Long-range quantitative PCR for determining inactivation of adenovirus 2 by ultraviolet light

The effect of enzymatic and viability dye treatment in combination with long-range PCR on assessing Tulane virus infectivity

Human norovirus (HuNoV) is regularly involved in food-borne infections. To detect infectious HuNoV in food, RT-qPCR remains state of the art but also amplifies non-infectious virus. The present study combines pre-treatments, RNase and propidium monoazide, with three molecular analyses, including long-range PCR, to predominantly detect infectious Tulane virus (TuV), a culturable HuNoV surrogate. TuV was exposed to inactivating conditions to assess which molecular method most closely approximates the reduction in infectious virus determined by cell culture (TCID50). After thermal treatments (56 °C/5 min, 70 °C/5 min, 72 °C/20 min), TCID50 reductions of 0.3, 4.4 and 5.9 log10 were observed. UV exposure (40/100/1000 mJ/cm2) resulted in 1.1, 2.5 and 5.9 log10 reductions. Chlorine (45/100 mg/L for 1 h) reduced infectious TuV by 2.0 and 3.0 log10. After thermal inactivation standard RT-qPCR, especially with pre-treatments, showed the smallest deviation from TCID50. On average, RT-qPCR with pre-treatments deviated by 1.1-1.3 log10 from TCID50. For UV light, long-range PCR was closest to TCID50 results. Long-range reductions deviated from TCID50 by ≤0.1 log10 for mild and medium UV-conditions. However, long-range analyses often resulted in qPCR non-detects. At higher UV doses, RT-qPCR with pre-treatments differed by ≤1.0 log10 from TCID50. After chlorination the molecular methods repeatedly deviated from TCID50 by >1.0 log10, Overall, each method needs to be further optimized for the individual types of inactivation treatment.

A Multifaceted Approach for Evaluating Hepatitis E Virus Infectivity In Vitro: Cell Culture and Innovative Molecular Methods for Integrity Assessment

Hepatitis E virus is a prominent cause of viral hepatitis worldwide. In Western countries, most infections are asymptomatic. However, acute self-limiting hepatitis and chronic cases in immunocompromised individuals can occur. Studying HEV is challenging due to its difficulty to grow in cell culture. Consequently, the detection of the virus mainly relies on RT-qPCR, which cannot differentiate between infectious and non-infectious particles. To overcome this problem, methods assessing viral integrity offer a possible solution to differentiate between intact and damaged viruses. This study aims at optimizing existing HEV cell culture models and RT-qPCR-based assays for selectively detecting intact virions to establish a reliable model for assessing HEV infectivity. In conclusion, these newly developed methods hold promise for enhancing food safety by identifying approaches for inactivating HEV in food processing, thereby increasing food safety measures.

Assessment of novel antiviral filter using pseudo-type SARS-CoV-2 virus in fast air velocity vertical-type wind tunnel

Current evidence suggests that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can remain suspended spread in aerosols for longer period of time under poorly ventilated indoor setting. To minimize spreading, application of antiviral filter to capture infectious aerosols and to inactivate SARS-CoV-2 can be a promising solution. This study aimed to develop a method to assess simultaneously the filtration and removal efficiency of aerosolized pseudo-type SARS-CoV-2 using a vertical-type wind tunnel with relatively high face velocity (1.3 m/s). Comparing with the untreated spunlace non-woven filter, the C-POLAR™ treated filter increased the filtration efficiency from 74.2 ± 11.5% to 97.2 ± 1.7%, with the removal efficiency of 99.4 ± 0.051%. The results provided not only solid evidence to support the effectiveness of the cationic polymeric coated filter in fighting against the SARS-CoV-2 pandemic, but also a method to test viral filtration and removal efficiency under relative fast air velocity and with a safer environment to the operators.

Innovative nonthermal technologies for inactivation of emerging foodborne viruses

Various foodborne viruses have been associated with human health during the last decade, causing gastroenteritis and a huge economic burden worldwide. Furthermore, the emergence of new variants of infectious viruses is growing continuously. Inactivation of foodborne viruses in the food industry is a formidable task because although viruses cannot grow in foods, they can survive in the food matrix during food processing and storage environments. Conventional inactivation methods pose various drawbacks, necessitating more effective and environmentally friendly techniques for controlling foodborne viruses during food production and processing. Various inactivation approaches for controlling foodborne viruses have been attempted in the food industry. However, some traditionally used techniques, such as disinfectant-based or heat treatment, are not always efficient. Nonthermal techniques are considered a new platform for effective and safe treatment to inactivate foodborne viruses. This review focuses on foodborne viruses commonly associated with human gastroenteritis, including newly emerged viruses, such as sapovirus and Aichi virus. It also investigates the use of chemical and nonthermal physical treatments as effective technologies to inactivate foodborne viruses.

Integrating life cycle assessment with quantitative microbial risk assessment for a holistic evaluation of sewage treatment plant

An integrated approach was employed in the present study to combine life cycle assessment (LCA) with quantitative microbial risk assessment (QMRA) to assess an existing sewage treatment plant (STP) at Roorkee, India. The midpoint LCA modeling revealed that high electricity consumption (≈ 576 kWh.day^-1) contributed to the maximum environmental burdens. The LCA endpoint result of 0.01 disability-adjusted life years per person per year (DALYs pppy) was obtained in terms of the impacts on human health. Further, a QMRA model was developed based on representative sewage pathogens, including E. coli O157:H7, Giardia sp., adenovirus, norovirus, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The public health risk associated with intake of pathogen-laden aerosols during treated water reuse in sprinkler irrigation was determined. A cumulative health risk of 0.07 DALYs pppy was obtained, where QMRA risks contributed 86 % of the total health impacts. The annual probability of illness per person was highest for adenovirus and norovirus, followed by SARS-CoV-2, E. coli O157:H7 and Giardia sp. Overall, the study provides a methodological framework for an integrated LCA-QMRA assessment which can be applied across any treatment process to identify the hotspots contributing maximum environmental burdens and microbial health risks. Furthermore, the integrated LCA-QMRA approach could support stakeholders in the water industry to select the most suitable wastewater treatment system and establish regulations regarding the safe reuse of treated water.

