Reduction of interfering cytotoxicity associated with wastewater sludge concentrates assayed for indigenous enteric viruses

Assessing infectivity of emerging enveloped viruses in wastewater and sewage sludge: Relevance and procedures

The emergence of SARS-CoV-2 has heightened the need to evaluate the detection of enveloped viruses in the environment, particularly in wastewater, within the context of wastewater-based epidemiology. The studies published over the past 80 years focused primarily on non-enveloped viruses due to their ability to survive longer in environmental matrices such as wastewater or sludge compared to enveloped viruses. However, different enveloped viruses survive in the environment for different lengths of time. Therefore, it is crucial to be prepared to assess the potential infectious risk that may arise from future emerging enveloped viruses. This will require appropriate tools, notably suitable viral concentration methods that do not compromise virus infectivity. This review has a dual purpose: first, to gather all the available literature on the survival of infectious enveloped viruses, specifically at different pH and temperature conditions, and in contact with detergents; second, to select suitable concentration methods for evaluating the infectivity of these viruses in wastewater and sludge. The methodology used in this data collection review followed the systematic approach outlined in the PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis) guidelines. Concentration methods cited in the data gathered are more tailored towards detecting the enveloped viruses' genome. There is a lack of suitable methods for detecting infectious enveloped viruses in wastewater and sludge. Ultrafiltration, ultracentrifugation, and polyethylene glycol precipitation methods, under specific/defined conditions, appear to be relevant approaches. Further studies are necessary to validate reliable concentration methods for detecting infectious enveloped viruses. The choice of culture system is also crucial for detection sensitivity. The data also show that the survival of infectious enveloped viruses, though lower than that of non-enveloped ones, may enable environmental transmission. Experimental data on a wide range of enveloped viruses is required due to the variability in virus persistence in the environment.

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.

Occurrence and levels of phages proposed as surrogate indicators of enteric viruses in different types of sludges

A method based on the treatment of sludge with beef extract recovered, with similar efficiency, the three groups of bacteriophages studied from different kinds of sludges. The three groups of bacteriophages were found in high numbers in the different sludge types, the highest value being that of somatic coliphages in primary sludge of a biological treatment plant (1.1 x 10(5) pfu g-1) and the lowest being that of Bacteroides fragilis phages (110 pfu g-1) in de-watered, anaerobically, mesophilically-digested sludge. All phages studied accumulated in the sludges. In primary and activated sludges, all three types accumulated similarly but in lime-treated sludge and de-watered, anaerobically, mesophilically-digested sludge, the relative proportion of F-specific bacteriophages decreased significantly with respect to somatic coliphages and bacteriophages infecting B. fragilis. All phages survived successfully in stored sludge, depending on the temperature, and again, F-specific bacteriophages survived less successfully than the others.

Processing procedures for recovering enteric viruses from wastewater sludges

A powdered beef extract specially formulated for recovering viruses from environmental samples and designated as beef extract V was evaluated using indigenous and viral seeded wastewater sludge samples. When beef extract V was used to process activated and aerobically digested sludge solids, virus recoveries were shown to be similar to other methods that used commercially available supplemented beef extract. When used to process other sludge solids (primary and activated without primary clarification), cytotoxicity resulted in the BGM cell line used for virus assay. When these sludge solids were processed with the supplemented commercially marketed beef extract cell toxicity did not occur. Metal concentrations in the processed sewage sludge eluates were analyzed, but based on the levels observed they could not be shown as the source of the cytotoxicity. This did not exclude possible synergistic cytotoxic effects or organometal complexes. The commercially marketed beef extract was supplemented with either a floccing aid (FeCl3), a filter aid (Celite) or a floc prepared from paste beef extract. The paste beef floc supplement proved to be the most useful and reliable method for processing for viruses from wastewater sludge solids.

