The effect of UV irradiation on human-derived Giardia lamblia cysts

UV Disinfection sensitivity index of spores or protozoa: A model to predict the required fluence of spores or protozoa

During UV disinfection, the required UV dose in terms of fluence depends upon the species of bacteria spore and protozoa. To rank their UV disinfection sensitivity, spore sensitivity index (SPSI) and protozoan sensitivity index (PSI) are defined. For spores, shoulder effect exists, therefore, SPSI is defined as the ratio between the k_i of any spores for the linear portion of the dose response curve to the k_ir of Bacillus subtilis as the reference spore. After statistical analysis, the fluence of any spore can be predicted by SPSI through equation, H = (0.8358 ± 0.126)*LogI*SPSI + H₀. PSI is defined as the ratio between the inactivation rate constants of a protozoa in reference to that of Cryptosporidium parvum. The equation predicting the fluence of any protozoa in reference to Cryptosporidium parvum is: H = 107.45*(3.86 ± 2.68)*LogI/PSI. Two regression equations suggest that protozoa require significantly higher UV dose than bacteria spores.

CFDA-AM staining to assess the metabolic activity of Giardia duodenalis cysts inactivated by chlorine, boiling and ultraviolet irradiation

Giardia duodenalis is responsible for several waterborne gastrointestinal outbreaks worldwide. In addition to limitations presented by the main disinfection methods, assessing the inactivation efficiency of cysts after the treatment also poses challenges. Thus, this study aimed to use the 5-carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM) staining protocol to evaluate the viability of G. duodenalis cysts inactivated by different UV and chlorination doses and boiling times. Under epifluorescent microscopy, metabolically active cysts that presented green fluorescence were considered viable. In contrast, when no green fluorescence could be observed, organisms were considered non-viable. Although statistical analysis revealed that increasing the UV dose did not significantly decrease the percentage of viable cysts, the fluorescence signal intensity decreased considerably when the cysts were irradiated with a dose equal to or greater than 80 mJ cm^-2. Regarding chlorination and boiling treatments, this study demonstrated that no cyst showed fluorescence at the lowest NaClO concentration (0.5 mg/L) and in the shortest boiling time (2 min). Despite some limitations regarding the use of metabolic activity as a viability marker, this methodology is rapid, easy to run and cost-effective. Thus, we conclude that the CFDA-AM staining protocol has the potential to be used to assess Giardia cyst inactivation, although further research is required.

Efficiency of chlorine and UV in the inactivation of Cryptosporidium and Giardia in wastewater

Wastewater from different sources is contaminated by protozoan parasites including Cryptosporidium and Giardia. Many protozoan parasites are becoming resistant to chemical treatment. The challenge of finding alternatives is presented to researchers by exploring other methods of eliminating protozoan parasites from wastewater. The aim of this study was to assess the speciation and the viability of Cryptosporidium and Giardia in environmental samples with the specific objective of evaluating if effluent chlorination and UV affect the viability. Different doses of chlorine with different exposure times were experimented with both distilled water and waste water spiked with (oo)cysts derived from environmental samples. UV irradiation at different doses was also experimented using the same spiked samples. Two methods of quantification and detection, namely, microscopy and flow cytometry, were used in the experiment. Two vital dyes, Syto-9+PI and DAPI+PI, were the used for staining the collected wastewater samples. It was found that the (oo)cysts responded to chlorination and UV treatments with Giardia responding better than Cryptosporidium. Giardia responded very well to UV irradiations with almost 0 percent remaining viable after a low dose of UV. Cryptosporidium was found to be resistant to chlorination even at high doses but responded well to high UV doses. DAPI+PI dye gave a lower mean percentage viability values than Syto-9+PI. Flow cytometry gave higher mean percentage than microscopy from the results. It is concluded that UV is a promising alternative to Chlorine in removing Cryptosporidium and Giardia from waste water. Appropriate treatment method for wastewater is necessary to minimize water resources pollution when wastewater is released into water systems.

The Biological Basis for Ballast Water Performance Standards: "Viable/Non-Viable" or "Live/Dead"?

