Virus inactivation mechanisms: impact of disinfectants on virus function and structural integrity

Nano-Sized Copper (Oxide) on Alumina Granules for Water Filtration: Effect of Copper Oxidation State on Virus Removal Performance

Virus removal can be successfully achieved based on an electrostatic adsorption mechanism. The key requirement for this process is to develop filter materials that can be produced by low-cost technologies and are suitable in large-scale production for real applications. In this study, we report development of spray-dried alumina granules modified with copper (oxide) nanoparticles and critically assess the effect of copper oxidation state on virus removal capacity. Using plate-shaped alumina as a support material resulted in porous structure, which in turn ensured prolonged contact time of contaminated water with the material. Subsequently, copper (oxide) nanoparticles provided a large number of adsorption sites. Flow experiments revealed that copper(I) oxide and metallic copper were the active phases in virus removal and 99.9% of MS2 bacteriophages could be removed. However, almost no virus removal was observed in the presence of copper(II) oxide. Contrasting virus removal characteristics are associated with the different surface charge of copper species, as determined by zeta potential measurements.

Humidity-Dependent Decay of Viruses, but Not Bacteria, in Aerosols and Droplets Follows Disinfection Kinetics

The transmission of some infectious diseases requires that pathogens can survive (i.e., remain infectious) in the environment, outside the host. Relative humidity (RH) is known to affect the survival of some microorganisms in the environment; however, the mechanism underlying the relationship has not been explained, particularly for viruses. We investigated the effects of RH on the viability of bacteria and viruses in both suspended aerosols and stationary droplets using traditional culture-based approaches. Results showed that viability of bacteria generally decreased with decreasing RH. Viruses survived well at RHs lower than 33% and at 100%, whereas their viability was reduced at intermediate RHs. We then explored the evaporation rate of droplets consisting of culture media and the resulting changes in solute concentrations over time; as water evaporates from the droplets, solutes such as sodium chloride in the media become more concentrated. Based on the results, we suggest that inactivation of bacteria is influenced by osmotic pressure resulting from elevated concentrations of salts as droplets evaporate. We propose that the inactivation of viruses is governed by the cumulative dose of solutes or the product of concentration and time, as in disinfection kinetics. These findings emphasize that evaporation kinetics play a role in modulating the survival of microorganisms in droplets.

Systematic Review and Meta-Analysis of the Persistence and Disinfection of Human Coronaviruses and Their Viral Surrogates in Water and Wastewater

A systematic review and meta-analysis was conducted to identify decay rate constants (k) of human coronaviruses and their viral surrogates (i.e., animal coronaviruses and the enveloped bacteriophage Phi6) in water and wastewater and disinfection rates with exposure to free chlorine and germicidal ultraviolet light (UV254). Here, 73 k were identified, with only 12 for human coronaviruses, as opposed to animal coronaviruses or Phi6. In the absence of disinfectants, k increased with temperature. Between 22 and 25 °C, mean k for coronaviruses ranged from 0.19 ± 0.06 d-1 in laboratory buffer (n = 4) to 2.9 ± 0.03 d-1 in sterilized wastewater (n = 3), which are within the ranges observed for Phi6 and nonenveloped viruses. No free chlorine or UV254 disinfection studies for coronaviruses were identified that met the systematic review inclusion criteria, although evidence from the literature suggests that coronaviruses would be inactivated if disinfectant doses recommended for nonenveloped viruses were applied. Three disinfection experiments were identified for Phi6. However, given different genome compositions and virion structures between coronaviruses and Phi6, it is not clear whether Phi6 should be used as a surrogate for evaluating free chlorine or UV254k. Therefore, there is a critical need for additional studies that specifically evaluate disinfection kinetics of coronaviruses in the aqueous environment.

Virus inactivation in groundwater in a postglacial lava field in arctic climate

Outbreaks of viral gastroenteritis are often connected to contaminated drinking water. The assessment of the water quality relies on the cultivation of indicator bacteria, and little is known of the fate of viruses in groundwater, especially in arctic regions. In Iceland, the groundwater temperature is between 3 and 6°C. The aim of this study was to determine virus inactivation at low temperature in a groundwater microcosm and in a borehole in a postglacial lava field. Two phage species that are commonly used as surrogates for norovirus were used, MS2 and PhiX174. Dialysis bags were used for the samples, and a device was constructed to hold many samples at a time and protect the samples in the borehole. No significant decrease of infective PhiX174 phages in the borehole or of the MS2 phages in the microcosm was observed. A slightly significant decrease of PhiX174 in the microcosm was noticed, with one log reduction time of 476 days. On the other hand, a significant reduction in MS2 was found in the field test, where the time needed for 90% reduction was 12·5 days. The results showed that an infective virus can exist in groundwater for months or years in arctic regions and a great difference may exist between results from microcosm and field tests. SIGNIFICANCE AND IMPACT OF THE STUDY: This study reveals that arctic regions are highly sensitive to virus contamination as an infective virus may exist in groundwater for years at low temperature. The results also show that the virus inactivation observed in field tests may differ considerably from the inactivation observed in laboratory microcosms. The results emphasize the importance of large protection zones around drinking water intakes as well as good wastewater treatment so that the likelihood of faecal contamination of groundwater is reduced.

Effect of natural ageing and heat treatments on GII.4 norovirus binding to Histo-Blood Group Antigens

Human noroviruses (HuNoVs) are the leading cause of viral foodborne outbreaks worldwide. To date, no available methods can be routinely used to detect infectious HuNoVs in foodstuffs. HuNoVs recognize Histo-Blood Group Antigens (HBGAs) through the binding pocket (BP) of capsid protein VP1, which promotes infection in the host cell. In this context, the suitability of human HBGA-binding assays to evaluate the BP integrity of HuNoVs was studied on GII.4 virus-like particles (VLPs) and GII.4 HuNoVs during natural ageing at 20 °C and heat treatments. Our results demonstrate that this approach may reduce the over-estimation of potential infectious HuNoVs resulting from solely using the genome detection, even though some limitations have been identified. The specificity of HBGA-binding to the BP is clearly dependent on the HGBA type (as previously evidenced) and the ionic strength of the media without disturbing such interactions. This study also provides new arguments regarding the ability of VLPs to mimic HuNoV behavior during inactivation treatments. The BP stability of VLPs was at least 4.3 fold lower than that of HuNoVs at 20 °C, whereas capsids of both particles were disrupted at 72 °C. Thus, VLPs are relevant surrogates of HuNoVs for inactivation treatments inducing significant changes in the capsid structure.

Adapting Translational Research Methods to Water, Sanitation, and Hygiene

Translational research applies scientific techniques to achieve practical outcomes, connecting pure research and pure practice. Many translational research types have arisen since the mid-1900s, reflecting the need to better integrate scientific advancement with policy and practice. Water, sanitation, and hygiene (WaSH) development efforts have aimed to reduce morbidity and mortality and improve service delivery; thus, associated research has a strong orientation toward applied studies that use diverse methods to support decision-making. Drawing from knowledge that emerged to support other professional fields, such as manufacturing and clinical healthcare, we characterize different types of translational research and clarify nomenclature and principles. We describe study approaches relevant to translational research questions, and offer overarching recommendations, specific examples, and resources for further study as practical advice to professionals who seek to apply translational methods to WaSH problems. To enhance collective outcomes, professionals should mindfully align projects within the translational spectrum. We further recommend overarching good practices such as documenting intervention adaptations, overtly considering contextual factors, and better distinguishing efficacy from effectiveness research by replicating studies in different contexts. By consciously improving the compatibility and linkages between WaSH science and practice, this guide can accelerate urgently needed progress toward global development goals.

