Comparative sensitivity of various cell culture systems for isolation of viruses from wastewater and fecal samples

Use of Capsid Integrity-qPCR for Detecting Viral Capsid Integrity in Wastewater

Quantifying viruses in wastewater via RT-qPCR provides total genomic data but does not indicate the virus capsid integrity or the potential risk for human infection. Assessing virus capsid integrity in sewage is important for wastewater-based surveillance, since discharged effluent may pose a public health hazard. While integrity assays using cell cultures can provide this information, they require specialised laboratories and expertise. One solution to overcome this limitation is the use of photo-reactive monoazide dyes (e.g., propidium monoazide [PMAxx]) in a capsid integrity-RT-qPCR assay (ci-RT-qPCR). In this study, we tested the efficiency of PMAxx dye at 50 μM and 100 μM concentrations on live and heat-inactivated model viruses commonly detected in wastewater, including adenovirus (AdV), hepatitis A (HAV), influenza A virus (IAV), and norovirus GI (NoV GI). The 100 μM PMAxx dye concentration effectively differentiated live from heat-inactivated viruses for all targets in buffer solution. This method was then applied to wastewater samples (n = 19) for the detection of encapsulated AdV, enterovirus (EV), HAV, IAV, influenza B virus (IBV), NoV GI, NoV GII, and SARS-CoV-2. Samples were negative for AdV, HAV, IAV, and IBV but positive for EV, NoV GI, NoV GII, and SARS-CoV-2. In the PMAxx-treated samples, EV, NoV GI, and NoV GII showed -0.52-1.15, 0.9-1.51, and 0.31-1.69 log reductions in capsid integrity, indicating a high degree of potentially infectious virus in wastewater. In contrast, SARS-CoV-2 was only detected using RT-qPCR but not after PMAxx treatment, indicating the absence of encapsulated and potentially infectious virus. In conclusion, this study demonstrates the utility of PMAxx dyes to evaluate capsid integrity across a diverse range of viruses commonly monitored in wastewater.

Development of a Rapid Viability RT-PCR (RV-RT-PCR) Method to Detect Infectious SARS-CoV-2 from Swabs

Since the rapid onset of the COVID-19 pandemic, its causative virus, Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), continues to spread and increase the number of fatalities. To expedite studies on understanding potential surface transmission of the virus and to aid environmental epidemiological investigations, we developed a rapid viability reverse transcriptase PCR (RV-RT-PCR) method that detects viable (infectious) SARS-CoV-2 from swab samples in <1 day compared to several days required by current gold-standard cell-culture-based methods. The method integrates cell-culture-based viral enrichment in a 96-well plate format with gene-specific RT-PCR-based analysis before and after sample incubation to determine the cycle threshold (C_T) difference (ΔC_T). An algorithm based on ΔC_T ≥ 6 representing ∼ 2-log or more increase in SARS-CoV-2 RNA following enrichment determines the presence of infectious virus. The RV-RT-PCR method with 2-hr viral infection and 9-hr post-infection incubation periods includes ultrafiltration to concentrate virions, resulting in detection of <50 SARS-CoV-2 virions in swab samples in 17 hours (for a batch of 12 swabs), compared to days typically required by the cell-culture based method. The SARS-CoV-2 RV-RT-PCR method may also be useful in clinical sample analysis and antiviral drug testing, and could serve as a model for developing rapid methods for other viruses of concern.

Epidemical and etiological study on hand, foot and mouth disease following EV-A71 vaccination in Xiangyang, China

Coxsackievirus A6 (CV-A6) and Coxsackievirus A10 (CV-A10) have been emerging as the prevailing serotypes and overtaking Enterovirus A71 (EV-A71) and Coxsackievirus A16 (CV-A16) in most areas as main pathogens of hand, foot and mouth disease (HFMD) in China since 2013. To investigate whole etiological spectrum following EV-A71 vaccination of approximate 40,000 infants and young children in Xiangyang, enteroviruses were serotyped in 4415 HFMD cases from October 2016 to December 2017 using Real Time and conventional PCR and cell cultures. Of the typeable 3201 specimen, CV-A6 was the predominant serotype followed by CV-A16, CV-A10, CV-A5, CV-A2 and EV-A71 with proportions of 59.54%, 15.31%, 11.56%, 4.56%, 3.78% and 3.03%, respectively. Other 12 minor serotypes were also detected. The results demonstrated that six major serotypes of enteroviruses were co-circulating, including newly emerged CV-A2 and CV-A5. A dramatic decrease of EV-A71 cases was observed, whereas the total cases remained high. Multivalent vaccines against major serotypes are urgently needed for control of HFMD.

