Oral inoculation of ultraviolet-irradiated Eimeria species oocysts protects chickens against coccidiosis

Prevention of coccidiosis is one of the best ways of controlling disease. Therefore, the present study was carried out to evaluate the protective effect of ultraviolet (UV)-irradiated sporulated oocysts of Eimeria species against coccidiosis in layer chickens. One hundred forty-four one-day-old layer chicks were randomly divided into 4 groups (n = 36), including non-immunized/non-challenged negative control group (NC group), non-immunized/challenged control group (NIC group), non-irradiated sporulated oocyst/challenged group (CA group), and UV-irradiated sporulated oocyst/challenged (UV group). At the age of 4 days, chickens in groups UV and CA were both orally inoculated with 1.0 × 10⁴ UV-irradiated and non-irradiated sporulated oocysts of Eimeria species, respectively. Chickens in groups NIC and NC were served as positive and negative controls, respectively. Chickens in all groups were orally challenged with 7.5 × 10⁴ sporulated oocysts of Eimeria species except the NC group at the age of 21 days. The results revealed that chicks receiving UV-irradiated sporulated oocysts had no signs of illness with minimal or no changes in the cecal integrity and a significantly lower oocyst shedding (OPG) than in the NIC group. Additionally, the cytokine gene expression profiles were evaluated. Expression levels of IL-2, IL-12, and IFN-γ were significantly higher in the spleen of chicks in the UV and CA groups than in the NC group post-challenge. As expected, treatment with irradiated oocysts resulted in a significant reduction in oocyst shedding and maintenance of cecal mucosal integrity. Furthermore, the body weight was higher in chickens inoculated with UV-irradiated oocysts than their non-irradiated counterparts. In conclusion, our results demonstrate that inoculation with UV-irradiated sporulated oocysts of Eimeria species can produce a substantial reduction in infection symptoms.

Urban water reuse: microbial pathogens control by direct filtration and ultraviolet disinfection

Physicochemical treatment efficiency for unrestricted urban water reuse was evaluated at a conventional activated-sludge wastewater treatment plant (WWTP). Pilot plant set-up consisted of an alum coagulation step, granular media upflow flocculation and direct downflow dual-media filtration followed by ultraviolet disinfection (dose of 95 mJ cm⁻²). Optimum aluminum sulfate dosage of 10 mg L⁻¹ and coagulation pH 7.0 were preset based on bench scale tests. Under WWTP stable operation, water quality met United States Environmental Protection Agency (USEPA) suggested guidelines for unrestricted urban reuse regarding turbidity (mean value 1.3 NTU) and suspended solids (mean value 2.1 mg L⁻¹). When WWTP overall plant performance dropped from 90 to 80% (although BOD value stayed below 6 mg O₂ L⁻¹, suggesting unrestricted reuse), solids breakthrough in filtrate was observed. Microorganism removal rates were: total coliforms 60.0%, Escherichia coli 63.0%, Giardia spp. 81.0%, and helminth eggs 62.5%; thus organisms still remained in filtrate. Ultraviolet (UV) disinfection efficiency was 4.1- and 3.8-log for total coliforms and E. coli, respectively. Considering low UV efficiency obtained for helminths and the survival of protozoa and helminths in the environment, effluent quality presents risk to public health if destined for unrestricted urban reuse.

Direct and indirect QMRA of infectious Cryptosporidium oocysts in reclaimed water

Water scarcity leads to an increased use of reclaimed water, which in turn calls for an improvement in water reclamation procedures to ensure adequate quality of the final effluent. The presence of infectious Cryptosporidium oocysts (IOO) in reclaimed water is a health hazard for users of this resource. Here, we gathered information on Cryptosporidium (concentrations, infectivity and genotype) in order to perform quantitative microbial risk assessment (QMRA). Moreover, data concerning the spores of sulphite-reducing clostridia (SRC) were used to undertake QMRA at a screening level. Our results show that the probability of infection (PI) by Cryptosporidium depends on the tertiary treatment type. The mean PI using the exponential dose-response model was 3.69 × 10(-6) in tertiary effluents (TE) treated with UV light, whereas it was 3 log(10) units higher, 1.89 × 10(-3), in TE not treated with this disinfection method. With the β-Poisson model, the mean PI was 1.56 × 10(-4) in UV-treated TE and 2 log(10) units higher, 4.37 × 10(-2), in TE not treated with UV. The use of SRC to perform QMRA of Cryptosporidium showed higher PI than when using directly IOO data. This observation suggests the former technique is a conservative method of QMRA.

