Norwalk virus and other human caliciviruses (noroviruses) are major agents of gastroenteritis, and water is a major route of their transmission. In an effort to control Norwalk virus in drinking water, Norwalk virus reduction by bench-scale ozone disinfection was determined using quantitative reverse transcription (RT)-PCR for virus assays. Two other enteric viruses, poliovirus 1 and coliphage MS2, were included for comparison, and their reductions were assayed by infectivity assays as well as by RT-PCR. Virus reductions by ozone were determined using a dose of 0.37 mg of ozone/liter at pH 7 and 5°C for up to 5 min. Based on two RT-PCR assays, the reductions of Norwalk virus were >3 log 10 within a contact time of 10 s, and these were similar to the reductions of the other two viruses determined by the same assay methods. Also, the virus reductions detected by RT-PCR assays were similar to those detected by infectivity assays, indicating that the RT-PCR assay is a reliable surrogate assay for both culturable and nonculturable viruses disinfected with ozone. Overall, the results of this study indicate that Norwalk virus as well as other enteric viruses can be reduced rapidly and extensively by ozone disinfection and that RT-PCR is a useful surrogate assay for both culturable and nonculturable viruses disinfected with ozone.Norwalk virus (NV) and other human caliciviruses (noroviruses) are major agents of epidemic gastroenteritis, and water is an important route of their transmission (5). These viruses are also suspected to be important agents of endemic gastroenteritis caused by fecally contaminated drinking water (8). Furthermore, a previous study suggested that NV is very resistant to free-chlorine disinfection (6) because a virus suspension in water was still infectious after administration of a dose of 3.75 mg of free chlorine/liter and a contact time of 30 min. Poliovirus and rotaviruses were completely inactivated at the same disinfection condition. Considering the apparent high infectivity (low infectious dose) and widespread occurrence in the population, the resistance of NV to chlorination could pose a high risk to the public who are served by conventionally treated, chlorinated drinking water.Because NV cannot be grown or assayed for infectivity in any known laboratory host (5), reverse transcription (RT)-PCR is the only sensitive and specific assay system currently available. However, it was not certain whether the RT-PCR assay could accurately predict the loss of virus infectivity by disinfection. Therefore, two other enteric viruses, poliovirus 1 (PV1) and coliphage MS2, were included in this study to allow comparison of RT-PCR assay data with infectivity assay data for these viruses and thereby determine whether the assays provide equivalent information. Also, these two viruses have been widely used as indicator viruses for disinfection efficiency (13). A previous study reported that RT-PCR, especially RT-PCR for small (Ͻ300 nucleotides) targets, may not reliably quantify virus infectivity because t...

We demonstrate highly sensitive detection of viruses using terahertz split-ring resonators with various capacitive gap widths. Two types of viruses, with sizes ranging from 60 nm (PRD1) to 30 nm (MS2), were detected at low densities on the metamaterial surface. The dielectric constants of the virus layers in the THz frequency range were first measured using thick films, and the large values found identified them as efficient target substances for dielectric sensing. We observed the resonance-frequency shift of the THz metamaterial following deposition of the viruses on the surface at low-density. The resonance shift was higher for the MS2 virus, which has a relatively large dielectric constant. The frequency shift increases with surface density until saturation and the sensitivity is then obtained from the initial slope. Significantly, the sensitivity increases by about 13 times as the gap width in the metamaterials is decreased from 3 µm to 200 nm. This results from a combination of size-related factors, leading to field enhancement accompanying strong field localization.

The human and animal pathogen Giardia lamblia is a waterborne risk to public health because the cysts are ubiquitous and persistent in water and wastewater, not completely removed by physical-chemical treatment processes, and relatively resistant to chemical disinfection. Given the recently recognized efficacy of UV irradiation against Cryptosporidium parvum oocysts, the inactivation of G. lamblia cysts in buffered saline water at pH 7.3 and room temperature by near monochromatic (254 nm) UV irradiation from low-pressure mercury vapor lamps was determined using a "collimated beam" exposure system. Reduction of G. lamblia infectivity for gerbils was very rapid and extensive, reaching a detection limit of >4 log within a dose of 10 JM-2. The ability of UV-irradiated G. lamblia cysts to repair UV-induced damage following typical drinking water and wastewater doses of 160 and 400 JM(-2) was also investigated using experimental protocols typical for bacterial and eucaryotic DNA repair under both light and dark conditions. The infectivity reduction of G. lamblia cysts at these UV doses remained unchanged after exposure to repair conditions. Therefore, no phenotypic evidence of either light or dark repair of DNA damage caused by LP UV irradiation of cysts was observed at the UV doses tested. We conclude that UV disinfection at practical doses achieves appreciable (much greater than 4 log) inactivation of G. lamblia cysts in water with no evidence of DNA repair leading to infectivity reactivation.