Hampering Herpesviruses HHV-1 and HHV-2 Infection by Extract of Ginkgo biloba (EGb) and Its Phytochemical Constituents

Despite the availability of several anti-herpesviral agents, it should be emphasized that the need for new inhibitors is highly encouraged due to the increasing resistant viral strains as well as complications linked with periods of recurring viral replication and reactivation of latent herpes infection. Extract of Ginkgo biloba (EGb) is a common phytotherapeutics around the world with health benefits. Limited studies, however, have addressed the potential antiviral activities of EGb, including herpesviruses such as Human alphaherpesvirus 1 (HHV-1) and Human alphaherpesvirus 2 (HHV-2). We evaluated the antiviral activity of EGb and its phytochemical constituents: flavonoids and terpenes against HHV-1 and HHV-2. Pretreatment of the herpesviruses with EGb prior to infection of cells produced a remarkable anti-HHV-1 and anti-HHV-2 activity. The extract affected the viruses before adsorption to cell surface at non-cytotoxic concentrations. In this work, through a comprehensive anti-HHV-1 and anti-HHV-2 activity study, it was revealed that flavonoids, especially isorhamnetin, are responsible for the antiviral activity of EGb. Such activity was absent in quercetin and kaempferol. However, EGb showed the most potent antiviral potency compared to isorhamnetin. EGb could augment current therapies for herpes labialis and genital herpes. Moreover, the potential use of EGb in multidrug therapy with synthetic anti-herpes compounds might be considered.

Free Chlorine Disinfection Mechanisms of Rotaviruses and Human Norovirus Surrogate Tulane Virus Attached to Fresh Produce Surfaces

To fill the knowledge gap on how effective free chlorine is against viral-contaminated produce, we inoculated the surfaces of outdoor- or greenhouse-grown kale and mustard with Rotavirus (RV) or a human norovirus surrogate (Tulane virus, TV) and then disinfected the leaves with free chlorine. Disinfection efficacies for RV strain OSU and Wa were approximately 1-log10 higher when attached to mustard than to kale. Similar disinfection efficacies were observed for TV attached to mustard or kale. When examining TV and RV OSU in suspension (not attached to leaf surfaces), TV was more resistant to free chlorine than RV OSU. Inactivation efficacies were higher for these viruses in suspension versus viruses attached to produce the surface. We also found that free chlorine damaged viral capsids, allowing free chlorine access to viral RNA to damage viral genomes. Exposure to free chlorine at 1.7 ppm over 1 min caused VP8* of RV OSU to lose its ability to bind to its host receptors. TV lost its ability to bind to its receptor only after exposure to free chlorine at 29 ppm over 1 min. Thus, to reduce foodborne viral infections, it is important to consider the differences in virus' reactivity and inactivation mechanisms with free chlorine.

Effects of cavitation on different microorganisms: The current understanding of the mechanisms taking place behind the phenomenon. A review and proposals for further research

A sudden decrease in pressure triggers the formation of vapour and gas bubbles inside a liquid medium (also called cavitation). This leads to many (key) engineering problems: material loss, noise, and vibration of hydraulic machinery. On the other hand, cavitation is a potentially useful phenomenon: the extreme conditions are increasingly used for a wide variety of applications such as surface cleaning, enhanced chemistry, and wastewater treatment (bacteria eradication and virus inactivation). Despite this significant progress, a large gap persists between the understanding of the mechanisms that contribute to the effects of cavitation and its application. Although engineers are already commercializing devices that employ cavitation, we are still not able to answer the fundamental question: What precisely are the mechanisms how bubbles can clean, disinfect, kill bacteria and enhance chemical activity? The present paper is a thorough review of the recent (from 2005 onward) work done in the fields of cavitation-assisted microorganism's destruction and aims to serve as a foundation to build on in the next years.

Assessment of the Applicability of Capsid-Integrity Assays for Detecting Infectious Norovirus Inactivated by Heat or UV Irradiation

Human noroviruses are the leading cause of viral gastroenteritis. In the absence of a practical culture technique for routine analysis of infectious noroviruses, several methods have been developed to discriminate between infectious and non-infectious viruses by removing non-viable viruses prior to analysis by RT-qPCR. In this study, two such methods (RNase and porcine gastric mucin) which were designed to remove viruses with compromised capsids (and therefore assumed to be non-viable), were assessed for their ability to quantify viable F-specific RNA bacteriophage (FRNAP) and human norovirus following inactivation by UV-C or heat. It was found that while both methods could remove a proportion of non-viable viruses, a large proportion of non-viable virus remained to be detected by RT-qPCR, leading to overestimations of the viable population. A model was then developed to determine the proportion of RT-qPCR detectable RNA from non-viable viruses that must be removed by such methods to reduce overestimation to acceptable levels. In most cases, nearly all non-viable virus must be removed to reduce the log overestimation of viability to within levels that might be considered acceptable (e.g. below 0.5 log₁₀). This model could be applied when developing alternative pre-treatment methods to determine how well they should perform to be comparable to established infectivity assays.

Assessing the Occurrence of Waterborne Viruses in Reuse Systems: Analytical Limits and Needs

Detection of waterborne enteric viruses is an essential tool in assessing the risk of waterborne transmission. Cell culture is considered a gold standard for detection of these viruses. However, it is important to recognize the uncertainty and limitations of enteric virus detection in cell culture. Cell culture cannot support replication of all virus types and strains, and numerous factors control the efficacy of specific virus detection assays, including chemical additives, cell culture passage number, and sequential passage of a sample in cell culture. These factors can result in a 2- to 100-fold underestimation of virus infectivity. Molecular methods reduce the time for detection of viruses and are useful for detection of those that do not produce cytopathogenic effects. The usefulness of polymerase chain reaction (PCR) to access virus infectivity has been demonstrated for only a limited number of enteric viruses and is limited by an understanding of the mechanism of virus inactivation. All of these issues are important to consider when assessing waterborne infectious viruses and expected goals on virus reductions needed for recycled water. The use of safety factors to account for this may be useful to ensure that the risks in drinking water and recycled water for potable reuse are minimized.

Differences in Viral Disinfection Mechanisms as Revealed by Quantitative Transfection of Echovirus 11 Genomes

Virus inactivation mechanisms can be elucidated by methods that measure the loss of specific virus functionality (e.g., host attachment, genome internalization, and genome replication). Genome functionality is frequently assessed by PCR-based methods, which are indirect and potentially inaccurate; genome damage that affects detection by high-fidelity PCR enzymes may not adversely affect the ability of actual cellular enzymes to produce functional virus. Therefore, we developed here a transfection-based assay to quantitatively determine viral genome functionality by inserting viral RNA into host cells directly to measure their ability to produce new functional viruses from damaged viral genomes. Echovirus 11 was treated with ozone, free chlorine (FC), UV light at 254 nm (UV₂₅₄), or heat, and then the reductions in genome functionality and infectivity were compared. Ozone reduced genome functionality proportionally to infectivity, indicating that genome damage is the main mechanism of virus inactivation. In contrast, FC caused little or no loss of genome functionality compared to infectivity, indicating a larger role for protein damage. For UV₂₅₄, genome functionality loss accounted for approximately 60% of virus inactivation, with the remainder presumably due to protein damage. Heat treatment resulted in no reduction in genome functionality, in agreement with the understanding that heat inactivation results from capsid damage. Our results indicate that there is a fundamental difference between genome integrity reductions measured by PCR enzymes in previous studies and actual genome functionality (whether the genome can produce virus) after disinfection. Compared to PCR, quantitative transfection assays provide a more realistic picture of actual viral genome functionality and overall inactivation mechanisms during disinfection.IMPORTANCE This study provides a new tool for assessing virus inactivation mechanisms by directly measuring a viral genome's ability to produce new viruses after disinfection. In addition, we identify a potential pitfall of PCR for determining virus genome damage, which does not reflect whether a genome is truly functional. The results presented here using quantitative transfection corroborate previously suggested virus inactivation mechanisms for some virus inactivation methods (heat) while bringing additional insights for others (ozone, FC, and UV₂₅₄). The developed transfection method provides a more mechanistic approach for the assessment of actual virus inactivation by common water disinfectants.