Investigation on the applicability of a long-range reverse-transcription quantitative polymerase chain reaction assay for the rapid detection of active viruses

BACKGROUND

Although conventional polymerase chain reaction (PCR) methods are widely used in diagnosis, the titer of the pathogenic virus is difficult to determine based on the PCR. In our prior report, a long-range reverse-transcription quantitative PCR (LR-RT-qPCR) assay was developed to assess the titer of UV-irradiated influenza A virus (IAV) rapidly. In this research, we focused on whether the LR-RT-qPCR assay could evaluate the titer of IAV inactivated by other methods.

METHODS

IAV was inactivated by: heating at 100 °C for periods ranging from 1 to 15 min, treating with 0.12% sodium hypochlorite for periods ranging from 3 to 30 min, or treating with 70% ethanol for periods ranging from 10 to 30 min. Fifty percent tissue culture infectious dose (TCID₅₀) assay was performed to confirm the efficacy of the inactivation methods, followed by LR-RT-qPCR to investigate the correlation between infectivity and copy number.

RESULTS

One minute heating, 3 min sodium hypochlorite treatment, or 10 min ethanol treatment was sufficient to deactivate IAV. Changes before and after the inactivations in the copy numbers on LR-RT-qPCR were significantly different among the inactivation methods. Heat-inactivation drastically decreased the copy number to below the cutoff value around 5 copies/μL after 5 min treatment. The inactivation time of heating estimated using LR-RT-qPCR was marginally higher than that determined using TCID₅₀. However, the treatments with sodium hypochlorite or ethanol moderately and minimally affected the copy numbers obtained using LR-RT-qPCR (~ 1 digit or no copy number decrease), respectively.

CONCLUSIONS

In addition to good applicability in UV-irradiation previously reported, the LR-RT-qPCR method is suitable for evaluating the effect of heat-inactivation on IAV infectivity. However, minor modifications may be made and investigated in the future to reduce the time intervals with TCID₅₀. Although this method is not applicable for the ethanol inactivation, rapid evaluation of the effects of chlorination on IAV can be determined by comparing copy numbers before and after treatment using the LR-RT-qPCR method.

UV222 disinfection of SARS-CoV-2 in solution

There is an urgent need for evidence-based engineering controls to reduce transmission of SARS-CoV-2, which causes COVID-19. Although ultraviolet (UV) light is known to inactivate coronaviruses, conventional UV lamps contain toxic mercury and emit wavelengths (254 nm) that are more hazardous to humans than krypton chlorine excimer lamps emitting 222 nm (UV222). Here we used culture and molecular assays to provide the first dose response for SARS-CoV-2 solution exposed to UV222. Culture assays (plaque infectivity to Vero host) demonstrated more than 99.99% disinfection of SARS-CoV-2 after a UV222 dose of 8 mJ/cm2 (pseudo-first order rate constant = 0.64 cm2/mJ). Immediately after UV222 treatment, RT-qPCR assays targeting the nucleocapsid (N) gene demonstrated ~ 10% contribution of N gene damage to disinfection kinetics, and an ELISA assay targeting the N protein demonstrated no contribution of N protein damage to disinfection kinetics. Molecular results suggest other gene and protein damage contributed more to disinfection. After 3 days incubation with host cells, RT-qPCR and ELISA kinetics of UV222 treated SARS-CoV-2 were similar to culture kinetics, suggesting validity of using molecular assays to measure UV disinfection without culture. These data provide quantitative disinfection kinetics which can inform implementation of UV222 for preventing transmission of COVID-19.

The UV Dose Used for Disinfection of Drinking Water in Sweden Inadequately Inactivates Enteric Virus with Double-Stranded Genomes

Irradiation with ultraviolet light (UV) at 254 nm is effective in inactivating a wide range of human pathogens. In Sweden, a UV dose of 400 J/m² is often used for the treatment of drinking water. To investigate its effect on virus inactivation, enteric viruses with different genomic organizations were irradiated with three UV doses (400, 600, and 1000 J/m²), after which their viability on cell cultures was examined. Adenovirus type 2 (double-stranded DNA), simian rotavirus 11 (double-stranded RNA), and echovirus 30 (single-stranded RNA) were suspended in tap water and pumped into a laboratory-scale Aquada 1 UV reactor. Echovirus 30 was reduced by 3.6-log₁₀ by a UV dose of 400 J/m². Simian rotavirus 11 and adenovirus type 2 were more UV resistant with only 1-log₁₀ reduction at 400 J/m² and needed 600 J/m² for 2.9-log₁₀ and 3.1-log₁₀ reductions, respectively. There was no significant increase in the reduction of viral viability at higher UV doses, which may indicate the presence of UV-resistant viruses. These results show that higher UV doses than those usually used in Swedish drinking water treatment plants should be considered in combination with other barriers to disinfect the water when there is a risk of fecal contamination of the water.

UV inactivation of sewage isolated human adenovirus

Adenoviruses are known to be one of the most resistant viruses to UV disinfection. This study determined the inactivation kinetics of adenovirus freshly isolated from sewage samples, and compared the results with reference adenovirus stocks grown in the laboratory. Human adenoviruses were isolated from sewage samples using the HEK 293 cell line. Inactivation kinetics for UV irradiation was determined for monochromatic low pressure (LP) mercury UV lamp (254 nm) and polychromatic medium pressure (MP) mercury UV lamp for each sewage isolate. Eleven (11) isolates were obtained from nine (9) different sewage samples with most isolates belonging to the enteric adenovirus group, specifically adenovirus 41. The average dose required for 4 log inactivation using LP UV lamps for sewage isolates (220 mJ/cm²) was not significantly different (p > 0.1) from the average dose reported for lab-grown enteric adenovirus (179.6 mJ/cm²). Interestingly, the average dose required for 4 log inactivation using MP UV lamps was significantly higher (p = 0.004) for sewage isolates (124 mJ/cm²) when compared to the average dose reported for laboratory stocks of adenovirus 40 and 41 (71 mJ/cm²). Viral capsid analysis using the propidium monoazide (PMA)-qPCR method showed that adenovirus isolates from group F were less affected by exposure to MP UV Lamps than adenoviruses from group D and C. Adenovirus isolates obtained from sewage samples showed greater resistance to UV irradiation compared to laboratory grown strains, although required doses for MP UV were still considerably lower than LP UV. These data suggest that the required fluence for inactivation of adenoviruses in real-world waters may be higher than previously understood.