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Because Cryptosporidium parvum oocysts are very resistant to conventional water treatment processes, including chemical disinfection, we determined the kinetics and extent of their inactivation by monochromatic, low-pressure (LP), mercury vapor lamp UV radiation and their subsequent potential for DNA repair of UV damage. A UV collimated-beam apparatus was used to expose suspensions of purified C. parvum oocysts in phosphate-buffered saline, pH 7.3, at 25°C to various doses of monochromatic LP UV. C. parvum infectivity reductions were rapid, approximately first order, and at a dose of 3 mJ/cm 2 ‫03؍(‬ J/m 2 ), the reduction reached the cell culture assay detection limit of ϳ3 log 10 . At UV doses of 1.2 and 3 mJ/cm 2 , the log 10 reductions of C. parvum oocyst infectivity were not significantly different for control oocysts and those exposed to dark or light repair conditions for UV-induced DNA damage. These results indicate that C. parvum oocysts are very sensitive to inactivation by low doses of monochromatic LP UV radiation and that there is no phenotypic evidence of either light or dark repair of UV-induced DNA damage.Cryptosporidium parvum is an important health-related waterborne pathogen that is ubiquitous in surface and source waters (16) and very resistant to conventional water treatment processes (9). Although conventional water filtration systems achieve some removal (9), chemical disinfection by chlorination is incapable of achieving appreciable inactivation of C. parvum oocysts at practical disinfectant doses and contact times (7,23). Previous studies using the in vitro viability assays of excystation and vital dye staining suggested that C. parvum oocysts are also very resistant to monochromatic low-pressure (LP) UV radiation (5, 21) and much more resistant than the enteric viruses that have been proposed as the basis for determining UV dosimetry in water and wastewater treatment (11,12,19). However, recent studies using in vivo animal bioassays indicate that polychromatic medium-pressure mercury lamp UV as well as LP UV extensively reduce C. parvum oocyst infectivity at relatively low doses (4, 6).Animal bioassays are considered the "gold standard" for assessing Cryptosporidium oocyst infectivity (14). However, they are costly, require tedious and lengthy procedures for handling animals and scoring for infection, give variable and imprecise estimates of infectious dose and infectivity concentrations, and raise ethical concerns about the use of experimental animals when alternative infectivity assays are available (24). In vitro cell culture infectivity assays using fluorescent antibodies against living stages of C. parvum (27, 32) are reliable and convenient alternatives to animal infectivity assays, but comparisons of cell culture and animal infectivity assays for assessing UV inactivation of Cryptosporidium oocysts have not yet been reported in the literature. In this study, we compared mouse and cell culture infectivity assays in LP UV disinfection experiments on C. parvum oocysts. The kinetics ...

Nucleic acid (NA) amplification techniques are useful to detect viruses in water and other environmental samples because they are highly sensitive, specific and can detect fastidious enteric viruses that do not grow well or not at all in cell cultures. However, RT-PCR was found to detect inactivated viruses. In terms of risks to public health this constitutes a false positive result, as inactivated viruses are no longer infectious. When poliovirus type 1 and coliphage MS2 were studied for (a) persistence in water and sewage and (b) inactivation in water by free chlorine, chlorine dioxide and UV radiation, RT-PCR assays underestimated virus inactivation. The use of multiple RT-PCR amplification sites, larger RT-PCR genomic targets and immunocapture RT-PCR sometimes reduced, but did not eliminate, the discrepancy between loss of infectivity and loss of RT-PCR titre. Virus presence based on RT-PCR detection must be interpreted with caution when predicting human health risks.

To elucidate the roles of physical and chemical properties of viruses and their sensitivity to UV radiation, the kinetics and extent of inactivation of several waterborne pathogenic viruses and bacteriophages with different virion sizes and genomic composition by monochromatic, low-pressure (LP) UV was determined in phosphate buffered saline or a filtered drinking water. The inactivation rates of the small RNA viruses, poliovirus 1 and Coxsackievirus B4, by LP UV were very rapid and reached ~4 log10 and >5 log10, respectively, within a UV dose of 30 mJ/cm2. In contrast, the inactivation of the small RNA bacteriophage, MS2, was much slower and only 2 log10 inactivation was achieved at a UV dose of 30 mJ/cm2. The inactivation of the large DNA virus, adenovirus 2, was relatively slow and only 2 log10 inactivation was achieved with a UV dose of 60 mJ/cm2. In contrast, the inactivation rates of the three large DNA bacteriophages were very rapid and reached >5 log10 with a UV dose of 10 mJ/cm2. Therefore, the results of this study indicate that inactivation of human enteric viruses and bacteriophages by UV irradiation is not simply predictable by the type and size of the virus or its nucleic acid genome and there is no strong correlation between virion size and genetic composition of enteric viruses and their response to LP UV irradiation. Key words: low pressure ultraviolet (LP UV), poliovirus 1, Coxsackievirus B4, bacteriophage MS2, bacteriophage PRD1, adenovirus 2, UV disinfection.

The reduction of Norwalk virus (NV) by a 2 mg/L dose of pre-formed monochloramine was determined at pH 8 and 5°C in bench-scale, batch disinfection experiments using quantitative RT-PCR for NV assays. Two other enteric viruses, poliovirus 1 (PV1) and coliphage MS2, were included for comparison and assayed by infectivity as well as RT-PCR. After 3h, reductions of PV1 and MS2 by infectivity assays were about 1 log10 but there were no reductions of these viruses by RT-PCR assays. Hence, RT-PCR underestimated virus inactivation by monochloramine. However, NV reduction by monochloramine was about 1 log10 by RT-PCR assay, suggesting that it is more susceptible to monochloramine than the other two viruses tested. Based on RT-PCR titre reduction, the CT99 value for NV was about 775 mg-min/L. If the reduction of NV infectivity by monochloramine is ever greater than the reduction of RT-PCR signals, the CT99 value would be smaller. However, the results of this study indicate that NV and the other enteric viruses tested are not rapidly and extensively reduced by disinfection with pre-formed monochloramine.