Efficacy of activated sludge in removing Cryptosporidium parvum oocysts from sewage

Wastewater-based epidemiology-surveillance and early detection of waterborne pathogens with a focus on SARS-CoV-2, Cryptosporidium and Giardia

Waterborne diseases are a major global problem, resulting in high morbidity and mortality, and massive economic costs. The ability to rapidly and reliably detect and monitor the spread of waterborne diseases is vital for early intervention and preventing more widespread disease outbreaks. Pathogens are, however, difficult to detect in water and are not practicably detectable at acceptable concentrations that need to be achieved in treated drinking water (which are of the order one per million litre). Furthermore, current clinical-based surveillance methods have many limitations such as the invasive nature of the testing and the challenges in testing large numbers of people. Wastewater-based epidemiology (WBE), which is based on the analysis of wastewater to monitor the emergence and spread of infectious disease at a population level, has received renewed attention in light of the current coronavirus disease 2019 (COVID-19) pandemic. The present review will focus on the application of WBE for the detection and surveillance of pathogens with a focus on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the waterborne protozoan parasites Cryptosporidium and Giardia. The review highlights the benefits and challenges of WBE and the future of this tool for community-wide infectious disease surveillance.

Efficacy of chitosan, a natural polysaccharide, against Cryptosporidium parvum in vitro and in vivo in neonatal mice

Cryptosporidiosis is a zoonotic disease caused by species in the genus Cryptosporidium. In young ruminants, Cryptosporidium parvum causes economically significant disease with mild to severe clinical signs and occasional death. The typical clinical course in animals aged 1-3 weeks old is acute diarrhoea. Currently there are no available treatments that are fully effective against cryptosporidiosis in either humans or animals. Therefore there is a critical need for the development of new therapeutic agents. We adapted two in vitro culture systems (HCT-8 and Caco-2 cell lines) for C. parvum infection to investigate the "anticryptosporidial" activity of two chitosans; Chitosan NAG and Chitosan Mix. Chitosan-a naturally-occurring polysaccharide compound-has been found to be active against a variety of diseases, possessing both antimicrobial and anticancer properties. We investigated both chitosan's toxicity and effects on C. parvum in the two in vitro models. To evaluate chitosan's effects on oocyst shedding in vivo, CD-1 neonate mice were orally inoculated with C. parvum oocysts (Iowa strain), treated with chitosan, and compared to infected non-treated animals. Paromomycin, a classical drug used in veterinary medicine, was used as a reference compound. Immunofluorescence techniques were used to analyse the parasites. Our results showed significant reductions in Cryptosporidium oocyst viability (>95%) after oocyst pre-incubation with either paromomycin (P < 0.001), Chitosan Mix or Chitosan NAG (P < 0.001), for 24 h at 37 °C. Additionally, paromomycin, Chitosan Mix, and Chitosan NAG significantly inhibited C. parvum multiplication in HCT-8 and Caco-2 cell lines (P < 0.005). These effects were dose-dependent. In in vivo studies, treatment with both chitosans (Chitosan NAG, Chitosan Mix) or paromomycin sulfate significantly reduced parasite shedding in infected treated newborn mice (-56%, -34.5% and -58%, respectively). In conclusion, these findings provide the first in vitro and in vivo evidence of the anticryptosporidial activities of this natural polysaccharide.

Contribution of treated wastewater to the contamination of recreational river areas with Cryptosporidium spp. and Giardia duodenalis