Inactivation mechanisms of human adenovirus by e-beam irradiation in water environments

This study aims to study the kinetics and mechanisms of human adenovirus inactivation by electron beam. Human adenovirus type 5 (HAdV-5) was inoculated in two types of aqueous substrates (phosphate-buffered saline - PBS, domestic wastewater - WW) treated by electron beam at a dose range between 3 and 21 kGy. Samples were evaluated for virus infectivity, PCR amplification of fragments of HAdV-5 genome and abundance and antigenicity of the virion structural proteins. The maximum reduction in viral titre, in plaque-forming units (PFU) per millilitre, was about 7 and 5 log PFU/mL for e-beam irradiation at 20 kGy in PBS and 19 kGy in wastewater, respectively. Among the virion structural proteins detected, the hexon protein showed the higher radioresistance. Long (10.1 kbp) genomic DNA fragments were differently PCR amplified, denoting a substrate effect on HAdV-5 genome degradation by e-beam. The differences observed between the two substrates can be explained by the protective effect that the organic matter present in the substrate may have on viral irradiation. According to the obtained results, the decrease in viral viability/infectivity may be due to DNA damage and to protein alterations. In summary, electron beam irradiation at a dose of 13 kGy is capable of reducing HAdV-5 viral titres by more than 99.99% (4 log PFU/mL) in both substrates assayed, indicating that this type of technology is effective for viral wastewater disinfection and may be used as a tertiary treatment in water treatment plants. KEY POINTS: • The substrate in which the virus is suspended has an impact on its sensitivity to e-beam treatment. • E-beam irradiation at 13 kGy is capable of reducing by 4 Log PFU/mL the HAdV-5 viral titre. • The decrease in viral viability/infectivity may be due to DNA damage and to protein alterations.

Investigation of mouse hepatitis virus strain A59 inactivation under both ambient and cold environments reveals the mechanisms of infectivity reduction following UVC exposure

The surface contamination of SARS-CoV-2 is becoming a potential source of virus transmission during the pandemic of COVID-19. Under the cold environment, the infection incidents would be more severe with the increase of virus survival time. Thus, the disinfection of contaminated surfaces in both ambient and cold environments is a critical measure to restrain the spread of the virus. In our study, it was demonstrated that the 254 nm ultraviolet-C (UVC) is an efficient method to inactivate a coronavirus, mouse hepatitis virus strain A59 (MHV-A59). The inactivation rate to MHV-A59 coronavirus was up to 99.99% when UVC doses were 2.90 and 14.0 mJ/cm² at room temperature (23 °C) and in cold environment (-20 °C), respectively. Further mechanistic study demonstrated that UVC could induce spike protein damage to partly impede virus attachment and genome penetration processes, which contributes to 12% loss of viral infectivity. Additionally, it can induce genome damage to significantly interrupt genome replication, protein synthesis, virus assembly and release processes, which takes up 88% contribution to viral inactivation. With these mechanistic understandings, it will greatly contribute to the prevention and control of the current SARS-CoV-2 transmissions in cold chains (low temperature-controlled product supply chains), public area such as airport, school, and warehouse.

Recent Update on UV Disinfection to Fulfill the Disinfection Credit Value for Enteric Viruses in Water

Ultraviolet (UV) radiation alone or in combination with other oxidation processes is increasingly being considered for water disinfection because of stringent regulatory requirements for pathogen inactivation. To fulfill this requirement, an appropriate UV dose or fluence (mJ/cm²) is applied to combat enteric viruses in surface or treated water. There is a need for a cumulative review on the effectiveness of current and emerging UV technologies against various types of human enteric viruses. We extracted the kinetics data from 52 selected experimental studies on enteric virus inactivation using low pressure (LP-UV), medium pressure (MP-UV), UV-LED, and advanced oxidation processes (AOPs) and applied a simple linear regression analysis to calculate the range of UV fluence (mJ/cm²) needed for 4-log₁₀ inactivation. The inactivation of adenoviruses with LP-UV, MP-UV, and UV/H₂O₂ (10 mg/L) required the highest fluence, which ranged from 159 to 337, 45, and 115 mJ/cm², respectively. By contrast, when using LP-UV, the inactivation of other enteric viruses, such as the Caliciviridae and Picornaviridae family and rotavirus, required fluence that ranged from 19 to 69, 18 to 43, and 38 mJ/cm², respectively. ssRNA viruses exhibit higher sensitivity to UV radiation than dsRNA and DNA viruses. In general, as an upgrade to LP-UV, MP-UV is a more promising strategy for eliminating enteric viruses compared to AOP involving LP-UV with added H₂O₂ or TiO₂. The UV-LED technology showed potential because a lower UV fluence (at 260 and/or 280 nm wavelength) was required for 4-log₁₀ inactivation compared to that of LP-UV for most strains examined in this critical review. However, more studies evaluating the inactivation of enteric viruses by means of UV-LEDs and UV-AOP are needed to ascertain these observations.

Prediction of Photolysis Kinetics of Viral Genomes under UV254 Irradiation to Estimate Virus Infectivity Loss

UV₂₅₄ irradiation disinfection is a commonly used method to inactivate pathogenic viruses in water and wastewater treatment. Model prediction method can serve as a pre-screening tool to quickly estimate the effectiveness of UV₂₅₄ irradiation on emerging or unculturable viruses. In this study, an improved prediction model was applied to estimate UV₂₅₄ photolysis kinetics of viral genomes (k_{pred, genome}) based on the genome sequences and their photoreactivity and to correlate with the experimental virus infectivity loss kinetics (k_{exp, infectivity}). The UV₂₅₄ inactivation data of 102 viruses (including 2 dsRNA, 65 ssRNA, 33 dsDNA and 2 ssDNA viruses) were collected from the published experimental data with k_{exp, infectivity} ranging from 0.016 to 3.49 cm² mJ^-1. The model had fairly good performance in predicting the virus susceptibility to UV₂₅₄ irradiation except dsRNA viruses (Pearson's correlation coefficient = 0.64) and 70% of k_{pred, genome} fell in the range of 1/2 to 2 times of k_{exp, infectivity}. The positive deviation of the model often occurred for photoresistant viruses with low k_{exp, infectivity} less than 0.20 cm² mJ^-1 (e.g., Adenovirus, Papovaviridae and Retroviridae). We also applied this model to predict the UV₂₅₄ inactivation rate of SARS-CoV-2 (k_{pred, genome} = 3.168 cm² mJ^-1) and a UV dose of 3 mJ cm^-2 seemed to be able to achieve a 2-log removal by conservative calculation using 1/2k_{pred, genome} value. This prediction method can be used as a prescreening tool to assess the effectiveness of UV₂₅₄ irradiation for emerging/unculturable viruses in water or wastewater treatment.