Progress in the study of virus detection methods: The possibility of alternative methods to validate virus inactivation

Virus inactivation validation studies have been widely applied in the risk assessment of biogenic material-based medical products, such as biological products, animal tissue-derived biomaterials, and allogeneic biomaterials, to decrease the risk of virus transmission. Traditional virus detection methods in an inactivation validation study utilize cell culture as a tool to quantify the infectious virus by observing cytopathic effects (CPEs) after virus inactivation. However, this is susceptible to subjective factors because CPEs must be observed by experts under a microscope during virus titration. In addition, this method is costly and time- and labor-consuming. Molecular biological technologies such as quantitative polymerase chain reaction (qPCR) have been widely used for virus detection but cannot distinguish infectious and noninfectious viruses. Therefore, qPCR cannot be directly applied to virus inactivation validation studies. In this paper, methods to detect viruses and progress in the challenge of differentiating infectious and noninfectious viruses with the combination of pretreatment and qPCR techniques such as the integrated cell culture-qPCR (ICC-qPCR) method are reviewed. In addition, the advantages and disadvantages of each new method, as well as its prospect in virus inactivation validation studies, are discussed.

Water Disinfection in Rural Areas Demands Unconventional Solar Technologies

Providing access to safe drinking water is a prerequisite for protecting public health. Vast improvements in drinking water quality have been witnessed during the last century, particularly in urban areas, thanks to the successful implementation of large, centralized water treatment plants and the distribution of treated water via underground networks of pipes. Nevertheless, infection by waterborne pathogens through the consumption of biologically unsafe drinking water remains one of the most significant causes of morbidity and mortality in developing rural areas. In these areas, the construction of centralized water treatment and distribution systems is impractical due to high capital costs and lack of existing infrastructure. Improving drinking water quality in developing rural areas demands a paradigm shift to unconventional, innovative water disinfection strategies that are low cost and simple to implement and maintain, while also requiring minimal infrastructure. The implementation of point-of-use (POU) disinfection techniques at the household- or community-scale is the most promising intervention strategy for producing immediate health benefits in the most vulnerable rural populations. Among POU techniques, solar-driven processes are considered particularly instrumental to this strategy, as developing rural areas that lack safe drinking water typically receive higher than average surface sunlight irradiation. Materials that can efficiently harvest sunlight to produce disinfecting agents are pivotal for surpassing the disinfection performance of conventional POU techniques. In this account, we highlight recent advances in materials and processes that can harness sunlight to disinfect water. We describe the physicochemical properties and molecular disinfection mechanisms for four categories of disinfectants that can be generated by harvesting sunlight: heat, germicidal UV radiation, strong oxidants, and mild oxidants. Our recent work in developing materials-based solar disinfection technologies is discussed in detail, with particular focus on the materials' mechanistic functions and their modes of action for inactivation of three common types of waterborne pathogens (i.e., bacteria, virus, and protozoa). We conclude that different solar disinfection technologies should be applied depending on the source water quality and target pathogen due to significant variations on susceptibility of microbial components to disparate disinfectants. In addition, we expect that ample research opportunities exist on reactor design and process engineering for scale-up and improved performance of these solar materials, while accounting for the infrastructure demand and capital input. Although the practical implementation of new treatment techniques will face social and economic challenges that cannot be overlooked, novel technologies such as these can play a pivotal role in reducing water borne disease burden in rural communities in the developing world.

The impact of chlorine and heat on the infectivity and physicochemical properties of bacteriophage MS2

Enteric viruses and bacteriophages are exposed to various inactivating factors outside their host, and among them chlorine and heat are the most commonly used sanitizer in water industry and treatment in the food industry, respectively. Using MS2 phages as models for enteric viruses, we investigated the impact of free chlorine and heat on their physicochemical properties. Free chlorine was first evaluated alone. No increase in either capsid permeability or hydrophobicity was observed. The negative surface charge slightly increased suggesting molecular changes in the capsid. However, a weakening of the capsid by chlorine was suggested by differential scanning fluorimetry. This phenomenon was confirmed when chlorination was followed by a heat treatment. Indeed, an increase in the inactivation of MS2 phages and the permeability of their capsids to RNases was observed. More interestingly, an increase in the expression of hydrophobic domains at the phage surface was observed, but only for phages remaining infectious. The chlorine-caused weakening of the capsid suggested that, for an optimal use, the oxidant should be followed by heat. The increased permeability to RNases and the expression of hydrophobic domains may contribute to the development or improvement of molecular methods specific for infectious enteric viruses.

Evaluation of Inactivating Norovirus, Hepatitis A, and Listeria monocytogenes on Raspberries by Sanitizer Spray

HIGHLIGHTS

Chlorine and PAA spray reduced MNV and L. monocytogenes from raspberries by <1.0 log. Residual PAA on raspberries further reduced MNV and Listeria during postspray frozen storage. PAA decayed more slowly than active chlorine on raspberry surfaces. The data suggest that PAA could aid in risk reduction of pathogens on raspberries.

Bacterial Stabilization of a Panel of Picornaviruses

Several viruses encounter various bacterial species within the host and in the environment. Despite these close encounters, the effects of bacteria on picornaviruses are not completely understood. Previous work determined that poliovirus (PV), an enteric virus, has enhanced virion stability when exposed to bacteria or bacterial surface polysaccharides such as lipopolysaccharide. Virion stabilization by bacteria may be important for interhost transmission, since a mutant PV with reduced bacterial binding had a fecal-oral transmission defect in mice. Therefore, we investigated whether bacteria broadly enhance stability of picornaviruses from three different genera: Enterovirus (PV and coxsackievirus B3 [CVB3]), Kobuvirus (Aichi virus), and Cardiovirus (mengovirus). Furthermore, to delineate strain-specific effects, we examined two strains of CVB3 and a PV mutant with enhanced thermal stability. We determined that specific bacterial strains enhance thermal stability of PV and CVB3, while mengovirus and Aichi virus are stable at high temperatures in the absence of bacteria. Additionally, we determined that bacteria or lipopolysaccharide can stabilize PV, CVB3, Aichi virus, and mengovirus during exposure to bleach. These effects are likely mediated through direct interactions with bacteria, since viruses bound to bacteria in a pulldown assay. Overall, this work reveals shared and distinct effects of bacteria on a panel of picornaviruses.IMPORTANCE Recent studies have shown that bacteria promote infection and stabilization of poliovirus particles, but the breadth of these effects on other members of the Picornaviridae family is unknown. Here, we compared the effects of bacteria on four distinct members of the Picornaviridae family. We found that bacteria reduced inactivation of all of the viruses during bleach treatment, but not all viral strains were stabilized by bacteria during heat treatment. Overall, our data provide insight into how bacteria play differential roles in picornavirus stability.