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.

Development of a new cell culture-based method and optimized protocol for the detection of enteric viruses

The development of rapid and effective methods to detect water- and food-borne enteric viruses is important for the prevention and control of mass infection. This study represents an attempt to develop a reliable cell culture-based detection system and optimize an effective and rapid protocol for the assaying of environmental samples for the presence of infectious enteric viruses. Six enteric viruses were used in this study: poliovirus, Coxsackie virus A9, Coxsackie virus B5, human rotavirus G1, hepatitis A virus, and adenovirus type 41. Among the cell lines from humans (A549, HeLa, HEK293, and HFF) and other primates (Vero, BS-C-1, FRhK-4, BGMK, and MA104), a cytopathic effect (CPE) analysis indicated that the MA104 cell line was the most optimal for use in the detection of infectious enteric viruses. Both the sensitivity and specificity of virus detection in MA104 cells were similar to or higher than those in standard BGMK cells. Next, a method was developed for the determination of the infectiousness of enteric viruses using the colorimetric thiazolyl blue (MTT) assay. This assay utilizes 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide to yield % values based on colorimetric results. These results were compared with those from a conventional CPE-based TCID(50) assay, revealing no statistically significant difference between the two methods. The MTT% values in MA104 cells were comparable to those in BGMK cells. This MA104 cell-based MTT assay could substitute for the classical BGMK cell-based CPE assay for infectious enteric viruses.

A comparative analysis of routine techniques: Reverse transcriptase polymerase chain reaction (RT-PCR) and five cell lines for detection of enteroviruses in stool specimens

BACKGROUND AND OBJECTIVES

Each year, Enteroviruses infect millions of people and cause different diseases. The agents are usually detected using cell culture. RD (Rhabdomyosarcoma) and L20B (L cells) are among the recommended cells by the World Health Organisation (WHO) for this purpose. Even though cell culture is the most common method used in diagnosing Enteroviruses in stool specimens, this particular method poses some problems, which include false positive or negative results, lack of a unique cell line for diagnosing all Enterovirus types in addition to being time consuming. For these reasons, an attempt was made to find better techniques of Enterovirus detection. RT-PCR (Reverse Transcriptase Polymerase Chain Reaction) is a technique used in place of the cell culture method. In this study, the cell culture method was compared with RT-PCR for detection of Enteroviruses in stool specimens.

MATERIAL AND METHOD

First, the chloroform treated stool samples were inoculated onto five cell lines, including RD, L20B, Hep-2 (Human Epidermoid carcinoma cell line), Vero (Verde Reno) and GMK (Green Monkey Kidney). The results were then compared with data from Enterovirus detection using the RT-PCR technique.

RESULTS AND CONCLUSION

The difference between RT-PCR and cell culture results was significant. Enteroviruses were detected in 24% of specimens using RT-PCR while cell lines could isolate Enteroviruses in just 14.4% of the samples.

Use of propidium monoazide in reverse transcriptase PCR to distinguish between infectious and noninfectious enteric viruses in water samples