Biofilms reduce solar disinfection of Cryptosporidium parvum oocysts

Solar radiation reduces Cryptosporidium infectivity. Biofilms grown from stream microbial assemblages inoculated with oocysts were exposed to solar radiation. The infectivity of oocysts attached at the biofilm surface and oocysts suspended in water was about half that of oocysts attached at the base of a 32-μm biofilm.

Inactivation of Ascaris eggs in water using sequential solar driven photo-Fenton and free chlorine

Sequential helminth egg inactivation using a solar driven advanced oxidation process (AOP) followed by chlorine was achieved. The photo-assisted Fenton process was tested alone under different H(2)O(2) and/or Fe(II) concentrations to assess its ability to inactivate Ascaris suum eggs. The effect of free chlorine alone was also tested. The lowest egg inactivation results were found using Fe(II) or H(2)O(2) separately (5 and 140 mmol L(-1), respectively) in dark conditions, which showed about 28% inactivation of helminth eggs. By combining Fe(II) and H(2)O(2) at the same concentrations described earlier, 55% of helminth egg inactivation was achieved. By increasing the reagent's concentration two-fold, 83% egg inactivation was achieved after 120 min of reaction time. Process efficiency was enhanced by solar excitation. Using solar disinfection only, the A. suum eggs inactivation reached was the lowest observed (58% egg inactivation after 120 min (120 kJ L(-1))), compared with tests using the photo-Fenton process. The use of the photo-Fenton reaction enhanced the process up to over 99% of egg inactivation after 120 kJ L(-1) when the highest Fe(II) and H(2)O(2) concentration was tested. Practically no effect on the helminth eggs was observed with free chlorine alone after 550 mg min L(-1) was used. Egg inactivation in the range of 25-30% was obtained for sequential processes (AOP then chlorine) using about 150 mg min L(-1).

Evaluation of the solar water disinfection process (SODIS) against Cryptosporidium parvum using a 25-L static solar reactor fitted with a compound parabolic collector (CPC)

Water samples of 0, 5, and 30 nephelometric turbidity units (NTU) spiked with Cryptosporidium parvum oocysts were exposed to natural sunlight using a 25-L static solar reactor fitted with a compound parabolic collector (CPC). The global oocyst viability was calculated by the evaluation of the inclusion/exclusion of the fluorogenic vital dye propidium iodide and the spontaneous excystation. After an exposure time of 8 hours, the global oocyst viabilities were 21.8 ± 3.1%, 31.3 ± 12.9%, and 45.0 ± 10.0% for turbidity levels of 0, 5, and 30 NTU, respectively, and these values were significantly lower (P < 0.05) that the initial global viability of the isolate (92.1 ± 0.9%). The 25-L static solar reactor that was evaluated can be an alternative system to the conventional solar water disinfection process for improving the microbiological quality of drinking water on a household level, and moreover, it enables treatment of larger volumes of water (> 10 times).

Determining UV inactivation of Toxoplasma gondii oocysts by using cell culture and a mouse bioassay

The effect of UV exposure on Toxoplasma gondii oocysts has not been completely defined for use in water disinfection. This study evaluated UV-irradiated oocysts by three assays: a SCID mouse bioassay, an in vitro T. gondii oocyst plaque (TOP) assay, and a quantitative reverse transcriptase real-time PCR (RT-qPCR) assay. The results from the animal bioassay show that 1- and 3-log(10) inactivation is achieved with 4 mJ/cm(2) UV and 10 mJ/cm(2) low-pressure UV, respectively. TOP assay results, but not RT-qPCR results, correlate well with bioassay results. In conclusion, a 3-log(10) inactivation of T. gondii oocysts is achieved by 10-mJ/cm(2) low-pressure UV, and the in vitro TOP assay is a promising alternative to the mouse bioassay.

Photocatalytic inactivation of Cryptosporidium parvum on nanostructured titanium dioxide films

Control of waterborne gastrointestinal parasites represents a major concern to water industries worldwide. In developed countries, pathogens in drinking water supplies are normally removed by sand filtration followed by chemical disinfection. Cryptosporidium spp. are generally resistant to common disinfection techniques and alternative control strategies are being sought. In the current study, the photocatalytic inactivation of C. parvum oocysts was shown to occur in buffer solution (78.4% after 180 min) and surface water (73.7% after 180 min). Viability was assessed by dye exclusion, excystation, direct examination of oocysts and a novel gene expression assay based on lactate dehydrogenase 1 (LDH1) expression levels. Collectively, this confirmed the inactivation of oocysts and scanning electron microscopy (SEM) confirmed cleavage at the suture line of oocyst cell walls, revealing large numbers of empty (ghost) cells after exposure to photocatalytic treatment.