Comparison of faecal indicator and viral pathogen light and dark disinfection mechanisms in wastewater treatment pond mesocosms

This study compared light and dark disinfection of faecal bacteria/viral indicator organisms (E. coli and MS2 (fRNA) bacteriophage) and human viruses (Echovirus and Norovirus) in Wastewater Treatment Pond (WTP) mesocosms. Stirred pond mesocosms were operated in either outdoor sunlight-exposed or laboratory dark conditions in two experiments during the austral summer. To investigate wavelength-dependence of sunlight disinfection, three optical filters were used: (1) polyethylene film (light control: transmitting all solar UV and visible wavelengths), (2) acrylic (removing most UVB <315 nm), and (3) polycarbonate (removing both UVB and UVA <400 nm). To assess different dark disinfection processes WTP effluent was treated before spiking with target microbes, by (a) 0.22 μm filtration to remove all but colloidal particles, (b) 0.22 μm filtration followed by heat treatment to destroy enzymes, and (c) addition of Cytochalasin B to supress protozoan grazing. Microbiological stocks containing E. coli, MS2 phage, Echovirus, and Norovirus were spiked into each mesocosm 10 min before the experiments commenced. The light control exposed to all sunlight wavelengths achieved >5-log E. coli and MS2 phage removal (from ~1.0 × 10⁶ to <1 PFU/mL) within 3 h compared with up to 6 h in UV-filtered mesocosms. This result confirms that UVB contributes to inactivation of E. coli and viruses by direct sunlight inactivation. However, the very high attenuation with depth of UVB in WTP water (99% removal in the top 8 cm) suggests that UVB disinfection may be less important than other removal processes averaged over time and full-scale pond depth. Dark removal was appreciably slower than sunlight-mediated inactivation. The dark control typically achieved higher removal of E. coli and viruses than the 0.22 μm filtered (dark) mesocosms. This result suggests that adsorption of E. coli and viruses to WTP particles (e.g., algae and bacteria bio-flocs) is an important mechanism of dark disinfection, while bacteria and virus characteristics (e.g. surface charge) and environmental conditions can influence dark disinfection processes.

Greater than 3-Log Reduction in Viable Coronavirus Aerosol Concentration in Ducted Ultraviolet-C (UV-C) Systems

Control technologies to inactivate airborne viruses effectively are needed during the ongoing SARS-CoV-2 pandemic, and to guard against airborne transmitted diseases. We demonstrate that sealed UV-C flow reactors operating with fluences near 253 ± 1 nm of 13.9-49.6 mJ cm-2 efficiently inactivate coronaviruses in an aerosol. For measurements, porcine respiratory coronavirus (PRCV) was nebulized in a custom-built, 3.86 m wind tunnel housed in a biosafety level class II facility. The single pass log10 reduction of active coronavirus was in excess of 2.2 at a flow rate of 2439 L min-1 (13.9 mJ cm-2) and in excess of 3.7 (99.98% removal efficiency) at 684 L min-1 (49.6 mJ cm-2). Because virus titers resulting from sampling downstream of the UV-C reactor were below the limit of detection, the true log reduction is likely even higher than measured. Comparison of virus titration results to reverse transcriptase quantitative PCR and measurement of fluorescein concentrations (doped into the nebulized aerosol) reveals that the reduction in viable PRCV is primarily due to UV-C based inactivation, as opposed to physical collection of virus. The results confirm that UV-C flow reactors can efficiently inactivate coronaviruses through incorporation into HVAC ducts or recirculating air purifiers.

Mechanism and efficacy of virus inactivation by a microplasma UV lamp generating monochromatic UV irradiation at 222 nm

This study evaluated the potential of a microplasma UV lamp as an alternative UV source to the current mercury-based (Hg-based) UV lamp for water disinfection. We developed a set of PCR-based molecular assays (long-range qPCR, DNase, and binding assay) to quantify the adenovirus genome, capsid, and fiber damage with a wide detection range (10^0.5-10^6.5 PFU/mL). We used these molecular assays to characterize adenovirus (AdV) inactivation kinetics by microplasma UV that produced monochromatic UV at 222 nm. We found that the inactivation rate constant (0.142 cm²/mJ) due to microplasma UV was 4.4 times higher than that of low-pressure Hg UV (0.032 cm²/mJ). This high efficacy was attributed to monochromatic UV wavelength at 222 nm damaging the AdV capsid protein. The results of these molecular assays also proved that microplasma UV and medium-pressure Hg UV with a bandpass filter at 223 nm (MPUV_223nm) have a similar influence on AdV (p>0.05). We then estimated the relative energy efficiency of MPUV and microplasma UV to LPUV for 4 log reduction of the viruses. We found that the microplasma UV resulted in higher inactivation rate constants for viruses than the current Hg-based UV. Consequently, microplasma UV could be more energy efficient than low-pressure Hg UV for water disinfection if the wall-plug efficiency of the microplasma UV lamp improved to 8.4% (currently 1.5%). Therefore, the microplasma UV lamp is a promising option for water disinfection.

Quick assessment of influenza a virus infectivity with a long-range reverse-transcription quantitative polymerase chain reaction assay

BACKGROUND

The polymerase chain reaction (PCR) is commonly used to detect viral pathogens because of its high sensitivity and specificity. However, conventional PCR methods cannot determine virus infectivity. Virus infectivity is conventionally examined with methods such as the plaque assay, even though such assays require several days. Long-range reverse-transcription quantitative PCR (RT-qPCR) has previously been suggested for the rapid assessment of RNA virus infectivity where the loss of infectivity is attributable to genomic fragmentation.

METHODS

IAV was irradiated with 253.7 nm ultraviolet (UV) rays to induce genomic strand breaks that were confirmed by a full-length RT-PCR assay. The IAV was then subjected to plaque assay, conventional RT-qPCR and long-range RT-qPCR to examine the relationship between infectious titer and copy number. A simple linear regression analysis was performed to examine the correlation between the results of these assays.

