Impact of the Heterogeneity in Free Chlorine, UV254, and Ozone Susceptibilities Among Coxsackievirus B5 on the Prediction of the Overall Inactivation Efficiency

Systematic investigation and modeling prediction of virus inactivation by ozone in wastewater: Decoupling the matrix effects

Water disinfection is undoubtedly regarded as a critical step in ensuring the water safety for human consumption, and ozone is widely used as a highly effective disinfectant for the control of pathogenic microorganisms in water. Although the diminished ozone efficiencies in complex water matrices have been widely reported, the specific extent to which individual components of matrix act on the virus inactivation by ozone remains unclear, and effective methodologies to predict the comprehensive effects of various factors are needed. In this study, the decoupled impact of the intricate water matrix on the ozone inactivation of viruses was systematically investigated and assessed from a simulative perspective. The concept of "equivalent ozone depletion rate constant" (k') was introduced to quantify the influence of different species, and a kinetic model was developed based on the k' values for simulating the ozone inactivation processes in complex matrix. The mechanisms through which diverse species influenced the ozone inactivation effectiveness were identified: 1) competition effects (k' = 105∼107 M-1s-1), including organic matters and reductive ions (SO32-, NO2-, and I-), which were the most influential species inhibiting the virus inactivation; 2) shielding effects (k' = 103∼104 M-1s-1), including Ca2+, Mg2+, and kaolin; 3) insignificant effects (k' = 0∼1 M-1s-1), including Cl-, SO42-, NO3-, NH4+, and Br-; 4) promotion effects (k' = ∼-103 M-1s-1), including CO32- and HCO3-. Prediction of ozone disinfection efficiency and evaluation of species contribution under complex aquatic matrices were successfully realized utilizing the model. The systematic understanding and methodologies developed in this research provide a reliable framework for predicting ozone inactivation efficiency under complex matrix, and a potential tool for accurate disinfectant dosage determination and interfering factors control in actual wastewater treatment processes.

Influence of Amino Acid Substitutions in Capsid Proteins of Coxsackievirus B5 on Free Chlorine and Thermal Inactivation

The sensitivity of enteroviruses to disinfectants varies among genetically similar variants and coincides with amino acid changes in capsid proteins, although the effect of individual substitutions remains unknown. Here, we employed reverse genetics to investigate how amino acid substitutions in coxsackievirus B5 (CVB5) capsid proteins affect the virus' sensitivity to free chlorine and heat treatment. Of ten amino acid changes observed in CVB5 variants with free chlorine resistance, none significantly reduced the chlorine sensitivity, indicating a minor role of the capsid composition in chlorine sensitivity of CVB5. Conversely, a subset of these amino acid changes located at the C-terminal region of viral protein 1 led to reduced heat sensitivity. Cryo-electron microscopy revealed that these changes affect the assembly of intermediate viral states (altered and empty particles), suggesting that the mechanism for reduced heat sensitivity could be related to improved molecular packing of CVB5, resulting in greater stability or altered dynamics of virus uncoating during infection.

Mitigation of viruses of concern and bacteriophage surrogates via common unit processes for water reuse: A meta-analysis

Water reuse is a growing global reality. In regulating water reuse, viruses have come to the fore as key pathogens due to high shedding rates, low infectious doses, and resilience to traditional wastewater treatments. To demonstrate the high log reductions required by emerging water reuse regulations, cost and practicality necessitate surrogates for viruses for use as challenge organisms in unit process evaluation and monitoring. Bacteriophage surrogates that are mitigated to the same or lesser extent than viruses of concern are routinely used for individual unit process testing. However, the behavior of these surrogates over a multi-barrier treatment train typical of water reuse has not been well-established. Toward this aim, we performed a meta-analysis of log reductions of common bacteriophage surrogates for five treatment processes typical of water reuse treatment trains: advanced oxidation processes, chlorination, membrane filtration, ozonation, and ultraviolet (UV) disinfection. Robust linear regression was applied to identify a range of doses consistent with a given log reduction of bacteriophages and viruses of concern for each treatment process. The results were used to determine relative conservatism of surrogates. We found that no one bacteriophage was a representative or conservative surrogate for viruses of concern across all multi-barrier treatments (encompassing multiple mechanisms of virus mitigation). Rather, a suite of bacteriophage surrogates provides both a representative range of inactivation and information about the effectiveness of individual processes within a treatment train. Based on the abundance of available data and diversity of virus treatability using these five key water reuse treatment processes, bacteriophages MS2, phiX174, and Qbeta were recommended as a core suite of surrogates for virus challenge testing.