Environmental inactivation of Cryptosporidium parvum oocysts in waste stabilization ponds

The survival of Cryptosporidium parvum oocysts in a waste stabilization pond system in northwestern Spain and the effects of sunlight and the depth and type of pond on oocyst viability were evaluated using an assay based on the exclusion or inclusion of two fluorogenic vital dyes, 4',6-diamidino-2-phenylindole (DAPI) and propidium iodide (PI). All tested factors had significant effects (P < 0.01) over time on C. parvum oocyst viability. Sunlight exposure was the most influential factor for oocyst inactivation. A 40% reduction was observed after 4 days exposure to sunlight conditions compared with dark conditions. The type of pond also caused a significant reduction in C. parvum oocyst viability (P < 0.01). Inactivation rates reflected that the facultative pond was the most aggressive environment for oocysts placed both at the surface (presence of sunlight) and at the bottom (absence of sunlight) of the pond, followed by the maturation pond and the anaerobic pond. The mean inactivation rates of oocysts in the ponds ranged from 0.0159 to 0.3025 day(-1).

Pulsed-UV light inactivation of Cryptosporidium parvum

Cryptosporidium parvum is an organism that threatens public health in the water industry. It is critical to develop improved detection methods as well as disinfection methods for protecting against cryptosporidiosis, which is caused by C. parvum. In this study, we investigated the ability of pulsed-light irradiation at 200-900 nm to inactivate C. parvum. Absolute quantitative real-time PCR was performed with cDNA made from total RNA extracted from C. parvum oocysts or HCT-8 cells infected with C. parvum oocysts in vitro. C. parvum oocysts in 100-mL quartz flasks were positioned 20, 30, and 40 cm from the light source, and the duration of irradiation was either 5 or 60 s. The reductions in oocyst viability (4.9 log10) and infectivity (6 log10) were maximal when the C. parvum oocysts were irradiated 20 cm from the pulsed-light source for 60 s, for which the UV dose was 278 mJ/cm2. The minimum dose of pulsed-UV light required for effective reduction in C. parvum infectivity (2 log10) was 15 mJ/cm2, which was achieved by 5 s of irradiation at 30 cm from the light source. This study confirmed that short-duration pulsed-UV light is an effective disinfection measure for C. parvum.

Effects of ozone and ultraviolet radiation treatments on the infectivity of Toxoplasma gondii oocysts

Clinical toxoplasmosis in humans has been epidemiologically linked to the consumption of drinking water contaminated by Toxoplasma gondii oocysts. We evaluated killing of T. gondii oocysts after ultraviolet (UV) or ozone treatments by bioassay in mice and/or cell culture. A 4-log inactivation of the oocyst/sporozoite infectivity was obtained for UV fluences >20 mJ cm(-2). In contrast, oocysts were not inactivated by ozone with an exposure (Ct) up to 9.4 mg min l (-1) in water at 20 degrees C. In conclusion, UV treatment can be an effective disinfection method to inactivate T. gondii oocysts in drinking water, but ozone did not show promise in this research.

Artificial UV-B and solar radiation reduce in vitro infectivity of the human pathogen Cryptosporidium parvum

The potential for solar ultraviolet (UV) radiation to act as a significant abiotic control of Cryptosporidium parvum oocysts in nature is unknown. Infectivity of C. parvum following exposure to artificial UV-B and natural solar radiation, with and without UV wavelengths, was tested under controlled pH and temperature conditions. Percent infectivity of exposed oocysts was determined by in vitro cell culture. Artificial UV-B exposures of 32 and 66 kJ/m2 significantly decreased oocyst infectivity by an average of 58 and 98%, respectively. Exposure of oocysts to approximately half and full intensity of full solar spectrum (all wavelengths) for a period of less than 1 day (10 h) in mid-summer reduced mean infectivity by an average of 67% and >99.99%, respectively. Exposure of the C. parvum oocysts to UV-shielded solar radiation (>404 nm) in early autumn reduced mean infectivity by 52%, while full spectrum solar radiation (exposure at all wavelengths) reduced mean infectivity by 97%. The data provide strong evidence that exposure to natural solar radiation can significantly reduce C. parvum infectivity. Direct effects of solar radiation on oocysts in nature will depend on the depth distribution of the oocysts, water transparency, mixing conditions, and perhaps other environmental factors such as temperature, pH, and stress.

