DE precoat filter or a perlite-sand filter can improve the efficiency of removal of microspheres and oocysts from swimming pools over a standard sand filter under the conditions studied.

Cryptosporidium Attenuation across the Wastewater Treatment Train: Recycled Water Fit for Purpose.

Compliance with guideline removal targets for Cryptosporidium which do not provide any credit for the inactivation of oocysts through wastewater treatment processes can considerably increase the cost of providing recycled water. Here we present the application of an integrated assay to quantify both oocyst numbers and infectivity levels after various treatment stages at three Victorian and two South Australian (SA) wastewater treatment plants (WWTPs). Oocyst density in the raw sewage was commensurate with community disease burden, with early rounds of sampling capturing a widespread cryptosporidiosis outbreak in Victoria. The level of infectivity of oocysts in sewage was stable throughout the year but was significantly lower at the SA WWTPs. Removals across secondary treatment processes were seasonal, with poorer removals associated with inflow variability; however, no decrease in the oocyst infectivity was identified. For SA WWTPs, those oocysts remaining within the secondary treatment-clarified effluent were proportionally more infectious than those in raw sewage. Lagoon systems demonstrated significant inactivation or removal of oocysts, with attenuation being seasonal. Examination of a UV system emphasized its efficacy as a disinfectant barrier but conversely confirmed the importance of a multibarrier approach with the detection of infectious oocysts postdisinfection. The ability to characterize risk from infectious oocysts revealed that the risk from Cryptosporidium is significantly lower than previously thought and that its inclusion in quantitative risk assessments of reuse systems will more accurately direct the selection of treatment strategies and capital expenditure, influencing the sustainability of such schemes.IMPORTANCE Here we present the application of a recently developed integrated assay not only to quantify the removal of Cryptosporidium oocysts but also to quantify their infectivity across various treatment stages at five wastewater treatment plants (WWTPs), thereby better measuring the "true effect" of the treatment train on oocyst risk reduction. For a number of the WWTPs analyzed in this study the risk, is significantly lower than previously thought. Therefore, the inclusion of oocyst infectivity in guideline values and in quantitative microbial risk assessment (QMRA) has the potential to affect future treatment directions and capital expenditure.

Recent Development of Chitosan Nanocomposites for Environmental Applications.

Potable, clean and safe water is the basic need for all human beings. Major portion of the earth is occupied by water, however, this is contaminated by rapid industrialization, improper sewage and natural calamities and man-made activates, which produce several water-borne and fetal diseases. In this review we presented some recent patent for environmental remediation. Various technologies have been developed for the treatment of waste water consist of chemical, membrane, filtration, sedimentation, chlorination, disinfection, electrodialysis, electrolysis, reverse osmosis and adsorption. Among these entire phenomenon's, adsorption was the most efficient method for wastewater treatment, because it is a quick and cheap technology which signifies extensive practical applications. Adsorption phenomenon has been tactfully used for the removal of biological waste as well as soluble and insoluble material with a removal efficacy of 90-99%. Clean water supply is limited to human beings. The people in the developing countries have less or no access to the clean and potable water. The shortage of potable water resources and long term safe water deficiencies are some of the leading problems worldwide. In this review, we have explained in the detail adsorption phenomena of chitosan, pharmaceutical importance and other applications. It is worth to say that adsorption technologies using chitosan and its derivative is one of the quickest and cost effective methods for the wastewater treatment. The review comprises of ninety eight references. This review also covers various patents vis-a-vis the role of chitosan-nanocomposite in environmental application for wastewater treatment. Chitosan is a pseudo-neutral cationic polymer which is formed by the de-acetylation of chitin polymer. Various patent on chitosan and chitosan-nanocomposite were taken into account related to wastewater purification. We have found that chitosan and chitosan-nanocomposite are used for the removal of viruses, bacteria, cryptosporidium oocysts and giardia cysts, soluble and insoluble organic pollutants, poly aromatic hydrocarbons and heavy metals from wastewater. In this study, we also found that chitosan and chitosan-nanocomposite are selected for the removal of transition metals.