RESULTS

A long-range RT-qPCR assay was developed and validated for influenza A virus (IAV). Although only a few minutes of UV irradiation was required to completely inactivate IAV, genomic RNA remained detectable by the conventional RT-qPCR and the full-length RT-PCR for NS of viral genome following inactivation. A long-range RT-qPCR assay was then designed using RT-priming at the 3' termini of each genomic segment and subsequent qPCR of the 5' regions. UV-mediated IAV inactivation was successfully analyzed by the long-range RT-qPCR assay especially when targeting PA of the viral genome. This was also supported by the regression analysis that the long-range RT-qPCR is highly correlated with plaque assay (Adjusted R² = 0.931, P = 0.000066).

CONCLUSIONS

This study suggests that IAV infectivity can be predicted without the infectivity assays. The rapid detection of pathogenic IAV has, therefore, been achieved with this sensing technology.

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.

Measuring radiation-induced DNA damage in Cryptococcus neoformans and Saccharomyces cerevisiae using long range quantitative PCR

DNA damage has been considered to be the universal critical lesion in cells after exposure to ionizing radiation. Measuring radiation-induced DNA damage is important to understand the mechanisms of radiation-induced toxicity and monitor DNA damage repairs. Currently the most widely used methods to measure DNA damage are pulsed-field gel electrophoresis (PFGF) and single-cell gel electrophoresis (also known as the comet assay), both of which are technically challenging and time consuming. Long range quantitative polymerase chain reaction (LR-QPCR) has been used successfully to measure nuclear and mitochondrial DNA damage in mammalian and several model organism cells. The principle of this assay is that DNA lesions will slow down or block the progression of DNA polymerase. Therefore, the amplification efficiency of DNA with fewer lesions will be higher than DNA with more lesions under the same reaction condition. Here, we developed the LR-QPCR assay primers and reaction conditions to quantify DNA damage in Cryptococcus neoformans (C. neoformans) and Saccharomyces cerevisiae (S. cerevisiae) after gamma ray exposure. Under these conditions, long DNA targets of C. neoformans H99 and S. cerevisiae BY4741 (17.6 and 16.4 kb for nuclear DNA and 15.3 and 14.6 kb for mitochondrial DNA) were quantitatively amplified using extracted DNA templates, respectively. Two short mitochondrial DNA targets of these two species (207 bp and 154 bp) were also quantitatively amplified and used to monitor the number of mitochondria. Using the LR-QPCR method, we showed that the frequency of radiation-induced mitochondrial and nuclear DNA lesions had a significant linear correlation with the radiation doses (from 500 Gy to 3000 Gy) in both species. Furthermore, the faster disappearance of DNA damage detected in C. neoformans H99S strain compared to H99 strain may help to explain the different radiation sensitivity of these two strains. In summary, we developed a simple, sensitive method to measure radiation-induced DNA damage, which can greatly facilitate the study of radiation-induced toxicity and can be widely used as a dosimetry in radiation-induced cell damage.

Adenovirus Replication Cycle Disruption from Exposure to Polychromatic Ultraviolet Irradiation

Polychromatic ultraviolet (UV) light with bandwidth of 20 nm and peak emission centered at 224, 254, or 280 nm (UV₂₂₄, UV₂₅₄, and UV₂₈₀, respectively) were used to inactivate human adenovirus type 2 (HAdV-2). Quantitative polymerase chain reaction (qPCR) and reverse transcriptase qPCR assays were used to elucidate the step in the HAdV-2 replication cycle that was disrupted after UV exposure. UV treatment at any of the wavelengths analyzed did not inhibit association of HAdV-2 to the host cells even after exposure to a fluence (UV dose) that would produce a virus inactivation efficiency, measured by plaque assay, greater than 99.99%. In contrast, UV irradiation at all three peak emissions disrupted early E1A gene transcription and viral DNA replication, but different mechanisms appeared to be dominating such disruptions. UV₂₂₄ seemed to have little effect on the integrity of the viral genome but produced a structural transformation of the viral capsid that may inhibit the delivery of viral genome into the host cell nucleus. On the other hand, UV₂₅₄ and UV₂₈₀ did not affect the integrity of the viral capsid, but the mutations they produced on the viral genome might cause the inhibition of the early gene transcription and DNA replication after the viral genome successfully translocated into the host cell nucleus.

Mechanisms of ultraviolet disinfection and chlorination of Escherichia coli: Culturability, membrane permeability, metabolism, and genetic damage

Traditional culture methods may underestimate the tolerance of microorganisms to disinfectants because of the existence of viable but nonculturable or sublethally injured cells after disinfection. The selection of a strict method is crucial for the evaluation of disinfection performance. The actions of 2 typical disinfectants - ultraviolet (UV) and chlorine - on the fecal indicator Escherichia coli were investigated by the detection of culturability, membrane permeability, metabolic activity, deoxyribonucleic acid (DNA), and messenger ribonucleic acid (mRNA). During UV disinfection, the irreversible damages in the cell membrane and cellular adenosine triphosphate (ATP) were negligible at low UV doses (<80mJ/cm²). However, membrane permeability was damaged at low doses of chlorine (<5mg/L), leading to leakage of cellular ATP. Our study showed that a slight lesion in DNA was detected even at high doses of UV (400mJ/cm²) and chlorine (>5mg/L) treatments. The decay of mRNA was more rapid than that of DNA. The degradation level of mRNA depended on the choice of target genes. After exposure to 50mJ/cm² UV dose or 5mg/L chlorine for 30min, the DNA damage repair function (RecA mRNA) was inhibited. The mRNA involved in the DNA damage repair function can be a potential indicator of bacterial viability.