Detecting Viruses in Water

Various and divergent approaches that have been used to concentrate and assay viruses from tap water and environmental freshwaters are summarized and briefly explained. The basic principles behind the different methodologies and descriptions of the most recent developments are emphasized. Comparisons help demonstrate the relative sensitivities of different concentration and assay techniques.

Comparison of cytopathogenicity, immunofluorescence and In situ DNA hybridization as methods for the detection of adenoviruses

Three different methods were compared for their efficiency at detection of adenoviruses. The samples examined for viral analysis consisted of concentrates prepared from raw sewage, chosen as providing a representation of the spectrum of viruses being intestinally shed from a large population at any given time. When using one single cell line, HEp-2, the overall numbers of adenoviruses detected using cytopathogenicity and immunofluorescence were roughly equal. In situ hybridization was approx. 40% more sensitive than either of these other methods as determined by average virus titers for the different samples, and also proved to be better by means of a nonparametric comparison. The 293 cell line was approx. 5 times more sensitive for detecting adenoviruses by cytopathogenicity as compared with the HEp-2 cell line, but proved unsuitable in our hands for quantitatively detecting indigenous adenoviruses by immunofluorescence. The relative number of indigenous adenoviruses present in the sewage concentrates we examined was, on average, 94-fold greater than that of enteroviruses. Assay of enteroviruses was performed by plaque assay in the BGM cell line.

Suppression of viral replication by guanidine: a comparison of human adenoviruses and enteroviruses

A comparison was made between the relative sensitivities of laboratory strain human adenoviruses and enteroviruses, and recently isolated human enteroviruses, to the presence of guanidine hydrochloride in cell culture media. The concentration of guanidine hydrochloride used was 100 micrograms per ml. Representatives of all six human Adenovirus subgenera were unaffected in their replication at this concentration of guanidine. The different human Enterovirus types examined varied in their sensitivity, with suppression ranging from less than 1 to 3 log10 units for laboratory strains, and from 2 to 7 log10 units for recently isolated viruses. The findings suggest a novel role for antiviral drugs; serving as an adjunct in facilitating selective isolation of specific virus groups which may be present as part of mixed viral populations.

A simple planimetric method to quantify cytotoxicity in cell culture monolayers

Planimetry was shown to be a rapid, simple and reproducible method to quantify gross cytotoxicity in cell culture monolayers. A shellfish extract prepared from blue mussels (Mytilus edulis) was cytotoxic to Buffalo green monkey kidney cells. Exposure of cells to mussel extracts for 1, 2 and greater than or equal to 4 h followed by agar (plaque assay) overlays produced 34, 87, and 100% destruction of the monolayers, respectively, within 72 h. Planigraphs, prepared from tracing areas of cytotoxicity onto sheets of paper, served as permanent records of toxicity which were easily measured by planimeter experienced and nonexperienced scientists. Planimetric procedures may have utility in measuring biological and chemical toxicity as well as physiological stress in cell monolayers.

Comparison of methods for rotavirus detection in water and results of a survey of Jerusalem wastewater

Methods for the detection of viable rotaviruses and rotavirus antigen in water were developed and compared. The methods included laboratory-developed enzyme-linked immunosorbent assays (ELISAs) with chromogenic and luminescent substrates, commercial Rotazyme and Enzygnost ELISAs, and an indirect immunofluorescent assay. Of the methods tested, the immunofluorescent assay and the Enzygnost ELISA were the most sensitive for the simian rotavirus SA-11. All of the methods were positive for human rotavirus from clinical specimens. Seeded SA-11 rotavirus was concentrated from water by absorption to and elution from Zeta Plus filters followed by organic flocculation. Interference with the assays by components of the wastewater concentrates was minimal for the ELISAs, although the undiluted organic flocs were cytotoxic for the immunofluorescent assay. A survey of Jerusalem wastewater was carried out over the course of 1 year, and samples were assayed for rotaviruses and enteroviruses. Although enteroviruses were found in almost all of the samples, all samples were negative for rotaviruses. The concentration of rotaviruses in the wastewater was thus below the detection limit of the method used.