Inactivation Kinetics and Replication Cycle Inhibition of Coxsackievirus B5 by Free Chlorine

The kinetics of coxsackievirus serotype B5 (CVB5) inactivation with free chlorine is characterized over a range of pH and temperature relevant to drinking water treatment with the primary goal of selecting experimental conditions used for assessing inactivation mechanisms. The inactivation kinetics identified in our study is similar to or slower than experimental data reported in the literature and thus provides a conservative representation of the kinetics of CVB5 inactivation for free chlorine that could be useful in developing future regulations for waterborne viral pathogens including adequate disinfection treatment for CVB5. Untreated and free chlorine-treated viruses, and host cells synchronized-infected with these viruses, are analyzed by a reverse transcription-quantitative polymerase chain reaction (RT-qPCR) method with the goal of quantitatively investigating the effect of free chlorine exposure on viral genome integrity, attachment to host cell, and viral genome replication. The inactivation kinetics observed results from a combination of hindering virus attachment to the host cell, inhibition of one or more subsequent steps of the replication cycle, and possibly genome damage.

Observed Kinetics of Enterovirus Inactivation by Free Chlorine Are Host Cell-Dependent

Virucidal efficacies of disinfectants are typically assessed by infectivity assay utilizing a single type of host cell. Enteroviruses infect multiple host cells via various entry routes, and each entry route may be impaired differently by a given disinfectant. Yet, it is unknown how the choice of host cells affects the observed inactivation kinetics. Here, we evaluated the inactivation kinetics of echovirus 11 (E11) by free chlorine, ultraviolet (UV) irradiation, and heat, using three different host cells (BGMK, RD, and A549). Inactivation rates were independent of the host cell for treatment of E11 by UV or heat. Conversely, E11 inactivation by free chlorine occurred 2-fold faster when enumerated on BGMK cells compared with RD and A549 cells. Host cell-dependent inactivation kinetics by free chlorine were also observed for echovirus 7, 9, and 13, and coxsackievirus A9. E11 inactivation by free chlorine was partly caused by a loss in host cell attachment, which was most pronounced for BGMK cells. BGMK cells lack the attachment receptor CD55 and a key subunit of the uncoating receptor β2M, which may contribute to the differential inactivation kinetics for this cell type. Consequently, inactivation kinetics of enteroviruses should be assessed using host cells with different receptor profiles.

Inactivation of coxsackievirus B5 by free chlorine under conditions relevant to drinking water treatment

Chlorine disinfection is commonly applied to inactivate pathogenic viruses in drinking water treatment plants. However, the role of water quality in chlorine disinfection of viruses has not been investigated thoughtfully. In this study, we investigated the inactivation efficiency of coxsackievirus B5 (CVB5) by free chlorine using actual water samples collected from four full-scale drinking water treatment plants in Japan under strict turbidity management (less than 0.14 NTU) over a 12-month period. It was found that chlorine disinfection of CVB5 might not be affected by water quality. Japanese turbidity management might play an indirect role in controlling the efficiency of chlorine disinfection.

Superiority of UV222 radiation by in situ aquatic electrode KrCl excimer in disinfecting waterborne pathogens: Mechanism and efficacy

Microbial safety in water has always been the focus of attention, especially during the COVID-19 pandemic. Development of green, efficient and safe disinfection technology is the key to control the spread of pathogenic microorganisms. Here, an in situ aquatic electrode KrCl excimer radiation with main emission wavelength 222 nm (UV222) was designed and used to disinfect model waterborne virus and bacteria, i.e. phage MS2, E. coli and S. aureus. High inactivation efficacy and diversity of inactivation mechanisms of UV222 were proved by comparision with those of commercial UV254. UV222 could totally inactivate MS2, E. coli and S. aureus with initial concentrations of ∼10⁷ PFU or CFU mL^-1 within 20, 15, and 36 mJ/cm², respectively. The UV dose required by UV254 to inactivate the same logarithmic pathogenic microorganism is at least twice that of UV222. The protein, genomic and cell membrane irreparable damage contributed to the microbial inactivation by UV222, but UV254 only act on nucleic acid of the target microorganisms. We found that UV222 damage nucleic acid with almost the same or even higher efficacy with UV254. In addition, free base damage of UV222 in similar ways with UV254(dimer and hydrate). But due to the quantum yield of free base degradation of UV222 was greater than UV254, the photolysis rates of UV222 to A, G, C and U four bases were 11.5, 1.2, 3.2 and 1 times as those of UV254, respectively. Excellent disinfection performance in UV222 irradiation was also achieved in real water matrices (WWTP and Lake). In addition, it was proved that coexisting HCO₃^- or HPO₄^{2 -} in real and synthetic water matrices can produce • OH to promote UV222 disinfection. This study provided novel insight into the UV222 disinfection process and demonstrated its possibility to take place of the conventional ultraviolet mercury lamp in water purification.