Wavelength-Dependent Damage to Adenoviral Proteins Across the Germicidal UV Spectrum

Adenovirus, a waterborne pathogen responsible for causing bronchitis, pneumonia, and gastrointestinal infections, is highly resistant to UV disinfection and therefore drives the virus disinfection regulations set by the U.S. Environmental Protection Agency. Polychromatic UV irradiation has been shown to be more effective at inactivating adenovirus and other viruses than traditional monochromatic irradiation emitted at 254 nm; the enhanced efficacy has been attributed to UV-induced damage to viral proteins. This research shows UV-induced damage to adenoviral proteins across the germicidal UV spectrum at wavelength intervals between 200 and 300 nm. A deuterium lamp with bandpass filters and UV light-emitting diodes (UV LEDs) isolated wavelengths in approximate 10 nm intervals. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and image densitometry were used to detect signatures for the hexon, penton, fiber, minor capsid, and core proteins. The greatest loss of protein signature, indicating damage to viral proteins, occurred below 240 nm. Hexon and penton proteins exposed to a dose of 28 mJ/cm² emitted at 214 nm were approximately 4 times as sensitive and fiber proteins approximately 3 times as sensitive as those exposed to a dose of 50 mJ/cm² emitted at 254 nm. At 220 nm, a dose of 38 mJ/cm² reduced the hexon and penton protein quantities to approximately 33% and 31% of the original amounts, respectively. In contrast, a much higher dose of 400 mJ/cm² emitted at 261 and 278 nm reduced the original protein quantity to between 66-89% and 80-93%, respectively. No significant damage was seen with a dose of 400 mJ/cm² at 254 nm. This research directly correlates enhanced inactivation at low wavelengths with adenoviral protein damage at those wavelengths, adding fundamental insight into the mechanisms of inactivation of polychromatic germicidal UV irradiation for improving UV water disinfection.

Toward a better guard of coastal water safety-Microbial distribution in coastal water and their facile detection

Prosperous development in marine-based tourism has raised increasing concerns over the sanitary quality of coastal waters with potential microbial contamination. The World Health Organization has set stringent standards over a list of pathogenic microorganisms posing potential threats to people with frequent coastal water exposure and has asked for efficient detection procedures for pathogen facile identification. Inspection of survey events regarding the occurrence of marine pathogens in recreational beaches in recent years has reinforced the need for the development of a rapid identification procedure. In this review, we examine the possibility of recruiting uniform molecular assays to identify different marine pathogens and the feasibility of appropriate biomarkers, including enterochelin biosynthetic genes, for general toxicity assays. The focus is not only on bacterial pathogens but also on other groups of infectious pathogens. The ultimate goal is the development of a handy method to more efficiently and rapidly detect marine pathogens.

Quantitative reverse transcription PCR to determine the inactivation of Human Rotavirus by chlorine

Human rotaviruses (HRVs) are the major cause of acute diarrhea in infants and young children. Here, a real-time reverse transcription polymerase chain reaction assay targeting the rotaviral VP4 gene (VP4-RT-qPCR) was established to evaluate the inactivation of HRV upon chlorine disinfection, based on a previous report that damage to the 1227-2354bp region of the VP4 gene was associated with eliminated HRV infectivity by chlorine. In this study, inactivation of HRV by 0.6mg/L free chlorine was assessed in phosphate buffered saline (PBS; pH 7.2), and tap and river water samples, using both TCID₅₀ and RT-qPCR (VP2- and VP4-RT-qPCR) assays, respectively. Among the samples tested, the VP2-RT-qPCR method did not show significant inactivation after chlorine disinfection; however, the reduction in VP4-RT-qPCR signal was correlated with decreased HRV infectivity. Moreover, the higher sensitivity of the VP4-RT-qPCR assay allowed for assessment of chlorine HRV inactivation at longer exposure times compared with the conventional TCID₅₀ assay. Collectively, these results indicated that the VP4-RT-qPCR assay is a rapid, sensitive, and reliable tool to detect infectious HRV following chlorine inactivation, and highlights the potential for further development of qPCR/RT-qPCR assays to provide information regarding viral infectivity from drinking water plants.

Analysis of Hydroxyl Radicals and Inactivation Mechanisms of Bacteriophage MS2 in Response to a Simultaneous Application of UV and Chlorine

The simultaneous application of UV and chlorine (expressed as UV/Cl₂) as a water treatment method may be a good disinfection option for UV-resistant microorganisms, such as human adenoviruses (HAdVs). In this study, we developed two approaches using UV/Cl₂: one to quantitate the OH• radicals based on the degradation of the probe compound para-chlorobenzoic acid (pCBA) and the other to use bacteriophage MS2 to understand the virus inactivation mechanisms in response to UV, chlorine and UV/Cl₂ disinfection using reverse-transcription quantitative polymerase chain reaction (RT-qPCR), attachment and genome penetration assays. The results revealed that OH• radicals were produced at a concentration of 2.70 × 10^-14 M in the UV/Cl₂ treatment with a practical chlorine dose of 1 mg/L and with a minimum UV₂₅₄ fluence of approximately 10 mJ/cm², whereas UV or chlorine alone did not produce OH• radicals. In the UV/Cl₂ treatment, synergistic effects on viral genome damage were observed, but were not directly due to OH• radicals. The ability of MS2 to penetrate the genome of the host bacteria was impaired, but its ability to attach to the host was not affected by the treatment. We concluded that the major cause of virus inactivation in response to UV/Cl₂ was the damage to the viral genome caused by combination actions of chlorine species and OH• radicals.

Technical aspects of using human adenovirus as a viral water quality indicator

Despite dramatic improvements in water treatment technologies in developed countries, waterborne viruses are still associated with many of cases of illness each year. These illnesses include gastroenteritis, meningitis, encephalitis, and respiratory infections. Importantly, outbreaks of viral disease from waters deemed compliant from bacterial indicator testing still occur, which highlights the need to monitor the virological quality of water. Human adenoviruses are often used as a viral indicator of water quality (faecal contamination), as this pathogen has high UV-resistance and is prevalent in untreated domestic wastewater all year round, unlike enteroviruses and noroviruses that are often only detected in certain seasons. Standard methods for recovering and measuring adenovirus numbers in water are lacking, and there are many variations in published methods. Since viral numbers are likely under-estimated when optimal methods are not used, a comprehensive review of these methods is both timely and important. This review critically evaluates how estimates of adenovirus numbers in water are impacted by technical manipulations, such as during adenovirus concentration and detection (including culturing and polymerase-chain reaction). An understanding of the implications of these issues is fundamental to obtaining reliable estimation of adenovirus numbers in water. Reliable estimation of HAdV numbers is critical to enable improved monitoring of the efficacy of water treatment processes, accurate quantitative microbial risk assessment, and to ensure microbiological safety of water.