Samples of the influent and final effluent from 12 wastewater treatment plants from Galicia (NW, Spain) were analyzed for the presence of Cryptosporidium spp. oocysts and Giardia duodenalis cysts. All of the plants discharge effluent to a hydrographic basin in which there are numerous recreational areas and fluvial beaches. The samples (25-50 liters) were collected in spring, summer, autumn and winter of 2007. A total of 96 samples were analyzed using techniques included in the US Environmental Protection Agency Method 1623. To identify the genotypes present, the following genes were amplified and sequenced: 18S SSU rRNA (Cryptosporidium spp.) and beta-giardina (G. duodenalis). Both parasites were detected in influent and effluent samples from all treatment plants (100%) throughout the year, and G. duodenalis always outnumbered Cryptosporidium spp. The mean concentration of G. duodenalis per liter of influent was significantly higher (P<0.05) than the mean concentration of Cryptosporidium spp. per liter of influent. The mean concentrations of parasites in influent samples ranged from 6 to 350 Cryptosporidium spp. oocysts per liter and from 89 to 8305 G. duodenalis cysts per liter. In final treated effluent, the mean concentration of parasites ranged from 2 to 390 Cryptosporidium spp. oocysts per liter and from 79 to 2469 G. duodenalis cysts per liter. The distribution of results per season revealed that in all plants, the highest number of (oo)cysts were detected in spring and summer. Cryptosporidium parvum, Cryptosporidium andersoni, Cryptosporidium hominis and assemblages A-I, A-II, E of G. duodenalis were detected. The risk of contamination of water courses by Cryptosporidium spp. and G. duodenalis is therefore considerable. It is important that wastewater treatment authorities reconsider the relevance of the levels of contamination by both parasites in wastewater, and develop adequate countermeasures.

The role of wastewater treatment in protecting water supplies against emerging pathogens

Traditionally, regulators, dischargers, and even water suppliers believed that wastewater discharge meeting the levels of 200 cfu/ 100 mL of fecal coliforms in wastewater effluent was sufficient to protect against downstream microbial effects. However, these beliefs are now being challenged by emerging pathogens that are resistant to standard water and wastewater treatment processes, exhibit extended survival periods in the environment, can adversely affect sensitive subpopulations, and require extremely low doses for human infection. Based on this new information, it is estimated that discharges of emerging pathogens from conventional wastewater treatment plants as far as 160 km upstream and cumulative amounts of wastewater discharge ranging from 2 to 20 ML/d have the potential to reach a water supply intake in a viable state at significant concentrations that could exceed regulatory limits for drinking water supplies, increase endemic risk from drinking water, and/or require additional drinking water treatment. Wastewater dischargers may be able mitigate this potential effect and achieve upwards of 6 log combined removal and inactivation of emerging pathogens to mitigate drinking water effects by using alternative treatment processes, such as filtration or UV light disinfection, or optimizing these processes based on site-specific conditions.

Cryptosporidium contamination in harvesting areas of bivalve molluscs

Cryptosporidium contamination was evaluated in areas in Galicia (northwestern Spain) where bivalve molluscs are harvested. Galicia is the main mussel-producing region in Europe. Data were collected on water contamination of effluents that are discharged into these areas. Cryptosporidium spp. were detected by immunofluorescence microscopy and molecular methods in 71% of the river water samples (n = 7), 64% of raw sewage samples (n = 11), 50% of effluents from wastewater treatment plants (n = 16), and 29.3% of the mussel samples (Mytilus galloprovincialis, n = 184). Cryptosporidium parvum was identified in all samples of contaminated mussels, Cryptosporidium muris was found in three samples of effluent from wastewater treatment plants, and Cryptosporidium baileyi was found in a sample of raw sewage. Further studies are needed to determine the parasitological quality of water in these shellfish harvesting and recreational areas. Cryptosporidium could be a public health risk from consumption of raw or undercooked contaminated molluscs and use of contaminated waters for recreational purposes.

Giardia in shellfish-farming areas: Detection in mussels, river water and waste waters

Giardia cyst contamination of mussels (Mytilus galloprovincialis), raw and treated waste waters and water from rivers that flow into four Galician estuaries (NW Spain), where bivalve molluscs are cultured for human consumption, was studied. The high prevalence of contamination in mussels (41.8%, n=184), raw waste water (90.9%, n=11), treated waste water (87.5%, n=16) and in samples of river water (85.7%, n=7), with cyst counts of 9.8-1800.0, 7.0-2541.0 and 1.0-29.3 cysts l(-1), respectively, illustrate the wide distribution of this enteropathogen in the environment and the potential risk to public health associated with the consumption of raw or undercooking bivalves and use of these estuaries for recreational purposes.