Disinfection of drinking water contaminated with Cryptosporidium parvum oocysts under natural sunlight and using the photocatalyst TiO2

The results of a batch-process solar disinfection (SODIS) and solar photocatalytic disinfection (SPCDIS) on drinking water contaminated with Cryptosporidium are reported. Cryptosporidium parvum oocyst suspensions were exposed to natural sunlight in Southern Spain and the oocyst viability was evaluated using two vital dyes [4',6-diamidino-2-phenylindole (DAPI) and propidium iodide (PI)]. SODIS exposures (strong sunlight) of 8 and 12h reduced oocyst viability from 98% (+/-1.3%) to 11.7% (+/-0.9%) and 0.3% (+/-0.33%), respectively. SODIS reactors fitted with flexible plastic inserts coated with TiO2 powder (SPCDIS) were found to be more effective than those which were not. After 8 and 16 h of overcast and cloudy solar irradiance conditions, SPCDIS reduced oocyst viability from 98.3% (+/-0.3%) to 37.7% (+/-2.6%) and 11.7% (+/-0.7%), respectively, versus to that achieved using SODIS of 81.3% (+/-1.6%) and 36.0% (+/-1.0%), respectively. These results confirm that solar disinfection of drinking water can be an effective household intervention against Cryptosporidium contamination.

Physical inactivation of Toxoplasma gondii oocysts in water

Inactivation of Toxoplasma gondii oocysts occurred with exposure to pulsed and continuous UV radiation, as evidenced by mouse bioassay. Even at doses of >or=500 mJ/cm2, some oocysts retained their viability.

Effectiveness of standard UV depuration at inactivating Cryptosporidium parvum recovered from spiked Pacific oysters (Crassostrea gigas)

When filter-feeding shellfish are consumed raw, because of their ability to concentrate and store waterborne pathogens, they are being increasingly associated with human gastroenteritis and have become recognized as important pathogen vectors. In the shellfish industry, UV depuration procedures are mandatory to reduce pathogen levels prior to human consumption. However, these guidelines are based around more susceptible fecal coliforms and Salmonella spp. and do not consider Cryptosporidium spp., which have significant resistance to environmental stresses. Thus, there is an urgent need to evaluate the efficiency of standard UV depuration against the survival of Cryptosporidium recovered from shellfish. Our study found that in industrial-scale shellfish depuration treatment tanks, standard UV treatment resulted in a 13-fold inactivation of recovered, viable C. parvum oocysts from spiked (1 x 10(6) oocysts liter (-1)) Pacific oysters. Depuration at half power also significantly reduced (P < 0.05; ninefold) the number of viable oocysts recovered from oysters. While UV treatment resulted in significant reductions of recovered viable oocysts, low numbers of viable oocysts were still recovered from oysters after depuration, making their consumption when raw a public health risk. Our study highlights the need for increased periodic monitoring programs for shellfish harvesting sites, improved depuration procedures, and revised microbial quality control parameters, including Cryptosporidium assessment, to minimize the risk of cryptosporidiosis.

Batch solar disinfection inactivates oocysts of Cryptosporidium parvum and cysts of Giardia muris in drinking water

AIM

To determine whether batch solar disinfection (SODIS) can be used to inactivate oocysts of Cryptosporidium parvum and cysts of Giardia muris in experimentally contaminated water.

METHODS AND RESULTS

Suspensions of oocysts and cysts were exposed to simulated global solar irradiation of 830 W m(-2) for different exposure times at a constant temperature of 40 degrees C. Infectivity tests were carried out using CD-1 suckling mice in the Cryptosporidium experiments and newly weaned CD-1 mice in the Giardia experiments. Exposure times of > or =10 h (total optical dose c. 30 kJ) rendered C. parvum oocysts noninfective. Giardia muris cysts were rendered completely noninfective within 4 h (total optical dose >12 kJ). Scanning electron microscopy and viability (4',6-diamidino-2-phenylindole/propidium iodide fluorogenic dyes and excystation) studies on oocysts of C. parvum suggest that inactivation is caused by damage to the oocyst wall.