Viral persistence in surface and drinking water: Suitability of PCR pre-treatment with intercalating dyes

After many outbreaks of enteric virus associated with consumption of drinking water, the study of enteric viruses in water has increased significantly in recent years. In order to better understand the dynamics of enteric viruses in environmental water and the associated viral risk, it is necessary to estimate viral persistence in different conditions. In this study, two representative models of human enteric viruses, adenovirus 41 (AdV 41) and coxsackievirus B2 (CV-B2), were used to evaluate the persistence of enteric viruses in environmental water. The persistence of infectious particles, encapsidated genomes and free nucleic acids of AdV 41 and CV-B2 was evaluated in drinking water and surface water at different temperatures (4 °C, 20 °C and 37 °C). The infectivity of AdV 41 and CV-B2 persisted for at least 25 days, whatever the water temperature, and for more than 70 days at 4 °C and 20 °C, in both drinking and surface water. Encapsidated genomes persisted beyond 70 days, whatever the water temperature. Free nucleic acids (i.e. without capsid) also were able to persist for at least 16 days in drinking and surface water. The usefulness of a detection method based on an intercalating dye pre-treatment, which specifically targets preserved particles, was investigated for the discrimination of free and encapsidated genomes and it was compared to virus infectivity. Further, the resistance of AdV 41 and CV-B2 against two major disinfection treatments applied in drinking water plants (UV and chlorination) was evaluated. Even after the application of UV rays and chlorine at high doses (400 mJ/cm(2) and 10 mg.min/L, respectively), viral genomes were still detected with molecular biology methods. Although the intercalating dye pre-treatment had little use for the detection of the effects of UV treatment, it was useful in the case of treatment by chlorination and less than 1 log10 difference in the results was found as compared to the infectivity measurements. Finally, for the first time, the suitability of intercalating dye pre-treatment for the estimation of the quality of the water produced by treatment plants was demonstrated using samples from four drinking-water plants and two rivers. Although 55% (27/49) of drinking water samples were positive for enteric viruses using molecular detection, none of the samples were positive when the intercalating dye pre-treatment method was used. This could indicate that the viruses that were detected are not infectious.

Molecular Methods for Assessment of Antibiotic Resistance in Agricultural Ecosystems: Prospects and Challenges

Agricultural ecosystems are of special interest for monitoring the potential for antibiotic resistance to spread through the environment and contribute to human exposure. Molecular methods, which target DNA, RNA, and other molecular components of bacterial cells, present certain advantages for characterizing and quantifying markers of antibiotic resistance and their horizontal gene transfer. These include rapid, unambiguous detection of targets; consistent results; and avoidance of culture bias. However, molecular methods are also subject to limitations that are not always clearly addressed or taken into consideration in the interpretation of scientific data. In particular, DNA-based methods do not directly assess viability or presence within an intact bacterial host, but such information may be inferred based on appropriate experimental design or in concert with complementary methods. The purpose of this review is to provide an overview of existing molecular methods for tracking antibiotic resistance in agricultural ecosystems, to define their strengths and weaknesses, and to recommend a path forward for future applications of molecular methods and standardized reporting in the literature. This will guide research along the farm-to-fork continuum and support comparability of the growing number of studies in the literature in a manner that informs management decisions and policy development.

Evaluation of three full-scale stormwater treatment systems with respect to water yield, pathogen removal efficacy and human health risk from faecal pathogens

In this study, three full-scale, operational stormwater harvesting systems located in Melbourne, Australia were evaluated with respect to water yields; pathogen removal performance by analysis of native surrogate data (Escherichiacoli, somatic coliphages and Clostridium perfringens); and potential human health risk associated with exposures to faecal pathogens using Quantitative Microbial Risk Assessment (QMRA). The water yield assessment confirmed variation between design and measured yields. Faecal contamination of urban stormwater was site specific and variable. Different treatment removal performance was observed between each of the microbial surrogates and varied between event and baseline conditions, with negligible removal of viruses during event conditions. Open storages that provide a habitat for waterfowl may lead to elevated risk due to the potential for zoonotic transmission. Nevertheless, in the Australian urban setting studied, the potential for human faecal contamination of the separated stormwater system was a critical driver of risk. If the integrity of the sewerage system can be ensured, then predicted health risks are dramatically reduced.

Global and local health burden trade-off through the hybridisation of quantitative microbial risk assessment and life cycle assessment to aid water management

Life cycle assessment (LCA) and quantitative risk assessment (QRA) are commonly used to evaluate potential human health impacts associated with proposed or existing infrastructure and products. Each approach has a distinct objective and, consequently, their conclusions may be inconsistent or contradictory. It is proposed that the integration of elements of QRA and LCA may provide a more holistic approach to health impact assessment. Here we examine the possibility of merging LCA assessed human health impacts with quantitative microbial risk assessment (QMRA) for waterborne pathogen impacts, expressed with the common health metric, disability adjusted life years (DALYs). The example of a recent large-scale water recycling project in Sydney, Australia was used to identify and demonstrate the potential advantages and current limitations of this approach. A comparative analysis of two scenarios - with and without the development of this project - was undertaken for this purpose. LCA and QMRA were carried out independently for the two scenarios to compare human health impacts, as measured by DALYs lost per year. LCA results suggested that construction of the project would lead to an increased number of DALYs lost per year, while estimated disease burden resulting from microbial exposures indicated that it would result in the loss of fewer DALYs per year than the alternative scenario. By merging the results of the LCA and QMRA, we demonstrate the advantages in providing a more comprehensive assessment of human disease burden for the two scenarios, in particular, the importance of considering the results of both LCA and QRA in a comparative assessment of decision alternatives to avoid problem shifting. The application of DALYs as a common measure between the two approaches was found to be useful for this purpose.

Analysis of the viral replication cycle of adenovirus serotype 2 after inactivation by free chlorine

Free chlorine is effective at inactivating a wide range of waterborne viral pathogens including human adenovirus (HAdV), but the mechanisms by which free chlorine inactivates HAdV and other human viruses remain to be elucidated. Such advances in fundamental knowledge are key for development of new disinfection technologies and novel sensors to detect infectious viruses in drinking water. We developed and tested a quantitative assay to analyze several steps in the HAdV replication cycle upon increasing free chlorine exposure. We used quantitative polymerase chain reaction (qPCR) to detect HAdV genomic DNA as a means to quantify attachment and genome replication of untreated and treated virions. Also, we used quantitative reverse-transcription PCR (RT-qPCR) to quantify the transcription of E1A (first early protein) and hexon mRNA. We compared these replication cycle events to virus inactivation kinetics to determine what stage of the virus replication cycle was inhibited as a function of free chlorine exposure. We observed that adenovirus inactivated at levels up to 99.99% by free chlorine still attached to host cells; however, viral DNA synthesis and early E1A and late hexon gene transcription were inhibited. We conclude that free chlorine exposure interferes with a replication cycle event occurring postbinding but prior to early viral protein synthesis.