Flow cytometry applications in water treatment, distribution, and reuse: A review

Ensuring safe and effective water treatment, distribution, and reuse requires robust methods for characterizing and monitoring waterborne microbes. Methods widely used today can be limited by low sensitivity, high labor and time requirements, susceptibility to interference from inhibitory compounds, and difficulties in distinguishing between viable and non-viable cells. Flow cytometry (FCM) has recently gained attention as an alternative approach that can overcome many of these challenges. This article critically and systematically reviews for the first time recent literature on applications of FCM in water treatment, distribution, and reuse. In the review, we identify and examine nearly 300 studies published from 2000 to 2018 that illustrate the benefits and challenges of using FCM for assessing source-water quality and impacts of treatment-plant discharge on receiving waters, wastewater treatment, drinking water treatment, and drinking water distribution. We then discuss options for combining FCM with other indicators of water quality and address several topics that cut across nearly all applications reviewed. Finally, we identify priority areas in which more work is needed to realize the full potential of this approach. These include optimizing protocols for FCM-based analysis of waterborne viruses, optimizing protocols for specifically detecting target pathogens, automating sample handling and preparation to enable real-time FCM, developing computational tools to assist data analysis, and improving standards for instrumentation, methods, and reporting requirements. We conclude that while more work is needed to realize the full potential of FCM in water treatment, distribution, and reuse, substantial progress has been made over the past two decades. There is now a sufficiently large body of research documenting successful applications of FCM that the approach could reasonably and realistically see widespread adoption as a routine method for water quality assessment.

Effects of pH Variability on Peracetic Acid Reduction of Human Norovirus GI, GII RNA, and Infectivity Plus RNA Reduction of Selected Surrogates

With increasing interest in peracetic acid (PAA) as a disinfectant in water treatment processes, this study determined PAA treatment effects on human noroviruses (hNoVs) genotype I (GI) and genotype II (GII) as well as effects on bacteriophage MS2 and murine norovirus (MNV) in relation to pH. Across all pH conditions, PAA achieved between 0.2 and 2.5 log₁₀ reduction of hNoVs over 120 min contact time in buffer solution as measured by reverse transcription-qPCR (RT-qPCR). The PAA treatments produced similar RT-qPCR reductions of MS2 and MNV, in the range of 0.2-2.7 log₁₀. Infectivity assays achieved > 4 log₁₀ reduction of both MS2 and MNV in buffer solution after 120 min contact time. Comparing PAA activity across varying pH, disinfection at pH 8.5, in general, resulted in less reduction of infectivity and molecular signals compared to pH conditions of 6.5 and 7.5. This difference was most pronounced for reductions in infectivity of MNV and MS2, with as much as 2.7 log₁₀ less reduction at pH 8.5 relative to lower pH conditions. This study revealed that PAA was an effective disinfectant for treatment of hNoV GI and GII, MS2 and MNV, with greatest virus reduction observed for MS2 and MNV infectivity. RT-qPCR reductions of MS2 and MNV were lower than concurrent MS2 and MNV infectivity reductions, suggesting that observed hNoV RT-qPCR reductions may underestimate reductions in hNoV infectivity achieved by PAA. Although virus disinfection by PAA occurred at all evaluated pH levels, PAA is most effective at pH 6.5-7.5.

UV inactivation of human infectious viruses at two full-scale wastewater treatment plants in Canada

Ultraviolet (UV) disinfection is widely used to inactivate microorganisms prior to release of treated municipal wastewater. However, limited data are available for in situ inactivation of infectious enteric viruses by UV treatment at full-scale. In this study, a total of 51 pre-UV and 50 post-UV samples were collected over a two-year period from two wastewater treatment plants (WWTPs) and analyzed for noroviruses, rotavirus, reovirus, sapovirus, astrovirus, enteroviruses, adenoviruses and JC virus. Both pre-UV and post-UV samples had relatively high concentrations of these viruses determined by qPCR. Infectious viruses were also observed in 98% of pre-UV samples and 76% of post-UV samples by cell culture, using either cytopathic effect (CPE) or integrated cell culture with qPCR (ICC-qPCR). Reovirus was the most common virus detected by ICC-qPCR, present in 92% of pre-UV and 48% of post-UV samples. Infectious enterovirus and adenovirus were detected by ICC-qPCR in 33% and 31% of pre-UV samples, 14% and 20% of post-UV samples, respectively. Mean log₁₀ reduction estimates for infectious reovirus was 1.2 and 1.8 log for the two WWTPs as assessed by ICC-qPCR, which was similar to the reduction of total infectious viruses (1.5 and 1.7 log) as assessed by CPE in cells culture. Overall, quantification of infectious reovirus appears to provide a useful index of enteric virus inactivation during wastewater treatment at full-scale. To our knowledge, this is the first comprehensive study to assess UV inactivation of human enteric viruses at full-scale in WWTPs using both molecular and cell culture techniques, providing important information for quantitative microbial risk assessment of UV inactivation of human viruses in municipal wastewater.

A dynamic transport model for quantification of norovirus internalization in lettuce from irrigation water and associated health risk

Food production using recycled wastewater offers a sustainable way forward in light of limited freshwater resources. However, concerns of food safety should be addressed to protect public health. To this end, we developed a dynamic transport model to track norovirus from the irrigation water to the root and shoot of lettuce during the growth period. These processes were embodied in a system of ordinary differential equations that also incorporated plant growth, transpiration rate, viral attachment and detachment to culture media, viral decay, and plant barrier effects. Model parameters were either obtained from the literature or through fitting the model to experimental data from a study reporting human norovirus transport in hydroponically grown lettuce. The results showed that lettuce grown hydroponically resulted in a higher risk than lettuce grown in soil. In both cases, the risk predicted failed to meet the risk benchmarks established by the U.S. EPA and WHO. Viral attachment to growth media, such as the soil particles, was an important mechanism for risk reduction. A sensitivity analysis revealed that harvesting time and irrigation time are important factors influencing the viral loads in lettuce. Hence, this pathogen transport model provides a framework for investigating the effects of time and other factors on disease burdens from water reuse in agriculture, underscoring the utility of a dynamic model. In the absence of a routine monitoring of contaminants in the recycled irrigation water and food crops, a quantitative risk assessment based on objective scientific knowledge is the best approach to guide the policy decisions on water reuse practices.

Temperature-Dependent Nanomechanics and Topography of Bacteriophage T7

Viruses are nanoscale infectious agents which may be inactivated by heat treatment. The global molecular mechanisms of virus inactivation and the thermally induced structural changes in viruses are not fully understood. In this study, we measured the heat-induced changes in the properties of T7 bacteriophage particles exposed to a two-stage (65°C and 80°C) thermal effect, by using atomic force microscopy (AFM)-based nanomechanical and topographical measurements. We found that exposure to 65°C led to the release of genomic DNA and to the loss of the capsid tail; hence, the T7 particles became destabilized. Further heating to 80°C surprisingly led to an increase in mechanical stability, due likely to partial denaturation of the capsomeric proteins kept within the global capsid arrangement.IMPORTANCE Even though the loss of DNA, caused by heat treatment, destabilizes the T7 phage, its capsid is remarkably able to withstand high temperatures with a more or less intact global topographical structure. Thus, partial denaturation within the global structural constraints of the viral capsid may have a stabilizing effect. Understanding the structural design of viruses may help in constructing artificial nanocapsules for the packaging and delivery of materials under harsh environmental conditions.