The shipping industry is critical to international commerce; however, contemporary shipping practices involve uptake and discharge of ballast water, which introduces the potential for transfer of nonindigenous, invasive species among geographically distinct habitats. To counteract this hazard, regulations for ballast water management have been implemented by the International Maritime Organization (IMO) and by regulatory agencies such as the United States Coast Guard (USCG). IMO and USCG discharge standards are numerically identical, but involve different definitions of treatment end points, which are based on fundamentally different biological assays for quantification of ballast water treatment effectiveness. Available assays for quantification of the responses of organisms in the 10-50 μm size range include vital stains based on fluorescein diacetate (FDA), sometimes used in combination with 5-chloromethylfluorescein diacetate (CMFDA), observations of motility, and the most probable number dilution culture method (MPN). The mechanisms and implications of these assays are discussed relative to the Type Approval process, which quantitatively evaluates compliance with ballast water discharge standards (BWDSs) under controlled shipboard and land-based tests. For antimicrobial processes that accomplish treatment by preventing subsequent replication of the target species, the FDA/CMFDA and MPN methods can yield dramatically different results. An important example of a treatment process that is affected by the choice of assay is ultraviolet (UV) irradiation. Results of laboratory and field experiments have demonstrated UV-based technologies to be effective for accomplishing the objectives of ballast water treatment (inactivation of cellular reproduction), when the MPN assay is used as the basis for evaluation. The FDA, CMFDA, motility, and MPN methods are subject to well recognized sources of error; however, the MPN method is based on a response that is consistent with the objectives of ballast water management as well as the mechanism of action of UV-based inactivation. Complementary assays are available for use in compliance testing; however, the development of relevant indicative tests remains as a research priority. Historical lessons learned from applications of vital stains (and other indirect methods) for quantification of microbial responses to UV irradiation in other settings also support the use of assays that provide a direct measure of growth and reproduction, such as MPN. Collectively, these observations point to the use of MPN assays as the standard for type testing, especially when UV-based treatment is employed.

Assessing viability and infectivity of foodborne and waterborne stages (cysts/oocysts) of Giardia duodenalis, Cryptosporidium spp., and Toxoplasma gondii: a review of methods

Giardia duodenalis, Cryptosporidium spp. and Toxoplasma gondii are protozoan parasites that have been highlighted as emerging foodborne pathogens by the Food and Agriculture Organization of the United Nations and the World Health Organization. According to the European Food Safety Authority, 4786 foodborne and waterborne outbreaks were reported in Europe in 2016, of which 0.4% were attributed to parasites including Cryptosporidium, Giardia and Trichinella. Until 2016, no standardized methods were available to detect Giardia, Cryptosporidium and Toxoplasma (oo)cysts in food. Therefore, no regulation exists regarding these biohazards. Nevertheless, considering their low infective dose, ingestion of foodstuffs contaminated by low quantities of these three parasites can lead to human infection. To evaluate the risk of protozoan parasites in food, efforts must be made towards exposure assessment to estimate the contamination along the food chain, from raw products to consumers. This requires determining: (i) the occurrence of infective protozoan (oo)cysts in foods, and (ii) the efficacy of control measures to eliminate this contamination. In order to conduct such assessments, methods for identification of viable (i.e. live) and infective parasites are required. This review describes the methods currently available to evaluate infectivity and viability of G. duodenalis cysts, Cryptosporidium spp. and T. gondii oocysts, and their potential for application in exposure assessment to determine the presence of the infective protozoa and/or to characterize the efficacy of control measures. Advantages and limits of each method are highlighted and an analytical strategy is proposed to assess exposure to these protozoa.

Parasite contamination of berries: Risk, occurrence, and approaches for mitigation

Fresh fruits and vegetables, including berries, are essential components of a healthy diet and are relevant in the prevention of chronic non-communicable diseases such as cancer and heart disease. Associations between diet and health are becoming an increasing focus of consumers, and, in response, consumption of fresh berries has been increasing rapidly in recent decades. However, increased consumption of berries may be associated with an increased risk of acquiring foodborne infections, including parasites. In this review, we describe how parasite contamination of berries may occur at several points on the farm-to-fork pathway, starting from the use of contaminated water for irrigation and pesticide application, and contact with animal and human faeces during cultivation, through contaminated harvesting equipment, and including unhygienic practices of berry pickers in the production field or others handling berries prior to consumption. Parasite transmission stages tend to be robust and therefore likely to survive from contamination in the field, through the various stages of harvesting, packaging, and sale, until consumption. We describe outbreaks of parasitic disease associated with consumption of berries - so far only described for Cyclospora and Trypanosoma cruzi, both of which are briefly introduced - but also show from survey data summarised in this review that sporadic infections or undetected outbreaks associated with contaminated berries may also occur. In addition, we describe methods for assessing whether berries are contaminated with parasite transmission stages, with emphasis on the challenges associated with analysing this particular matrix. Emphasis on current possibilities for mitigation and control are addressed; avoidance of contamination and implementation of good management practices and a hazard analysis and critical control points (HACCP) approach are essential.