Photovoltaic powered ultraviolet and visible light-emitting diodes for sustainable point-of-use disinfection of drinking waters

For many decades, populations in rural and remote developing regions will be unable to access centralised piped potable water supplies, and indeed, decentralised options may be more sustainable. Accordingly, improved household point-of-use (POU) disinfection technologies are urgently needed. Compared to alternatives, ultraviolet (UV) light disinfection is very attractive because of its efficacy against all pathogen groups and minimal operational consumables. Though mercury arc lamp technology is very efficient, it requires frequent lamp replacement, involves a toxic heavy metal, and their quartz envelopes and sleeves are expensive, fragile and require regular cleaning. An emerging alternative is semiconductor-based units where UV light emitting diodes (UV-LEDs) are powered by photovoltaics (PV). Our review charts the development of these two technologies, their current status, and challenges to their integration and POU application. It explores the themes of UV-C-LEDs, non-UV-C LED technology (e.g. UV-A, visible light, Advanced Oxidation), PV power supplies, PV/LED integration and POU suitability. While UV-C LED technology should mature in the next 10 years, research is also needed to address other unresolved barriers to in situ application as well as emerging research opportunities especially UV-A, photocatalyst/photosensitiser use and pulsed emission options.

Evaluation of DNA damage reversal during medium-pressure UV disinfection

Ultraviolet (UV) disinfection relies on the principal that DNA exposure to UV irradiation leads to the formation of cytotoxic lesions resulting in the inactivation of microorganisms. Cyclobutane pyrimdine dimers (CPDs) account for the majority of DNA lesions upon UV exposure. Past research has demonstrated reversal of CPDs in extracted DNA formed at high UV-C wavelength irradiation (280 nm) upon subsequent irradiation at lower UVC wavelengths (230-240 nm). Medium-pressure (MP) UV lamps produce a polychromatic emission giving rise to the possibility that cellular DNA in a target pathogen may undergo simultaneous damage and repair when exposed to multiple wavelengths during the disinfection process, decreasing the efficiency of MP UV lamp disinfection. Culture techniques and a quantitative polymerase chain reaction (qPCR) assay were used to examine cell viability and DNA damage reversal. qPCR results indicated direct photoreversal of UV-induced DNA damage through sequential irradiations of 280 nm followed by 228 nm in Escherichia coli DNA. However, significant photoreversal was only observed after high initial doses and secondary doses of UV light. The doses where significant photoreversal took place were more than 10 times higher than those typically used in UV disinfection. Despite evidence of CPD photoreversal, bacterial growth assays showed no indication that sequential-wavelength irradiations result in higher survival rates than single-wavelength irradiations.

Photoreactivation of bacteriophages after UV disinfection: role of genome structure and impacts of UV source

The UV inactivation kinetics of bacteriophages MS2, PhiX174, T1 and PRD1 and the potential of bacterial UV repair mechanisms to reactivate these bacteriophages is described here. The selected bacteriophages represent a range of genome size, single and double stranded genomes, circular and linear organization and RNA and DNA. Bacteriophages were exposed to UV irradiation from two different collimated beam UV irradiation sources (medium-pressure (MP) mercury lamps and low-pressure (LP) mercury lamps) and assayed during which host-phage cultures were exposed to photoreactivating light for 6 h, then incubated overnight at 37 °C in the dark. Dark controls following UV exposure were performed in parallel. UV inactivation kinetics (using dark controls) showed that circular ssDNA phage (PhiX174) was the most sensitive and linear ssRNA phage (MS2) was the more resistant phage. No photoreactivation was observed for MS2 (RNA phage) and the highest photoreactivation was observed for PRD1. In the case of PRD1, the dose required for 4-log reduction (dark control) was around 35 mJ/cm(2), with a similar dose observed for both UV sources (MP and LP). When the photoreactivation step was added, the dose required for 4-log reduction using LP lamps was 103 mJ/cm(2) and for MP lamps was 60 mJ/cm(2). Genome organization differences between bacteriophages play an important role in resistance to UV inactivation and potential photoreactivation mediated by bacterial host mechanisms. The use of photoreactivation during the assay of PRD1 creates a more conservative surrogate for potential use in UV challenge testing.

Wavelength dependent UV inactivation and DNA damage of adenovirus as measured by cell culture infectivity and long range quantitative PCR

Adenovirus is regarded as the most resistant pathogen to ultraviolet (UV) disinfection due to its demonstrated resistance to monochromatic, low-pressure (LP) UV irradiation at 254 nm. This resistance has resulted in high UV dose requirements for all viruses in regulations set by the United States Environmental Protection Agency. Polychromatic, medium-pressure (MP) UV irradiation has been shown to be much more effective than 254 nm, although the mechanisms of polychromatic UV inactivation are not completely understood. This research analyzes the wavelength-specific effects of UV light on adenovirus type 2 by analyzing in parallel the reduction in viral infectivity and damage to the viral genome. A tunable laser from the National Institute of Standards and Technology was used to isolate single UV wavelengths. Cell culture infectivity and PCR were employed to quantify the adenoviral inactivation rates using narrow bands of irradiation (<1 nm) at 10 nm intervals between 210 and 290 nm. The inactivation rate corresponding to adenoviral genome damage matched the inactivation rate of adenovirus infectivity at 253.7 nm, 270 nm, 280 nm, and 290 nm, suggesting that damage to the viral DNA was primarily responsible for loss of infectivity at those wavelengths. At 260 nm, more damage to the nucleic acid was observed than reduction in viral infectivity. At 240 nm and below, the reduction of viral infectivity was significantly greater than the reduction of DNA amplification, suggesting that UV damage to a viral component other than DNA contributed to the loss of infectivity at those wavelengths. Inactivation rates were used to develop a detailed spectral sensitivity or action spectrum of adenovirus 2. This research has significant implications for the water treatment industry with regard to polychromatic inactivation of viruses and the development of novel wavelength-specific UV disinfection technologies.