Nucleic Acid Photolysis by UV254 and the Impact of Virus Encapsidation

Determining the influence of higher order structure on UVC photolysis will help inform predictions of nucleic acid fate and microorganism inactivation. We measured the direct UV₂₅₄ photolysis kinetics of four model viral genomes composed of single-stranded and double-stranded RNA (ssRNA and dsRNA, respectively), as well as single-stranded and double-stranded DNA (ssDNA and dsDNA, respectively), in ultrapure water, in phosphate buffered saline (PBS), and encapsidated in their native virus particles. The photolysis rate constants of naked nucleic acids measured by qPCR (RT-qPCR for RNA) and normalized by the number of bases measured in a particular sequence exhibited the following trend: ssDNA > ssRNA ≈ dsDNA > dsRNA. In PBS, naked ssRNA bases reacted, on average, 24× faster than the dsRNA bases, whereas naked ssDNA bases reacted 4.3× faster than dsDNA bases. Endogenous indirect photolysis involving ¹O₂ and ·OH was ruled out as a major contributing factor in the reactions. A comparison of our measured rate constants with rate constants reported in the literature shows a general agreement among the nucleic acid UV₂₅₄ direct photolysis kinetics. Our results underscore the high resistance of dsRNA to UVC photolysis and demonstrate the role that nucleic acid structure and solution chemistry play in photoreactivity.

An integrated cell absorption process and quantitative PCR assay for the detection of the infectious virus in water

Here we developed an integrated cell absorption process and quantitative (reverse transcription) polymerase chain reaction (ICAP-q(RT)PCR) assay to detect infectious viruses, which based on the detection of the viral nucleic acid (RNA or DNA) in the early stage of viral attachment and entry towards cells. The results showed that the poliovirus or adenovirus whose concentration was as low as 0.2 TCID₅₀/mL could be detected by ICAP-q(RT)PCR after 4 h incubation. The ICAP-q(RT)PCR exhibited much higher sensitivity than the plaque assay. In parallel, it took shorter time to detect the viruses towards field samples compared with the integrated cell culture (ICC)-qPCR, but could still get the consistent detecting results with ICC-qPCR. This method is verified by detecting four different kinds of viruses including poliovirus, adenovirus, rotavirus, and astrovirus, which existed in the actual water samples. Among all the 24 Jinhe river samples, 50% (12/24) of river water samples were positive for poliovirus when detected by ICAP-q(RT)PCR, which was in accordance with the results detected by ICC-qPCR. However, 21% (5/24) and 68% (18/24) of the samples were detected to be positive for poliovirus by the plaque counting and the direct qPCR method, respectively. Compared with ICAP-q(PT)PCR and ICC-qPCR, the detecting results of qPCR or plaque assay displayed a marked expansion or decline, respectively, which lead to the evident deviations in the accuracy. The results demonstrated that our developed ICAP-q(RT)PCR method could dramatically reduce the test duration and quite improve the sensitivity towards infectious viruses. Therefore, the ICAP-q(RT)PCR method could be an effective and quantitative tool for detecting infectious viruses in water environments.

Irrigating Lettuce with Wastewater Effluent: Does Disinfection with Chlorine Dioxide Inactivate Viruses?

Reclaimed water obtained from urban wastewater is currently being used as irrigation water in water-scarce regions in Spain. However, wastewater can contain enteric viruses that water reclamation treatment cannot remove or inactivate completely. In the present study, greenhouse-grown baby lettuce ( L.) was irrigated with secondary treatment effluent from a wastewater treatment plant untreated and treated using chlorine dioxide (ClO). The effect of ClO treatment on the physicochemical characteristics and the presence of enteric viruses in irrigation water and lettuce was assessed. The presence of human noroviruses genogroups I and II (NoV GI and NoV GII), and human astroviruses (HAstV), was analyzed by real-time polymerase chain reaction (RT-qPCR). Additionally, to check for the loss of infectivity induced by the disinfection treatment, positive samples were re-analyzed after pretreatment with the intercalating dye PMAxx before RNA extraction and RT-qPCR. There were no significant differences in the proportion of positive samples and the concentration of enteric viruses between treated and untreated reclaimed water without PMAxx pretreatment ( > 0.05). A significantly lower concentration of NoV GI was detected in ClO-treated water when samples were pretreated with PMAxx ( < 0.05), indicating that inactivation was due to the disinfection treatment. Laboratory-scale validation tests indicated the suitability of PMAxx-RT-qPCR for discrimination between potentially infectious and ClO-damaged viruses. Although the applied ClO treatment was not able to significantly reduce the enteric virus load of the secondary effluent from the wastewater treatment plant, none of the lettuce samples analyzed ( = 36) was positive for the presence of NoV or HAstV.

Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches

Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280-320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems.

Assessment of recommended approaches for containment and safe handling of human excreta in emergency settings

Ebola and cholera treatment centres (ETC and CTC) generate considerable quantities of excreta that can further the transmission of disease amongst patients and health workers. Therefore, approaches for the safe handling, containment and removal of excreta within such settings are needed to minimise the likelihood of onward disease transmission. This study compared the performance and suitability of three chlorine-based approaches (0.5% HTH, NaDCC and NaOCl (domestic bleach)) and three lime-based approaches (10%, 20% and 30% Ca(OH)₂). The experiments followed recent recommendations for Ebola Treatment Centres. Three excreta matrices containing either raw municipal wastewater, or raw municipal wastewater plus 10% or 20% (w/v) added faecal sludge, were treated in 14 litre buckets at a ratio of 1:10 (chlorine solutions or lime suspensions: excreta matrix). The effects of mixing versus non-mixing and increasing contact time (10 and 30 mins) were also investigated. Bacterial (faecal coliforms (FC) and intestinal enterococci (IE)) and viral (somatic coliphages (SOMPH), F⁺specific phages (F+PH) and Bacteroides fragilis phages (GB-124PH)) indicators were used to determine the efficacy of each approach. Lime-based approaches provided greater treatment efficacy than chlorine-based approaches, with lime (30% w/v) demonstrating the greatest efficacy (log reductions values, FC = 4.75, IE = 4.16, SOMPH = 2.85, F+PH = 5.13 and GB124PH = 5.41). There was no statistical difference in efficacy between any of the chlorine-based approaches, and the highest log reduction values were: FC = 2.90, IE = 2.36, SOMPH = 3.01, F+PH = 2.36 and GB124PH = 0.74. No statistical difference was observed with respect to contact time for any of the approaches, and no statistical differences were observed with respect to mixing for the chlorine-based approaches. However, statistically significant increases in the efficacy of some lime-based approaches were observed following mixing. These findings provide evidence and practical advice to inform safe handling and containment of excreta and ensure more effective health protection in future emergency settings.

Reactivity of Enveloped Virus Genome, Proteins, and Lipids with Free Chlorine and UV254

The survivability of viruses in natural and engineered systems impacts public health. Inactivation mechanisms in the environment have been described for nonenveloped viruses, but it remains unclear how the membrane layer of enveloped viruses influences inactivation. We applied molecular tools and high-resolution mass spectrometry to measure reactions in the genome, proteins, and lipids of enveloped Pseudomonas phage Phi6 during inactivation by free chlorine and UV₂₅₄. Free chlorine readily penetrated the lipid membrane to react with proteins in the nucleocapsid and polymerase complex. The most reactive Phi6 peptides were approximately 150 times more reactive with free chlorine than the most reactive peptides reported in nonenveloped coliphage MS2. The inactivation kinetics of Phi6 by UV₂₅₄ was comparable with those of nonenveloped adenovirus and coliphage MS2 and were driven by UV₂₅₄ reactions with viral genomes. Our research identifies molecular features of an enveloped virus that are susceptible to chemical oxidants or UV radiation. Finally, the framework developed in the manuscript for studying molecular reactivities of Phi6 can be adopted to investigate enveloped virus survivability under various environmental conditions.