A full-scale study of Cryptosporidium parvum oocyst and Cryptosporidium-sized microsphere removals from swimming pools via sand filtration

Removal of Cryptosporidium parvum oocysts and Cryptosporidium-sized microspheres was evaluated in full-scale swimming pools via high-rate sand filtration (31–34 m/h) with coagulation. Results showed that at least 90% of C. parvum oocysts and microspheres were removed by filtration with an initial dosage of coagulant B (1.56 mg/L), D (1.9 mg/L or 305 g/m2), or F (1.56 mg/L) from each swimming pool. Filtration with an initial dosage of coagulant E (0.1 mg·Al/L) achieved 82% C. parvum oocyst removal and 97% microsphere removal. Coagulants B and F had a tendency to overdose over time with continuous feeding (based on corresponding pilot-scale experiments) and did not consistently achieve removals greater than 90% in the full-scale trials. As high as 99% of C. parvum oocysts and 98% of microspheres were removed with a continuous dosage of coagulant D. Up to 98% (1.7 log) of C. parvum oocysts and 93% (1.1 log) of microspheres were removed by continuous dosing of coagulant E at 27 m/h. Consistent oocyst and microsphere removal by aluminum-based coagulants (D and E) was achieved under the tested swimming pool conditions.

Cryptosporidium risk from swimming pool exposures.

Infection risk estimates from swimming in treated recreational water venues are lacking and needed to prioritize public health interventions in swimming pools. Quantitative infection risk estimates among different age groups are needed to identify vulnerable populations. High risk populations can be targeted during public health interventions, like education campaigns and pool operation improvements. This study estimated per-swim and annual Cryptosporidium infection risks in adults (>18) and children (≤18) using new experimental data collected in the U.S. on swimmer behavior. Risks were estimated using oocyst concentration data from the literature, and data collected in this study on pool water ingestion, swim duration and pool use frequency. A sensitivity analysis identified the most influential model variables on infection probability. The average estimated risk of Cryptosporidium infection was 2.6×10-4 infections/swim event. The per-swim risk estimate in the present study differed from others because behavior data (ingestion rates, swim duration, and visit frequency) were collected in different countries and varied from U.S. estimates. We found swimmer behaviors influence infection risk. This is the first study to report annual risk of Cryptosporidium infection among swimmers by age group. Using U.S. exposure data, annual risk was estimated at 2.9×10-2 infections/year for children and 2.2×10-2 infections/year for adults. Annual risk for all swimmers was estimated at 2.5×10-2 infections/year from swimming in treated recreational water venues. Due to increased ingestion and swim duration, child swimmers had the highest annual risk estimate. Cryptosporidium concentration is the most influential variable on infection probability. Results suggest the need for standardized pool water quality monitoring for Cryptosporidium, education, development of interventions to reduce ingestion, consideration of behaviors unique to swimming populations in future risk assessments and improvement of oocyst removal from pool water. Child swimmers were the most vulnerable sub-population, and should be targeted in healthy swimming education campaigns.

Removal of Cryptosporidium parvum oocysts in low quality water using Moringa oleifera seed extract as coagulant