Reactivation of Giardia lamblia cysts after exposure to low-pressure UV irradiation

In this study, we determined the repair capabilities of Giardia lamblia cysts when they were exposed to low-pressure (LP) UV and then 4 different repair conditions. A UV collimated beam apparatus was used to expose shallow suspensions of G. lamblia cysts in buffered reagent water (PBS, pH 7.2) to various doses of LP UV irradiation. After UV irradiation, samples were exposed to 4 repair conditions (light and dark repair conditions with 2 temperatures (25 °C and 37 °C) for each condition). The inactivation of G. lamblia cysts by LP UV was very extensive (∼ 5 log10) even with a low dose of LP UV (1 mJ/cm(2)). More importantly, there was significant restoration of infectivity in G. lamblia cysts when they were exposed to a low dose of LP UV and then to all the repair conditions tested. Overall, the results of this study indicate that G. lamblia cysts do have the ability to repair their UV-damaged DNA when they are exposed to low doses of LP UV irradiation. This is the first study to report the presence of repair in UV-irradiated G. lamblia cysts.

Development of a combined in vitro cell culture--quantitative PCR assay for evaluating the disinfection performance of pulsed light for treating the waterborne enteroparasite Giardia lamblia

Giardia lamblia is a flagellated protozoan parasite that is recognised as a frequent cause of water-borne disease in humans and animals. We report for the first time on the use of a combined in vitro HCT-8 cell culture-quantitative PCR assay for evaluating the efficacy of using pulsed UV light for treating G. lamblia parasites. Findings showed that current methods that are limited to using vital stains before and after cyst excystation are not appropriate for monitoring or evaluating cyst destruction post PUV-treatments. Use of the human ileocecal HCT-8 cell line was superior to that of the human colon Caco-2 cell line for in vitro culture and determining PUV sensitivity of treated cysts. G. lamblia cysts were also shown to be more resistant to PUV irradiation compared to treating similar numbers of Cryptosporidium parvum oocysts. These observations also show that the use of this HCT-8 cell culture assay may replace use of animal models for determining disinfection performances of PUV for treating both C. parvum and G. lamblia.

Point-of-use water disinfection using UV light-emitting diodes to reduce bacterial contamination

The treatment process described in this research explores the impact of exposing water samples containing fecal coliforms to the radiation produced by single ultraviolet (UV) light-emitting diodes (LEDs) operating at 265 nm. UV LEDs are long lasting, compact in size and produce more efficient light output than traditional mercury-vapour bulbs, making them ideal for application in point-of-use disinfection systems, such as in remote areas. In this study, contaminated water samples containing either a pure culture of Escherichia coli or tertiary effluent from the City of Regina Wastewater Treatment Plant were used to study the application and efficiency of using UV LEDs for water disinfection. The results indicate that bacterial inactivation was achieved in a time-dependent manner, with 1- and 2.5-log E. coli reductions in water following 20 and 50 min of UV LED exposure, respectively. Ultraviolet radiation was less effective in reducing coliform bacteria in wastewater samples due to the elevated turbidity levels. Further work remains to be completed to optimize the application of UV LEDs for point-of-use disinfection systems; however, the results from this study support that bacterial inactivation using UV LEDs is possible, meriting further future technological development of the LEDs.