Free-Chlorine Disinfection as a Selection Pressure on Norovirus

Human noroviruses are excreted in feces from infected individuals and included in wastewater. It is critical to remove/inactivate them in wastewater treatment processes, particularly in the disinfection step, before release to aquatic environments. However, the high mutation rates of human noroviruses raise concerns about the emergence of strains that are less susceptible to disinfectants and can survive even after wastewater treatment. This study aimed to demonstrate the strain-dependent susceptibility of norovirus to free chlorine. A population originated from the murine norovirus strain S7-PP3, a surrogate for human noroviruses in environmental testing, was exposed to free chlorine and then propagated in a host cell. This cycle of free chlorine exposure followed by propagation in cells was repeated 10 times, and populations with lower susceptibility to free chlorine were obtained from two independent trials of chlorine exposure cycles. Open reading frame 2 (ORF2) and ORF3 of the murine norovirus genome were analyzed by next-generation sequencing, and a unique nonsynonymous mutation (corresponding to a change from phenylalanine to serine) at nucleotide (nt) 7280 in ORF3, which encodes the minor capsid protein VP2, was found in chlorine-exposed populations from both trials. It was confirmed that all of the clones from the chlorine-treated population had lower susceptibility to free chlorine than those from the control population. These results indicate that exposure to free chlorine and dilution exert different driving forces to form murine norovirus (MNV) quasispecies, and that there is a selective force to form MNV quasispecies under free chlorine exposure.IMPORTANCE This study showed that free chlorine disinfection exerted a selection pressure for murine norovirus (MNV). The strain-dependent viral susceptibility to the disinfectant elucidated in this study highlights the importance of employing less susceptible strains as representative viruses in disinfection tests, because the disinfection rate values obtained from more susceptible strains would be less useful in predicting the virus inactivation efficiency of circulating strains under practical disinfection conditions.

Effect of the Shellfish Proteinase K Digestion Method on Norovirus Capsid Integrity

Norovirus outbreaks are associated with the consumption of contaminated shellfish, and so efficient methods to recover and detect infectious norovirus in shellfish are important. The Proteinase K digestion method used to recover norovirus from shellfish, as described in the ISO 15216, would be a good candidate but its impact on the virus capsid integrity and thus infectivity was never examined. The aim of this study was to assess the impact of the Proteinase K digestion method, and of the heat treatment component of the method alone, on norovirus (genogroups I and II) and MS2 bacteriophage capsid integrity. A slightly modified version of the ISO method was used. RT-qPCR was used for virus detection following digestion of accessible viral RNA using RNases. MS2 phage infectivity was measured using a plaque assay. The effect of shellfish digestive glands (DG) on recovery was evaluated. In the presence of shellfish DG, a reduction in MS2 phage infectivity of about 1 log₁₀ was observed after the Proteinase K digestion method and after heat treatment component alone. For norovirus GII and MS2 phage, there was no significant loss of genome following the Proteinase K digestion method but there was a significant 0.24 log₁₀ loss of norovirus GI. In the absence of shellfish DG, the reduction in MS2 phage infectivity was about 2 log₁₀, with the addition of RNases resulting in a significant loss of genome for all tested viruses following complete Proteinase K digestion method and the heat treatment alone. While some protective effect from the shellfish DG on viruses was observed, the impact on capsid integrity and infectivity suggests that this method, while suitable for norovirus genome detection, may not completely preserve virus infectivity.

Cold argon-oxygen plasma species oxidize and disintegrate capsid protein of feline calicivirus

Possible mechanisms that lead to inactivation of feline calicivirus (FCV) by cold atmospheric-pressure plasma (CAP) generated in 99% argon-1% O₂ admixture were studied. We evaluated the impact of CAP exposure on the FCV viral capsid protein and RNA employing several cultural, molecular, proteomic and morphologic characteristics techniques. In the case of long exposure (2 min) to CAP, the reactive species of CAP strongly oxidized the major domains of the viral capsid protein (VP1) leading to disintegration of a majority of viral capsids. In the case of short exposure (15 s), some of the virus particles retained their capsid structure undamaged but failed to infect the host cells in vitro. In the latter virus particles, CAP exposure led to the oxidation of specific amino acids located in functional peptide residues in the P2 subdomain of the protrusion (P) domain, the dimeric interface region of VP1 dimers, and the movable hinge region linking the S and P domains. These regions of the capsid are known to play an essential role in the attachment and entry of the virus to the host cell. These observations suggest that the oxidative effect of CAP species inactivates the virus by hindering virus attachment and entry into the host cell. Furthermore, we found that the oxidative impact of plasma species led to oxidation and damage of viral RNA once it becomes unpacked due to capsid destruction. The latter effect most likely plays a secondary role in virus inactivation since the intact FCV genome is infectious even after damage to the capsid.

Plasmonic photocatalyst-like fluorescent proteins for generating reactive oxygen species

The recent advances in photocatalysis have opened a variety of new possibilities for energy and biomedical applications. In particular, plasmonic photocatalysis using hybridization of semiconductor materials and metal nanoparticles has recently facilitated the rapid progress in enhancing photocatalytic efficiency under visible or solar light. One critical underlying aspect of photocatalysis is that it generates and releases reactive oxygen species (ROS) as intermediate or final products upon light excitation or activation. Although plasmonic photocatalysis overcomes the limitation of UV irradiation, synthesized metal/semiconductor nanomaterial photocatalysts often bring up biohazardous and environmental issues. In this respect, this review article is centered in identifying natural photosensitizing organic materials that can generate similar types of ROS as those of plasmonic photocatalysis. In particular, we propose the idea of plasmonic photocatalyst-like fluorescent proteins for ROS generation under visible light irradiation. We recapitulate fluorescent proteins that have Type I and Type II photosensitization properties in a comparable manner to plasmonic photocatalysis. Plasmonic photocatalysis and protein photosensitization have not yet been compared systemically in terms of ROS photogeneration under visible light, although the phototoxicity and cytotoxicity of some fluorescent proteins are well recognized. A comprehensive understanding of plasmonic photocatalyst-like fluorescent proteins and their potential advantages will lead us to explore new environmental, biomedical, and defense applications.

Drinking Water Disinfection Byproducts (DBPs) and Human Health Effects: Multidisciplinary Challenges and Opportunities

While drinking water disinfection has effectively prevented waterborne diseases, an unintended consequence is the generation of disinfection byproducts (DBPs). Epidemiological studies have consistently observed an association between consumption of chlorinated drinking water with an increased risk of bladder cancer. Out of the >600 DBPs identified, regulations focus on a few classes, such as trihalomethanes (THMs), whose concentrations were hypothesized to correlate with the DBPs driving the toxicity of disinfected waters. However, the DBPs responsible for the bladder cancer association remain unclear. Utilities are switching away from a reliance on chlorination of pristine drinking water supplies to the application of new disinfectant combinations to waters impaired by wastewater effluents and algal blooms. In light of these changes in disinfection practice, this article discusses new approaches being taken by analytical chemists, engineers, toxicologists and epidemiologists to characterize the DBP classes driving disinfected water toxicity, and suggests that DBP exposure should be measured using other DBP classes in addition to THMs.

Identification of the inactivating factors and mechanisms exerted on MS2 coliphage in concentrated synthetic urine

Volume reduction (condensation) is a key for the practical usage of human urine as a fertilizer because it enables the saving of storage space and the reduction of transportation cost. However, concentrated urine may carry infectious disease risks resulting from human pathogens frequently present in excreta, though the survival of pathogens in concentrated urine is not well understood. In this study, the inactivation of MS2 coliphage, a surrogate for single-stranded RNA human enteric viruses, in concentrated synthetic urine was investigated. The infectious titer reduction of MS2 coliphage in synthetic urine samples was measured by plaque assay, and the reduction of genome copy number was monitored by reverse transcription-quantitative PCR (RTqPCR). Among chemical-physical conditions such as pH and osmotic pressure, uncharged ammonia was shown to be the predominant factor responsible for MS2 inactivation, independently of urine concentration level. The reduction rate of the viral genome number varied among genome regions, but the comprehensive reduction rate of six genome regions was well correlated with that of the infectious titer of MS2 coliphage. This indicates that genome degradation is the main mechanism driving loss of infectivity, and that RT-qPCR targeting the six genome regions can be used as a culture-independent assay for monitoring infectivity loss of the coliphage in urine. MS2 inactivation rate constants were well predicted by a model using ion composition and speciation in synthetic urine samples, which suggests that MS2 infectivity loss can be estimated solely based on the solution composition, temperature and pH, without explicitly accounting for effects of osmotic pressure.