CONCLUSIONS

Results show that cysts of G. muris and oocysts of C. parvum are rendered completely noninfective after batch SODIS exposures of 4 and 10 h (respectively) and is also likely to be effective against waterborne cysts of Giardia lamblia.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results demonstrate that SODIS is an appropriate household water treatment technology for use as an emergency intervention in aftermath of natural or man-made disasters against not only bacterial but also protozoan pathogens.

Detection of UV-induced thymine dimers in individual Cryptosporidium parvum and Cryptosporidium hominis oocysts by immunofluorescence microscopy

To investigate the effect of UV light on Cryptosporidium parvum and Cryptosporidium hominis oocysts in vitro, we exposed intact oocysts to 4-, 10-, 20-, and 40-mJ x cm-2 doses of UV irradiation. Thymine dimers were detected by immunofluorescence microscopy using a monoclonal antibody against cyclobutyl thymine dimers (anti-TDmAb). Dimer-specific fluorescence within sporozoite nuclei was confirmed by colocalization with the nuclear fluorogen 4',6'-diamidino-2-phenylindole (DAPI). Oocyst walls were visualized using either commercial fluorescein isothiocyanate-labeled anti-Cryptosporidium oocyst antibodies (FITC-CmAb) or Texas Red-labeled anti-Cryptosporidium oocyst antibodies (TR-CmAb). The use of FITC-CmAb interfered with TD detection at doses below 40 mJ x cm-2. With the combination of anti-TDmAb, TR-CmAb, and DAPI, dimer-specific fluorescence was detected in sporozoite nuclei within oocysts exposed to 10 to 40 mJ x cm-2 of UV light. Similar results were obtained with C. hominis. C. parvum oocysts exposed to 10 to 40 mJ x cm-2 of UV light failed to infect neonatal mice, confirming that results of our anti-TD immunofluorescence assay paralleled the outcomes of our neonatal mouse infectivity assay. These results suggest that our immunofluorescence assay is suitable for detecting DNA damage in C. parvum and C. hominis oocysts induced following exposure to UV light.

Cryptosporidium parvum sporozoites contain glutathione

We used the fluorescent dye monochlorobimane (MCB) which binds glutathione (GSH) to localize between 2 and 6 distinctly labelled nuclear and cytoplasmic GSH foci in recently excreted and aged, intact Cryptosporidium parvum oocysts and sporozoites. Buthionine sulfoximine (BSO), a potent and specific inhibitor of GSH, was used to determine whether GSH is synthesized in BSO-treated C. parvum oocysts, by labelling treated oocysts with MCB. Both visual and electronic quantifications were performed. At 5 mM BSO, a significant inhibition of MCB fluorescence, reflecting reduced MCB uptake, was observed in GSH-depleted oocysts (mean +/- S.D. 35 +/- 3.7) compared with controls (3.3 +/- 1.2, P = 0). This clear reduction occurred only in viable oocysts. 1 mM BSO-treated oocysts exhibited weak or no MCB fluorescence, although they were viable (excluded propidium iodide, PI)), and intact and contained sporozoites by differential interference contrast microscopy (DIC). MCB was used in conjunction with PI to determine C. parvum oocyst viability. Oocysts labelled with MCB/PI or 4'6-diamidino-2-phenyl indole (DAPI)/PI produced comparable labelling patterns. Viable oocysts were labelled with MCB or DAPI whereas dead oocysts were labelled with PI only. The localization of GSH in viable, intact oocysts and excysted sporozoites and UV light-irradiated oocysts and sporozoites revealed no changes in MCB uptake at levels up to 40 mJ.cm(-2) irradiation. Although GSH can be detected following MCB localization in both the nucleus and cytoplasm of sporozoites, and can be specifically depleted by BSO treatment, MCB is unlikely to be useful as a surrogate for detecting UV damage in UV-treated Cryptosporidium oocysts.