The use of different types of low quality water for irrigation in agriculture is common practice in many countries due to limited freshwater resources. Pathogens may contaminate fruit and vegetables when feces contaminated water is used for irrigation or postharvest processing. A laboratory study was carried out to investigate the effect of a coagulant produced from seeds of the Moringa oleifera tree (MO) in reducing Cryptosporidium parvum oocysts and turbidity in wastewater and stream water. Glass jars (n=60) containing 500mL wastewater obtained from the inlet to the primary settling tanks from a Danish sewage treatment plant were spiked with 6.1x105±6.2×104oocystsL−1, while glass jars (n=18) containing 500mL stream water were spiked with approx. 100, 1000 or 10,000 oocysts. To half of the wastewater and stream water 4mLL−1 of a 5% w/v MO seed extract was added, while the remaining water was left untreated. The water was stirred slowly for 20min and subsequently left to sediment for 15, 30, 45, 60 or 90min (wastewater) or 60min (stream water), with three (stream water) or six (wastewater) replicate glass jars representing each time point. In wastewater, MO seed extracts reduced the C. parvum oocyst load significantly (p=0.03) by 38% in the interval 15 to 90min compared to a 0.02% reduction in the untreated wastewater. Furthermore, the number of oocysts L−1 was significantly (p>0.0001–p=0.041) reduced in the treated wastewater at all five sampling times compared to untreated wastewater. Likewise, the oocyst loads in the supernatant of MO treated stream water were noticeably lower compared with untreated stream water at all three spikes. The turbidity was reduced to 10.9±0.3 Nephelometric turbidity units (NTU) (i.e. 94.7% reduction) and 13.7±2.1NTU (i.e. 91.7% reduction) in the treated wastewater and stream water, respectively. In contrast, the turbidity was 55.3±4.4NTU and 46.2±1.6NTU in untreated wastewater and stream water, respectively. M. oleifera seeds are readily available in many tropical countries where the tree is common, and our results clearly demonstrate that MO seed extract may be used by farmers for treatment of different types of surface water prior to irrigation use. Yet, adding MO seed extract to the low quality water did not successfully remove all oocyst. However, treatment of wastewater with MO seed extract significantly improved the water quality with regard to number of oocysts present and turbidity of the water. Further experiments with addition of higher concentrations of MO are needed to establish whether MO seed extract can be used to obtain safe irrigation water free of C. parvum oocysts and other protozoan parasites.

Deformability Assessment of Waterborne Protozoa Using a Microfluidic-Enabled Force Microscopy Probe.

Many modern filtration technologies are incapable of the complete removal of Cryptosporidium oocysts from drinking-water. Consequently, Cryptosporidium-contaminated drinking-water supplies can severely implicate both water utilities and consumers. Existing methods for the detection of Cryptosporidium in drinking-water do not discern between non-pathogenic and pathogenic species, nor between viable and non-viable oocysts. Using FluidFM, a novel force spectroscopy method employing microchannelled cantilevers for single-cell level manipulation, we assessed the size and deformability properties of two species of Cryptosporidium that pose varying levels of risk to human health. A comparison of such characteristics demonstrated the ability of FluidFM to discern between Cryptosporidium muris and Cryptosporidium parvum with 86% efficiency, whilst using a measurement throughput which exceeded 50 discrete oocysts per hour. In addition, we measured the deformability properties for untreated and temperature-inactivated oocysts of the highly infective, human pathogenic C. parvum to assess whether deformability may be a marker of viability. Our results indicate that untreated and temperature-inactivated C. parvum oocysts had overlapping but significantly different deformability distributions.

CryptosporidiumRemoval from Runoff by Active Carbon Filter with Coal Gangue

Transport ofCryptosporidiumin runoff will contaminate the surrounding water body.Cryptosporidium-sized microspheres and inactiveCryptosporidiumparvum oocysts removal using an active carbon (AC) filter with/without coal gangue from the runoff was evaluated. Chemical composition of coal gangue was determined, and its performance as a water treatment material was tested. Results showed SiO2was the dominant chemical component of coal gangue. Removal was only 20% for microspheres and 24% for oocysts by AC filtration alone. The removal for both was increased to more than 98% by addition of coal gangue powder to the filter. Furthermore, gangue reuse turned commercially worthless material to a water treatment material as well helping prevent gangue from occupying agriculture/industry land.

Removal of Cryptosporidium by wastewater treatment processes: a review

Cryptosporidium is a protozoan parasite that infects humans and various animal species. The environmental stability and the low infectious dose of Cryptosporidium facilitate its transmission by water and food. Discharge of untreated wastewater may result in waterborne or foodborne Cryptosporidium outbreaks, therefore a suitable treatment may prevent its dissemination. Most studies on the prevalence of Cryptosporidium oocysts in wastewater have reported a concentration range between 10 and 200 oocysts/L and a prevalence of 6 to 100%. Activated sludge has been found to be ineffective for the removal of Cryptosporidium oocysts. Stabilization ponds and constructed wetlands are efficient for the reduction of Cryptosporidium from wastewater, especially when the retention time is longer than 20 days at suitable sunlight and temperature. High rate filtration and chlorine disinfection are inefficient for the reduction of Cryptosporidium from effluents, whereas ultrafiltration and UV irradiation were found to be very efficient for the reduction of Cryptosporidium oocysts. Adequate tertiary treatment may result in high quality effluent with low risk of Cryptosporidium for unrestricted irrigation and other non-potable applications.