Investigation of removal and inactivation efficiencies of human sapovirus in drinking water treatment processes by applying an in vitro cell-culture system

Here, we examined the efficiencies of drinking water treatment processes for the removal and inactivation of human sapovirus (HuSaV). We applied a recently developed in vitro cell-culture system to produce purified solutions of HuSaV containing virus concentrations high enough to conduct virus-spiking experiments, to develop an integrated cell culture-polymerase chain reaction (ICC-PCR) assay to quantify the infectivity of HuSaV, and to conduct virus-spiking experiments. In virus-spiking coagulation-sedimentation-rapid sand filtration (CS-RSF) and coagulation-microfiltration (C-MF) experiments, HuSaV removals of 1.6-3.7-log₁₀ and 1.2->4.3-log₁₀, respectively, were observed. The removal ratios observed with CS-RSF were comparable and correlated with those of murine norovirus (MNV, a widely used surrogate for human noroviruses) and pepper mild mottle virus (PMMoV, a potential surrogate for human enteric viruses in physical and physicochemical drinking water treatment processes), and those observed with C-MF were higher than but still correlated with those of MNV and PMMoV, indicating that MNV and PMMoV are both potential surrogates for HuSaV in CS-RSF and C-MF. For astrovirus (AstV, a representative human enteric virus), removal ratios of 1.8-3.3-log₁₀ and 1.1->4.0-log₁₀ were observed with CS-RSF and C-MF, respectively. The removal ratios of AstV observed with CS-RSF were comparable and correlated with those of PMMoV, and those observed with C-MF were higher than but still correlated with those of PMMoV, indicating that PMMoV is a potential surrogate for AstV in CS-RSF and C-MF. When the efficacy of chlorine treatment was examined by using the developed ICC-PCR assay, 3.8-4.0-log₁₀ inactivation of HuSaV was observed at a CT value (free-chlorine concentration [C] multiplied by contact time [T]) of 0.02 mg-Cl₂·min/L. The infectivity reduction ratios of HuSaV were comparable with those of MNV. For AstV, 1.3-1.7-log₁₀ and >3.4-log₁₀ inactivation, as evaluated by ICC-PCR, was observed at CT values of 0.02 and 0.09 mg-Cl₂·min/L, respectively. These results indicate that HuSaV and AstV are both highly sensitive to chlorine treatment and more sensitive than a chlorine-resistant virus, coxsackievirus B5 (1.3-log₁₀ inactivation at a CT value of 0.4 mg-Cl₂·min/L, as evaluated by the ICC-PCR assay).

Ozone based inactivation and disinfection in the pandemic time and beyond: Taking forward what has been learned and best practice

The large-scale global COVID-19 has a profound impact on human society. Timely and effectively blocking the virus spread is the key to controlling the pandemic growth. Ozone-based inactivation and disinfection techniques have been shown to effectively kill SARS-CoV-2 in water, aerosols and on solid surface. However, the lack of an unified information and discussion on ozone-based inactivation and disinfection in current and previous pandemics and the absence of consensus on the main mechanisms by which ozone-based inactivation of pandemic causing viruses have hindered the possibility of establishing a common basis for identifying best practices in the utilization of ozone technology. This article reviews the research status of ozone (O3) disinfection on pandemic viruses (especially SARS-CoV-2). Taking sterilization kinetics as the starting point while followed by distinguishing the pandemic viruses by enveloped and non-enveloped viruses, this review focuses on analyzing the scope of application of the sterilization model and the influencing factors from the experimental studies and data induction. It is expected that the review could provide an useful reference for the safe and effective O3 utilization of SARS-CoV-2 inactivation in the post-pandemic era.

Continuous inactivation of human adenoviruses in water by a novel g-C3N4/WO3/biochar memory photocatalyst under light-dark cycles

Viruses transmitted by water have raised considerable concerns for public health. A novel memory photocatalyst of g-C₃N₄/WO₃/biochar was successfully developed for effective inactivation of human adenoviruses (HAdVs) in water, in which WO₃ as an electron-storage reservoir and biochar as an electron shuttle is employed to synergistically improve photocatalytic activity of g-C₃N₄. The tertiary composite exhibited continuous photocatalytic performance for HAdVs inactivation without regrowth in water under light-dark cycles, i.e., ∼3.9-log inactivation under 6-h visible light irradiation and an additional ∼1.1-log inactivation under the following 6-h dark. The enhanced virucidal mechanism was attributed to the heterojunction formation and especially the electron-transfer pathway switching via biochar incorporation, contributing to electron transfer and storage in the light phase and then electron release in the dark phase, along with obviously increased generation of the virus-killing •OH radicals under light-dark cycles.