Evaluation of activated sludge treatment and the efficiency of the disinfection of Giardia species cysts and Cryptosporidium oocysts by UV at a sludge treatment plant in Campinas, south-east Brazil

Among many waterborne diseases the giardiasis and cryptosporidiosis are of particular public health interest, because Giardia cysts and Cryptosporidium oocysts can persist for long periods in the environment, and both pathogenic protozoa have been implicated as the cause of many outbreaks of gastroenteritis in the last 25 years. In order to evaluate the efficiency of cysts and oocysts' removal by the activated sludge process, and by UV reactor in inactivating cysts and oocysts in one wastewater treatment plant (WWTP) of Campinas, three sampling points were selected for study: (1) influent, (2) treated effluent without UV disinfection and (3) treated effluent with UV disinfection. Giardia spp. cysts prevailed with higher density in the three different sample types. Cryptosporidium spp. oocysts were observed in only two samples of influent and just one sample of treated sewage with UV disinfection. In the animal infectivity assay for Giardia spp, one mouse of the UV treated group revealed trophozoites in intestinal scrapings. The results of the present study indicate that treatment by activated sludge process delivered a reduction of 98.9% of cysts and 99.7% of oocysts and UV disinfection was not completely efficient regarding the inactivation of Giardia cysts in the case of the WWTP studied.

The Effects of E-beam Irradiation and Microwave Energy on Eastern Oysters (Crassostrea virginica) Experimentally Infected withCryptosporidium parvum

Shellfish have been identified as a potential source of Cryptosporidium infection for humans. The inactivation of C. parvum and other pathogens in raw molluscan shellfish would provide increased food safety for normal and at-risk consumers. The present study examined the efficacy of two alternative food-processing treatments, e-beam irradiation and microwave energy, on the viability of C. parvum oocysts in Eastern Oysters (Crassostrea virginica), which were artificially infected with the Beltsville strain of C. parvum. The effects of the treatments were evaluated by oral feeding of the processed oyster tissues to neonatal mice. Significant reductions (P<0.05) in infectivity were observed for in-shell and shucked oysters treated with e-beam irradiation at doses of 1.0, 1.5, or 2 kGy vs. untreated controls. A dose of 2 kGy completely eliminated C. parvum infectivity and did not adversely affect the visual appearance of the oysters. Oyster tissue treated with microwave exposures of 1 s (43.2 degrees C), 2 s (54.0 degrees C), and 3 s (62.5 degrees C) showed a reduction in C. parvum mouse infectivity, but the effects were not significantly different (P>0.05) from controls. Microwave energy treatments at 2 and 3 s showed extensive changes in oyster meat texture and color. Thus, because of lack of efficacy and unacceptable tissue changes, microwave treatment of oysters is not considered a viable food-processing method.

Effect of lot variability on ultraviolet radiation inactivation kinetics of Cryptosporidium parvum oocysts

Numerous studies have demonstrated the efficiency of ultraviolet (UV) radiation for the inactivation of oocysts of Cryptosporidium parvum. In these studies inactivation is measured as reduction in oocysts. A primary goal is to estimate the UV radiation required to achieve a high degree of inactivation. Different lots of Cryptosporidium parvum oocysts are used in these studies, and the inactivation rate may vary depending on the lot of oocysts used. The goal of this paper is to account for the error in estimating the amount of inactivation after exposure to UV radiation, and for the effect of lot variability in determining the required UV radiation. A Bayesian approach is used to simultaneously model the logistic dose-response model and the UV inactivation kinetic model. The oocysts lot variability is incorporated using a hierarchical Bayesian model. Posterior distributions using Markov Chain Monte Carlo method is used to obtain estimates and Bayesian credible interval for the required UV radiation to achieve a given inactivation level of Cryptosporidium parvum oocysts.

Effect of batch-process solar disinfection on survival of Cryptosporidium parvum oocysts in drinking water

The results of batch-process solar disinfection (SODIS) of Cryptosporidium parvum oocysts in water are reported. Oocyst suspensions were exposed to simulated sunlight (830 W m(-2)) at 40 degrees C. Viability assays (4',6'-diamidino-2-phenylindole [DAPI]/propidium iodide and excystation) and infectivity tests (Swiss CD-1 suckling mice) were performed. SODIS exposures of 6 and 12 h reduced oocyst infectivity from 100% to 7.5% (standard deviation = 2.3) and 0% (standard deviation = 0.0), respectively.

UV inactivation of Cryptosporidium hominis as measured in cell culture

The Cryptosporidium spp. UV disinfection studies conducted to date have used Cryptosporidium parvum oocysts. However, Cryptosporidium hominis predominates in human cryptosporidiosis infections, so there is a critical need to assess the efficacy of UV disinfection of C. hominis. This study utilized cell culture-based methods to demonstrate that C. hominis oocysts displayed similar levels of infectivity and had the same sensitivity to UV light as C. parvum. Therefore, the water industry can be confident about extrapolating C. parvum UV disinfection data to C. hominis oocysts.