Reduction of Human Norovirus GI, GII, and Surrogates by Peracetic Acid and Monochloramine in Municipal Secondary Wastewater Effluent

The objective of this study was to characterize human norovirus (hNoV) GI and GII reductions during disinfection by peracetic acid (PAA) and monochloramine in secondary wastewater (WW) and phosphate buffer (PB) as assessed by reverse transcription-qPCR (RT-qPCR). Infectivity and RT-qPCR reductions are also presented for surrogate viruses murine norovirus (MNV) and bacteriophage MS2 under identical experimental conditions to aid in interpretation of hNoV molecular data. In WW, RT-qPCR reductions were less than 0.5 log₁₀ for all viruses at concentration-time (CT) values up to 450 mg-min/L except for hNoV GI, where 1 log₁₀ reduction was observed at CT values of less than 50 mg-min/L for monochloramine and 200 mg-min/L for PAA. In PB, hNoV GI and MNV exhibited comparable resistance to PAA and monochloramine with CT values for 2 log₁₀ RT-qPCR reduction between 300 and 360 mg-min/L. Less than 1 log₁₀ reduction was observed for MS2 and hNoV GII in PB at CT values for both disinfectants up to 450 mg-min/L. Our results indicate that hNoVs exhibit genogroup dependent resistance and that disinfection practices targeting hNoV GII will result in equivalent or greater reductions for hNoV GI. These data provide valuable comparisons between hNoV and surrogate molecular signals that can begin the process of informing regulators and engineers on WW treatment plant design and operational practices necessary to inactivate hNoVs.

Climate change-induced increases in precipitation are reducing the potential for solar ultraviolet radiation to inactivate pathogens in surface waters

Climate change is accelerating the release of dissolved organic matter (DOM) to inland and coastal waters through increases in precipitation, thawing of permafrost, and changes in vegetation. Our modeling approach suggests that the selective absorption of ultraviolet radiation (UV) by DOM decreases the valuable ecosystem service wherein sunlight inactivates waterborne pathogens. Here we highlight the sensitivity of waterborne pathogens of humans and wildlife to solar UV, and use the DNA action spectrum to model how differences in water transparency and incident sunlight alter the ability of UV to inactivate waterborne pathogens. A case study demonstrates how heavy precipitation events can reduce the solar inactivation potential in Lake Michigan, which provides drinking water to over 10 million people. These data suggest that widespread increases in DOM and consequent browning of surface waters reduce the potential for solar UV inactivation of pathogens, and increase exposure to infectious diseases in humans and wildlife.

Enzymatic and viability RT-qPCR assays for evaluation of enterovirus, hepatitis A virus and norovirus inactivation: Implications for public health risk assessment

AIM

To assess the potential of a viability dye and an enzymatic reverse transcription quantitative PCR (RT-qPCR) pretreatment to discriminate between infectious and noninfectious enteric viruses.

METHODS AND RESULTS

Enterovirus (EntV), norovirus (NoV) GII.4 and hepatitis A virus (HAV) were inactivated at 95°C for 10 min, and four methods were used to compare the efficiency of inactivation: (i) cell culture plaque assay for HAV and EntV, (ii) RT-qPCR alone, (iii) RT-qPCR assay preceded by RNase treatment, and (iv) pretreatment with a viability dye (reagent D (RD)) followed by RT-qPCR. In addition, heat-inactivated NoV was treated with RD coupled with surfactants to increase the efficiency of the viability dye. No treatment was able to completely discriminate infectious from noninfectious viruses. RD-RT-qPCR reduced more efficiently the detection of noninfectious viruses with little to no removal observed with RNase. RD-RT-qPCR method was the closest to cell culture assay. The combination of surfactants and RD did not show relevant improvements on the removal of inactivated viruses signal compared with viability RT-qPCR, with the exception of Triton X-100.

CONCLUSION

The use of surfactant/RD-RT-qPCR, although not being able to completely remove the signal from noninfectious viral particles, yielded a better estimation of viral infectivity.

SIGNIFICANCE AND IMPACT OF THE STUDY

Surfactant/RD-RT-qPCR may be an advantageous tool for a better detection of infectious viruses with potential significant impact in the risk assessment of the presence of enteric viruses.

Iron oxide-mediated semiconductor photocatalysis vs. heterogeneous photo-Fenton treatment of viruses in wastewater. Impact of the oxide particle size

The photo-Fenton process is recognized as a promising technique towards microorganism disinfection in wastewater, but its efficiency is hampered at near-neutral pH operating values. In this work, we overcome these obstacles by using the heterogeneous photo-Fenton process as the default disinfecting technique, targeting MS2 coliphage in wastewater. The use of low concentrations of iron oxides in wastewater without H₂O₂ (wüstite, maghemite, magnetite) has demonstrated limited semiconductor-mediated MS2 inactivation. Changing the operational pH and the size of the oxide particles indicated that the isoelectric point of the iron oxides and the active surface area are crucial in the success of the process, and the possible underlying mechanisms are investigated. Furthermore, the addition of low amounts of Fe-oxides (1mgL^-1) and H₂O₂ in the system (1, 5 and 10mgL^-1) greatly enhanced the inactivation process, leading to heterogeneous photo-Fenton processes on the surface of the magnetically separable oxides used. Additionally, photo-dissolution of iron in the bulk, lead to homogeneous photo-Fenton, further aided by the complexation by the dissolved organic matter in the solution. Finally, we assess the impact of the presence of the bacterial host and the difference caused by the different iron sources (salts, oxides) and the Fe-oxide size (normal, nano-sized).

Cross-Resistance of UV- or Chlorine Dioxide-Resistant Echovirus 11 to Other Disinfectants

The emergence of waterborne viruses with resistance to disinfection has been demonstrated in the laboratory and in the environment. Yet, the implications of such resistance for virus control remain obscure. In this study we investigate if viruses with resistance to a given disinfection method exhibit cross-resistance to other disinfectants. Chlorine dioxide (ClO₂)- or UV-resistant populations of echovirus 11 were exposed to five inactivating treatments (free chlorine, ClO₂, UV radiation, sunlight, and heat), and the extent of cross-resistance was determined. The ClO₂-resistant population exhibited cross-resistance to free chlorine, but to none of the other inactivating treatments tested. We furthermore demonstrated that ClO₂ and free chlorine act by a similar mechanism, in that they mainly inhibit the binding of echovirus 11 to its host cell. As such, viruses with host binding mechanisms that can withstand ClO₂ treatment were also better able to withstand oxidation by free chlorine. Conversely, the UV-resistant population was not significantly cross-resistant to any other disinfection treatment. Overall, our results indicate that viruses with resistance to multiple disinfectants exist, but that they can be controlled by inactivating methods that operate by a distinctly different mechanism. We therefore suggest to utilize two disinfection barriers that act by different mechanisms in order to control disinfection-resistant viruses.