Combating coxsackievirus B infections

Coxsackieviruses B (CVB) are small, non-enveloped, single-stranded RNA viruses belonging to the Enterovirus genus of the Picornaviridae family. They are common worldwide and cause a wide variety of human diseases ranging from those having relatively mild symptoms to severe acute and chronic pathologies such as cardiomyopathy and type 1 diabetes. The development of safe and effective strategies to combat these viruses remains a challenge. The present review outlines current approaches to control CVB infections and associated diseases. Various drugs targeting viral or host proteins involved in viral replication as well as vaccines have been developed and shown potential to prevent or combat CVB infections in vitro and in vivo in animal models. Repurposed drugs and alternative strategies targeting miRNAs or based on plant extracts and probiotics and their derivatives have also shown antiviral effects against CVB. In addition, clinical trials with vaccines and drugs are underway and offer hope for the prevention or treatment of CVB-induced diseases.

Genotype-dependent kinetics of enterovirus inactivation by free chlorine and ultraviolet (UV) irradiation

Inactivation kinetics of enterovirus by disinfection is often studied using a single laboratory strain of a given genotype. Environmental variants of enterovirus are genetically distinct from the corresponding laboratory strain, yet it is poorly understood how these genetic differences affect inactivation. Here we evaluated the inactivation kinetics of nine coxsackievirus B3 (CVB3), ten coxsackievirus B4 (CVB4), and two echovirus 11 (E11) variants by free chlorine and ultraviolet irradiation (UV). The inactivation kinetics by free chlorine were genotype- (i.e., susceptibility: CVB5 < CVB3 ≈ CVB4 < E11) and genogroup-dependent and exhibited up to 15-fold difference among the tested viruses. In contrast, only minor (up to 1.3-fold) differences were observed in the UV inactivation kinetics. The differences in variability between the two disinfectants could be rationalized by their respective inactivation mechanisms: inactivation by UV mainly depends on the genomic size and composition, which was similar for all viruses tested, whereas free chlorine targets the viral capsid protein, which exhibited critical differences between genogroups and genotypes. Finally, we integrated the observed variability in inactivation rate constants into an expanded Chick-Watson model to estimate the overall inactivation of an enterovirus consortium. The results highlight that the distribution of inactivation rate constants and the abundance of each genotype are essential parameters to accurately predict the overall inactivation of an enterovirus population by free chlorine. We conclude that predictions based on inactivation data of a single variant or reference pathogen alone likely overestimate the true disinfection efficiency of free chlorine.

Ozone disinfection of waterborne pathogens and their surrogates: A critical review

Viruses, Giardia cysts, and Cryptosporidium parvum oocysts are all major causes of waterborne diseases that can be uniquely challenging in terms of inactivation/removal during water and wastewater treatment and water reuse. Ozone is a strong disinfectant that has been both studied and utilized in water treatment for more than a century. Despite the wealth of data examining ozone disinfection, direct comparison of results from different studies is challenging due to the complexity of aqueous ozone chemistry and the variety of the applied approaches. In this systematic review, an analysis of the available ozone disinfection data for viruses, Giardia cysts, and C. parvum oocysts, along with their corresponding surrogates, was performed. It was based on studies implementing procedures which produce reliable and comparable datasets. Datasets were compiled and compared with the current USEPA Ct models for ozone. Additionally, the use of non-pathogenic surrogate organisms for prediction of pathogen inactivation during ozone disinfection was evaluated. Based on second-order inactivation rate constants, it was determined that the inactivation efficiency of ozone decreases in the following order: Viruses >> Giardia cysts > C. parvum oocysts. The USEPA Ct models were found to be accurate to conservative in predicting inactivation of C. parvum oocysts and viruses, respectively, however they overestimate inactivation of Giardia cysts at ozone Ct values greater than ∼1 mg min L-1. Common surrogates of these pathogens, such as MS2 bacteriophage and Bacillus subtilis spores, were found to exhibit different inactivation kinetics to mammalian viruses and C. parvum oocysts, respectively. The compilation of data highlights the need for further studies on disinfection kinetics and inactivation mechanisms by ozone to better fit inactivation models as well as for proper selection of surrogate organisms.

Experimental Adaptation of Murine Norovirus to Calcium Hydroxide

Slaked lime (calcium hydroxide) is a commonly used disinfectant for fecal sludge. Although viruses are inactivated by lime treatment, whether RNA viruses adapt to lime treatment has not yet been determined. Here, we show that murine norovirus developed higher tolerance during serial passages with lime treatment. We compared synonymous and non-synonymous nucleotide diversities of the three open reading frames of viral genome and revealed that virus populations were subjected to enhanced purifying selection over the course of serial passages with lime treatment. Virus adaptation to lime treatment was coincident with amino acid substitution of lysine to arginine at position 345 (K345R) on the major capsid protein VP1, which accounted for more than 90% of the population. The infectious clones with the K345R produced using a plasmid-based reverse genetics system exhibited greater tolerance in a lime solution, which indicated that the specific amino acid substitution was solely involved in the viral tolerance in lime treatment.