Protection of calves against cryptosporiosis by oral inoculation with gamma-irradiated Cryptosporidium parvum oocysts

The purpose of this study was to determine whether gamma-irradiated Cryptosporidium parvum oocysts could elicit protective immunity against cryptosporidiosis in dairy calves. Cryptosporidium parvum Iowa strain oocysts (1 x 10(6) per inoculation) were exposed to various levels of gamma irradiation (350-500 Gy) and inoculated into 1-day-old dairy calves. The calves were examined daily for clinical signs of cryptosporidiosis, and fecal samples were processed for the presence of C. parvum oocysts. At 21 days of age, the calves were challenged by oral inoculation with 1 x 10(5) C. parvum oocysts and examined daily for oocyst shedding and clinical cryptosporidiosis. Calves that were inoculated with C. parvum oocysts exposed to 350-375 Gy shed C. parvum oocysts in feces. Higher irradiation doses (450 or 500 Gy) prevented oocyst development, but the calves remained susceptible to C. parvum challenge infection. Cryptosporidium parvum oocysts exposed to 400 Gy were incapable of any measurable development but retained the capacity to elicit a protective response against C. parvum challenge. These findings indicate that it may be possible to protect calves against cryptosporidiosis by inoculation with C. parvum oocysts exposed to 400-Gy gamma irradiation.

Efficacy of UV irradiation in inactivating Cryptosporidium parvum oocysts

To evaluate the effectiveness of UV irradiation in inactivating Cryptosporidium parvum oocysts, the animal infectivities and excystation abilities of oocysts that had been exposed to various UV doses were determined. Infectivity decreased exponentially as the UV dose increased, and the required dose for a 2-log(10) reduction in infectivity (99% inactivation) was approximately 1.0 mWs/cm(2) at 20 degrees C. However, C. parvum oocysts exhibited high resistance to UV irradiation, requiring an extremely high dose of 230 mWs/cm(2) for a 2-log(10) reduction in excystation, which was used to assess viability. Moreover, the excystation ability exhibited only slight decreases at UV doses below 100 mWs/cm(2). Thus, UV treatment resulted in oocysts that were able to excyst but not infect. The effects of temperature and UV intensity on the UV dose requirement were also studied. The results showed that for every 10 degrees C reduction in water temperature, the increase in the UV irradiation dose required for a 2-log(10) reduction in infectivity was only 7%, and for every 10-fold increase in intensity, the dose increase was only 8%. In addition, the potential of oocysts to recover infectivity and to repair UV-induced injury (pyrimidine dimers) in DNA by photoreactivation and dark repair was investigated. There was no recovery in infectivity following treatment by fluorescent-light irradiation or storage in darkness. In contrast, UV-induced pyrimidine dimers in the DNA were apparently repaired by both photoreactivation and dark repair, as determined by endonuclease-sensitive site assay. However, the recovery rate was different in each process. Given these results, the effects of UV irradiation on C. parvum oocysts as determined by animal infectivity can conclusively be considered irreversible.

Characterisation of the cysteine protease ER60 in transgenic Schistosoma mansoni larvae

Proteinases have been found to play important roles in parasites. They are involved in developmental processes and facilitate invasion of host tissues as well as the digestion of host molecules for nutrition. The cysteine protease ER60 from Schistosoma mansoni, originally characterised in adults to be expressed in excretory organs, was analysed in larval stages. Transcripts were found in miracidia, in vitro generated mother sporocysts and cercariae. After cloning the promoter and terminator of the ER60 gene, a transformation vector was constructed containing the green fluorescent protein reporter gene flanked by the regulatory elements. The ER60-green fluorescent protein vector was used for transfection experiments of COS-7 cells demonstrating the functionality of the promoter in the heterologous system. To analyse the expression pattern of ER60-green fluorescent protein in larval S. mansoni, in vitro generated mother sporocysts were transformed by particle bombardment, a method which allows gene transfer into schistosomes. Molecular analyses demonstrated transcription and translation of the transgene. Furthermore, confocal laser scanning microscopy revealed ER60-induced green fluorescent protein fluorescence within the larvae. Inside primary sporocysts, tissue-specific activity was localised in the gland cells, protonephridia and several cytons. These results suggest that ER60 is expressed in the ES system of larvae and, amongst other functions, may play a role in penetration and migration processes.