Effects of Drinking-Water Filtration onCryptosporidiumSeroepidemiology, Scotland

Continuous exposure to low levels of Cryptosporidium oocysts is associated with production of protective antibodies. We investigated prevalence of antibodies against the 27-kDa Cryptosporidium oocyst antigen among blood donors in 2 areas of Scotland supplied by drinking water from different sources with different filtration standards: Glasgow (not filtered) and Dundee (filtered). During 2006-2009, seroprevalence and risk factor data were collected; this period includes 2007, when enhanced filtration was introduced to the Glasgow supply. A serologic response to the 27-kDa antigen was found for ≈75% of donors in the 2 cohorts combined. Mixed regression modeling indicated a 32% step-change reduction in seroprevalence of antibodies against Cryptosporidium among persons in the Glasgow area, which was associated with introduction of enhanced filtration treatment. Removal of Cryptosporidium oocysts from water reduces the risk for waterborne exposure, sporadic infections, and outbreaks. Paradoxically, however, oocyst removal might lower immunity and increase the risk for infection from other sources.

Turbidity as a surrogate for Cryptosporidium removal by filtration in drinking-water QMRA models

A quantitative microbial risk assessment (QMRA) with Monte Carlo simulation was used to estimate risks of Cryptosporidium infection from drinking water. Four different approaches to assess Cryptosporidium oocyst removal by filtration were compared using three relationships between turbidity removal and oocyst removal proposed in the literature, and an empirical model based on oocyst log removal credits associated with filtered effluent turbidity. Using a large database of a full-scale water treatment plant in Brazil, two of the turbidity removal-based models returned 1–3 log unit removal of Cryptosporidium oocysts and median values of Cryptosporidium annual infection risk estimates of approximately 10−2pppy (per person per year). The other model based on turbidity removal and the empirical model resulted, respectively, in 2–3.5 and 0–4 log removal of Cryptosporidium oocysts and corresponding infection risk estimates around 10−2pppy, close therefore to the health-based targets of the WHO guidelines for drinking water. The results of this study indicate that the empirical model appears to be particularly suitable for QMRA studies and that similar models should be tested in other site-specific assessments of treatment performance.

Aggregation kinetics of Cryptosporidium parvum oocysts

Cryptosporidium parvum (C. parvum), an organism of increasing importance in drinking water, spreads to the environment through faeces of infected animals and humans. C. parvum produces infective chlorine-resistant oocyst that are removed from contaminated raw waters primarily using physical methods such as entrapment in surface or depth bed filters and coagulation–flocculation. In this paper, the aggregation properties of gamma-irradiated C. parvum oocysts in dilute concentrations, as a function of stirring time in the presence of bivalent and trivalent cations were studied. The size and surface charge of C. parvum oocysts were characterized before they were used for aggregation experiments. The surface charge of the oocysts, measured using a zeta potential analyzer were in the range of −57±2mV, which increased to −31±2mV in presence of bivalent electrolytes. Aggregation of oocyst in dilute suspensions was monitored using confocal laser scanning microscope (CLSM) in presence of bivalent or trivalent electrolytes. Aggregation was not visible in the diluted C. parvum oocyst suspension in Milli Q water system in the time frame of the experiment. Addition of a bivalent or trivalent salt with stirring condition induced aggregation due to the suppression of the surface charge of oocysts, resulting in a decrease in the energy of interaction between oocysts, and a decrease in double layer thickness around the oocysts. Predictive models could be built to understand C. parvum oocyst aggregation in raw waters, which could significantly improve the removal of oocysts from untreated (raw) drinking water.