Resistance of Echovirus 11 to ClO2 Is Associated with Enhanced Host Receptor Use, Altered Entry Routes, and High Fitness

Waterborne viruses can exhibit resistance to common water disinfectants, yet the mechanisms that allow them to tolerate disinfection are poorly understood. Here, we generated echovirus 11 (E11) with resistance to chlorine dioxide (ClO₂) by experimental evolution, and we assessed the associated genotypic and phenotypic traits. ClO₂ resistance emerged after E11 populations were repeatedly reduced (either by ClO₂-exposure or by dilution) and then regrown in cell culture. The resistance was linked to an improved capacity of E11 to bind to its host cells, which was further attributed to two potential causes: first, the resistant E11 populations possessed mutations that caused amino acid substitutions from ClO₂-labile to ClO₂-stable residues in the viral proteins, which likely increased the chemical stability of the capsid toward ClO₂. Second, resistant E11 mutants exhibited the capacity to utilize alternative cell receptors for host binding. Interestingly, the emergence of ClO₂ resistance resulted in an enhanced replicative fitness compared to the less resistant starting population. Overall this study contributes to a better understanding of the mechanism underlying disinfection resistance in waterborne viruses, and processes that drive resistance development.

Zebrafish embryo toxicity of 15 chlorinated, brominated, and iodinated disinfection by-products

Disinfection to protect human health occurs at drinking water and wastewater facilities through application of non-selective oxidants including chlorine. Oxidants also transform organic material and form disinfection by-products (DBPs), many of which are halogenated and cyto- and genotoxic. Only a handful of assays have been used to compare DBP toxicity, and researchers are unsure which DBP(s) drive the increased cancer risk associated with drinking chlorinated water. The most extensive data set employs an in vitro model cell, Chinese hamster ovary cells. Traditionally, most DBP research focuses on the threat to human health, but the effects on aquatic species exposed to DBPs in wastewater effluents remain ill defined. We present the developmental toxicity for 15 DBPs and a chlorinated wastewater to a model aquatic vertebrate, zebrafish. Mono-halogenated DBPs followed the in vivo toxicity rank order: acetamides>acetic acids>acetonitriles~nitrosamines, which agrees well with previously published mammalian in vitro data. Di- and tri-halogenated acetonitriles were more toxic than their mono-halogenated analogues, and bromine- and iodine-substituted DBPs tended to be more toxic than chlorinated analogues. No zebrafish development effects were observed after exposure to undiluted or non-concentrated, chlorinated wastewater. We find zebrafish development to be a viable in vivo alternative or confirmatory assay to mammalian in vitro cell assays.

The Effect of Heat and Free Chlorine Treatments on the Surface Properties of Murine Norovirus

Heat and free chlorine are among the most efficient and commonly used treatments to inactivate enteric viruses, but their global inactivation mechanisms have not been elucidated yet. These treatments have been shown to affect at least the capsid proteins of viruses and thus may affect the surface properties (i.e. electrostatic charge and hydrophobicity) of such particles. Our aim was to study the effects of heat and free chlorine on surface properties for a murine norovirus chosen as surrogate for human norovirus. No changes in the surface properties were observed with our methods for murine norovirus exposed to free chlorine. Only the heat treatment led to major changes in the surface properties of the virus with the expression of hydrophobic domains at the surface of the particles after exposure to a temperature of 55 °C. No modification of the expression of hydrophobic domains occurred after exposure to 60 °C, and the low hydrophobic state exhibited by infectious and inactivated particles after exposure to 60 °C appeared to be irreversible for inactivated particles only, which may provide a means to discriminate infectious from inactivated murine noroviruses. When exposed to a temperature of 72 °C or to free chlorine at a concentration of 50 mg/L, the genome became available for RNases.

Selection of a Biosafety Level 1 (BSL-1) surrogate to evaluate surface disinfection efficacy in Ebola outbreaks: Comparison of four bacteriophages

The 2014 West African Ebola virus disease outbreak was the largest to date, and conflicting, chlorine-based surface disinfection protocols to interrupt disease transmission were recommended. We identified only one study documenting surface disinfection efficacy against the Ebola virus, showing a >6.6 log reduction after 5-minute exposure to 0.5% sodium hypochlorite (NaOCl) based on small-scale tests (Cook et al. (2015)). In preparation for future extensive, large-scale disinfection efficacy experiments, we replicated the Cook et al. experiment using four potential BSL-1 surrogates selected based on similarities to the Ebola virus: bacteriophages MS2, M13, Phi6, and PR772. Each bacteriophage was exposed to 0.1% and 0.5% NaOCl for 1, 5, and 10 minutes on stainless steel. MS2 and M13 were only reduced by 3.4 log and 3.5 log after a 10-minute exposure to 0.5% NaOCl, and would be overly conservative surrogates. Conversely, PR772 was too easily inactivated for surrogate use, as it was reduced by >4.8 log after only 1-minute exposure to 0.5% NaOCl. Phi6 was slightly more resistant than the Ebola virus, with 4.1 log reduction after a 5-minute exposure and not detected after a 10-minute exposure to 0.5% NaOCl. We therefore recommend Phi6 as a surrogate for evaluating the efficacy of chlorine-based surface disinfectants against the Ebola virus.

Laboratory biosafety for handling emerging viruses

Emerging viruses are viruses whose occurrence has risen within the past twenty years, or whose presence is likely to increase in the near future. Diseases caused by emerging viruses are a major threat to global public health. In spite of greater awareness of safety and containment procedures, the handling of pathogenic viruses remains a likely source of infection, and mortality, among laboratory workers. There is a steady increase in both the number of laboratories and scientist handling emerging viruses for diagnostics and research. The potential for harm associated to work with these infectious agents can be minimized through the application of sound biosafety concepts and practices. The main factors to the prevention of laboratory-acquired infection are well-trained personnel who are knowledgable and biohazard aware, who are perceptive of the various ways of transmission, and who are professional in safe laboratory practice management. In addition, we should emphasize that appropriate facilities, practices and procedures are to be used by the laboratory workers for the handling of emerging viruses in a safe and secure manner. This review is aimed at providing researchers and laboratory personnel with basic biosafety principles to protect themselves from exposure to emerging viruses while working in the laboratory. This paper focuses on what emerging viruses are, why emerging viruses can cause laboratory-acquired infection, how to assess the risk of working with emerging viruses, and how laboratory-acquired infection can be prevented. Control measures used in the laboratory designed as such that they protect workers from emerging viruses and safeguard the public through the safe disposal of infectious wastes are also addressed.

Comparative Inactivation of Murine Norovirus and MS2 Bacteriophage by Peracetic Acid and Monochloramine in Municipal Secondary Wastewater Effluent

Chlorination has long been used for disinfection of municipal wastewater (MWW) effluent while the use peracetic acid (PAA) has been proposed more recently in the United States. Previous work has demonstrated the bactericidal effectiveness of PAA and monochloramine in wastewater, but limited information is available for viruses, especially ones of mammalian origin (e.g., norovirus). Therefore, a comparative assessment was performed of the virucidal efficacy of PAA and monochloramine against murine norovirus (MNV) and MS2 bacteriophage in secondary effluent MWW and phosphate buffer (PB). A suite of inactivation kinetic models was fit to the viral inactivation data. Predicted concentration-time (CT) values for 1-log₁₀ MS2 reduction by PAA and monochloramine in MWW were 1254 and 1228 mg-min/L, respectively. The 1-, 2-, and 3-log₁₀ model predicted CT values for MNV viral reduction in MWW were 32, 47, and 69 mg-min/L for PAA and 6, 13, and 28 mg-min/L for monochloramine, respectively. Wastewater treatment plant disinfection practices informed by MS2 inactivation data will likely be protective for public health but may overestimate CT values for reduction of MNV. Additionally, equivalent CT values in PB resulted in greater viral reduction which indicate that viral inactivation data in laboratory grade water may not be generalizable to MWW applications.