Infectivity of Giardia duodenalis Cysts from UV Light-Disinfected Wastewater Effluent Using a Nude BALB/c Mouse Model

Giardia duodenalis is a protozoan of public health interest that causes gastroenteritis in humans and other animals. In the city of Campinas in southeast Brazil, giardiasis is endemic, and this pathogen is detected at high concentrations in wastewater effluents, which are potential reservoirs for transmission. The Samambaia wastewater treatment plant (WWTP) in the city of Campinas employs an activated sludge system for sewage treatment and ultraviolet (UV) light for disinfection of effluents. To evaluate this disinfection process with respect to inactivating G. duodenalis cysts, two sample types were investigated: (i) effluent without UV disinfection (EFL) and (ii) effluent with UV disinfection (EFL+UV). Nude immunodeficient BALB/c mice were intragastrically inoculated with a mean dose of 14 cysts of G. duodenalis recovered from effluent from this WWTP, EFL, or EFL+UV. All animals inoculated with G. duodenalis cysts developed the infection, but animals inoculated with UV-exposed cysts released a lower average concentration of cysts in their faeces than animals inoculated with cysts that were not UV disinfected. Trophozoites were also observed in both groups of animals. These findings suggest that G. duodenalis cysts exposed to UV light were damaged but were still able to cause infection.

Inactivation of Giardia lamblia cysts by polychromatic UV

AIMS

Giardia lamblia is one of the most important waterborne pathogens in the world. In this study, we determined the effectiveness of a promising alternative UV technology - a polychromatic emission from a medium-pressure (MP) UV lamp - against G. lamblia cysts in phosphate buffered saline (PBS) and a filtered drinking water.

METHODS AND RESULTS

A UV collimated beam apparatus was used to expose shallow suspensions of purified G. lamblia cysts in PBS or a filtered drinking water and the UV-irradiated G. lamblia cysts were assayed in Mongolian gerbils. The inactivation of G. lamblia cysts was very rapid and reached a detection limit of >3 log(10) within a UV dose of 1 mJ cm(-2).

CONCLUSION

The results of this study indicate that MP UV irradiation is very effective against G. lamblia cysts in both PBS and a filtered drinking water.

SIGNIFICANCE AND IMPACT OF THE STUDY

It is likely that contamination of drinking water by G. lamblia cysts can be readily controlled by typical MP UV disinfection practises.

Comparison of levels of inactivation of two isolates of Giardia lamblia cysts by UV light

The effects of 254-nm UV irradiation on two human isolates (WB and H3) of Giardia lamblia cysts were assessed using a collimated beam protocol and a Mongolian gerbil model. The levels of infection of cysts in the gerbils were assessed based on the presence of cysts in feces and the presence and activity of trophozoites in the small intestine of inoculated gerbils. The results suggest that there were differences in the infectivities of the WB and H3 isolates, as well as in susceptibilities of the parasites to UV light. Without UV exposure, gerbils were more readily infected by isolate H3 cysts. After UV exposure of the cysts, however, the gerbils were more susceptible to isolate WB cysts.

Inactivation of protozoan parasites in food, water, and environmental systems

Protozoan parasites can survive under ambient and refrigerated storage conditions when associated with a range of substrates. Consequently, various treatments have been used to inactivate protozoan parasites (Giardia, Cryptosporidium, and Cyclospora) in food, water, and environmental systems. Physical treatments that affect survival or removal of protozoan parasites include freezing, heating, filtration, sedimentation, UV light, irradiation, high pressure, and ultrasound. Ozone is a more effective chemical disinfectant than chlorine or chlorine dioxide for inactivation of protozoan parasites in water systems. However, sequential inactivation treatments can optimize existing treatments through synergistic effects. Careful selection of methods to evaluate inactivation treatments is needed because many studies that have employed vital dye stains and in vitro excystation have produced underestimations of the effectiveness of these treatments.

Ultraviolet light inactivation of protozoa in drinking water: a Bayesian meta-analysis

To assess the dose of UV light needed to achieve specified levels of Giardia spp. cysts and Cryptosporidium spp. oocysts inactivation in drinking water, a Bayesian meta-analysis is used to analyze experimental data from several studies. Of the 20 studies identified by an extensive data collection effort, 14 (five reported experiments on Giardia and nine on Cryptosporidium) were selected for analysis based on a set of criteria. A substantial amount of the log inactivation data are reported as greater than a given inactivation level (i.e., censored data). The Bayesian hierarchical modeling approach used in this study not only properly addresses the common concerns in a meta-analysis but also provides a robust method for incorporating censored data. Different statistical models will result in different estimates of the UV doses needed to achieve a specific inactivation level. The Bayesian approach allows us to present the uncertainty in terms of risk, which is better suited for supporting US EPA in developing regulations.