Using event trees to quantify pathogen levels on root crops from land application of treated sewage sludge

AIMS

To quantify the incremental exposure of root crops, at point of harvest, to enteric pathogens from sewage sludge applied to agricultural land according to current regulations and guidance (Safe Sludge Matrix).

METHODS AND RESULTS

A quantitative risk assessment based on the Source-Pathway-Receptor approach is developed for Cryptosporidium and salmonellas. Event trees are constructed to model the partitioning of pathogens present in raw sewage into sludge at the sewage treatment works and to model to the pathways by which root crops may be exposed to those pathogens after treatment and land application of the sludge. The main barriers are sewage sludge treatment, and decay and dilution of the pathogens in the soil. The exposures are expressed in terms of the arithmetic mean. This represents the total loading and accommodates fluctuations not only in the levels of pathogens present in sewage but also in the removal efficiencies by the various barriers. One source of uncertainty is the degree of by-pass of sludge treatment at operational scale.

CONCLUSIONS

The models predict that land application of sewage sludge treated by conventional processes (achieving 2-log removal) increases the exposures of root crops to salmonellas and Cryptosporidium oocysts by counts of 0.070 and 0.033 kg(-1), respectively. These predictions are based on decay periods in the soil of 5 and 12 weeks, respectively, and are therefore worst case in not allowing for the full extent of no harvesting periods. A Monte Carlo simulation predicts that 0.01% of 1-kg batches contained > 50 salmonellas and demonstrates that, for risk assessment, it is acceptable to use the arithmetic mean exposure directly in the dose-response curve.

SIGNIFICANCE AND IMPACT OF THE STUDY

The predicted numbers of pathogens on root crops at point of harvest provide a basis for modelling the excess risks to humans consuming such crops. The approach underpins scientifically the Safe Sludge Matrix.

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.

Effect of salinity, temperature and storage time on mouse experimental infection by Cryptosporidium parvum

Cryptosporidium parvum oocysts collected from a naturally infected calf were exposed to different salinity and temperature for 2, 21 and 40 days, and then inoculated intragastrically into coccidium-free neonatal mice. The intensity of infection as determined seven days later by examination of intestinal homogenates were statistically analysed. Salinity, time and salinity-time interaction were the only factors with significant effect on the infection intensity.

Environmental ecology of Cryptosporidium and public health implications

Cryptosporidium has become the most important contaminant found in drinking water and is associated with a high risk of waterborne disease particularly for the immunocompromised. There have been 12 documented waterborne outbreaks in North America since 1985; in two of these (Milwaukee and Las Vegas) mortality rates in the immunocompromised ranged from 52% to 68%. The immunofluorescence antibody assay (IFA) using epifluorescence microscopy has been used to examine the occurrence of Cryptosporidium in sewage (1 to 120 oocysts/liter), filtered secondary treated wastewater (0.01 to 0.13 oocysts/liter), surface waters (0.001 to 107 oocysts/liter), groundwater (0.004 to 0.922 oocysts/liter) and treated drinking water (0.001 to 0.72 oocysts/liter). New rules are being developed (Information Collection Rule and Enhanced Surface Water Treatment Rule) to obtain more occurrence data for drinking water systems for use with new risk assessment models. Public health officials should consider a communication program to physicians treating the immunocompromised, nursing homes, develop a plan to evaluate cases of cryptosporidiosis in the community, and contribute to the development of public policies that limit contamination of source waters, improve water treatment, and protect public health.

The effect of sewage sludge treatment processes on oocysts of Cryptosporidium parvum

The effect of common sewage sludge treatment processes on oocysts of the coccidian protozoan Cryptosporidium was evaluated in laboratory simulations. The ability of primary sewage sedimentation to remove Cryptosporidium oocysts was found to be poor. Thermophilic (55 degrees C) aerobic digestion and sludge pasteurization at the same temperature were found to be effective treatments to inactivate Cryptosporidium oocysts. Approximately 10% of the oocyst population were found to be viable after 18 d exposure to mesophilic (35 degrees C) anaerobically digesting sludge. The viability of Cryptosporidium oocysts decreased within the range 20-40% in sludge-treated soil mesocosms over 30 d. The survival results obtained, however, indicated that oocysts would survive well beyond this period.