Human enteric viruses can be present in untreated and inadequately treated drinking water. Molecular methods, such as the reverse transcriptase PCR (RT-PCR), can detect viral genomes in a few hours, but they cannot distinguish between infectious and noninfectious viruses. Since only infectious viruses are a public health concern, methods that not only are rapid but also provide information on the infectivity of viruses are of interest. The intercalating dye propidium monoazide (PMA) has been used for distinguishing between viable and nonviable bacteria with DNA genomes, but it has not been used to distinguish between infectious and noninfectious enteric viruses with RNA genomes. In this study, PMA in conjunction with RT-PCR (PMA-RT-PCR) was used to determine the infectivity of enteric RNA viruses in water. Coxsackievirus, poliovirus, echovirus, and Norwalk virus were rendered noninfectious or inactivated by treatment with heat (72 degrees C, 37 degrees C, and 19 degrees C) or hypochlorite. Infectious or native and noninfectious or inactivated viruses were treated with PMA. This was followed by RNA extraction and RT-PCR or quantitative RT-PCR (qRT-PCR) analysis. The PMA-RT-PCR results indicated that PMA treatment did not interfere with detection of infectious or native viruses but prevented detection of noninfectious or inactivated viruses that were rendered noninfectious or inactivated by treatment at 72 degrees C and 37 degrees C and by hypochlorite treatment. However, PMA-RT-PCR was unable to prevent detection of enteroviruses that were rendered noninfectious by treatment at 19 degrees C. After PMA treatment poliovirus that was rendered noninfectious by treatment at 37 degrees C was undetectable by qRT-PCR, but PMA treatment did not affect detection of Norwalk virus. PMA-RT-PCR was also shown to be effective for detecting infectious poliovirus in the presence of noninfectious virus and in an environmental matrix. We concluded that PMA can be used to differentiate between potentially infectious and noninfectious viruses under the conditions defined above.

Occurrence and distribution of culturable enteroviruses in wastewater and surface waters of north-eastern Spain

AIMS

Update information regarding occurrence and levels of culturable enteroviruses in several types of surface polluted waters in north-eastern Spain and determine the proportion of the different species and serotypes.

METHODS AND RESULTS

The best procedures on hand in our laboratory for concentrating and quantifying culturable enteroviruses from different water sample types were used. Sequencing was used for typing the virus isolates. Geometric means of enteroviruses densities expressed in plaque forming units per litre were 968 in raw sewage, 12.51 in secondary effluents, 0.017 in tertiary effluents, 0.4 in river water and 0.36 in seawater. Enterovirus densities in wastewater revealed certain seasonality with a maximum at the end of spring - beginning of the summer. Coxsackievirus B, and amid them serotype CB4, were the most abundant species and serotypes detected.

CONCLUSIONS

Densities of enteroviruses in different north-eastern Spain surface waters are similar to those present in industrialized countries with temperate climate. No wild polioviruses were detected. Distribution of species showed a clear prevalence of coxsackieviruses.

SIGNIFICANCE AND IMPACT OF THE STUDY

Information regarding enteroviruses in this geographical area provides valuable information to estimate the risk of enteroviruses transmission through water and for complementing clinical epidemiological data.

Comparison of multiple shell vial cell lines for isolation of enteroviruses: a national perspective

BACKGROUND

Isolation of enterovirus in cell culture is still utilized by clinical laboratories, for vaccine research, and for identifying serotypes for disease surveillance. Use of a combination of cell lines is recommended yet this practice has not been rigorously examined for shell vials.

OBJECTIVES

To evaluate the growth predilection of enterovirus serotypes for certain shell vial cell lines in clinical samples received at a national reference laboratory.

STUDY DESIGN

We retrospectively reviewed results of samples submitted for viral culture over a 3-year period. PMK, BGM, RD, A549, and MRC-5 cell lines grown in shell vials were inoculated and serotyped.

RESULTS

Of 55,816 cultures, 1047 (1.9%) yielded enterovirus representing 18 serotypes. Echovirus 7, echovirus 9, and echovirus 30 were the most common serotypes recovered in 2002, 2003, and 2004, respectively. PMK and MRC-5 recovered the majority of enterovirus isolates; the addition of BGM and RD cells increased our recovery rate by 13%. For 52.6% of enteroviral isolates, cytopathic effect was found in only a single cell line. PMK and BGM cells were effective in isolating coxsackieviruses, and RD and MRC-5 were useful particularly in isolating echoviruses.

CONCLUSIONS

A combination of shell vial cell lines is still recommended for recovery of enteroviruses.

Double-layer plaque assay for quantification of enteroviruses

We describe here a double-layer plaque assay for the quantification of enteroviruses, combining a monolayer plaque assay and a suspended-cell plaque assay. The double-layer assay provides significantly greater counts than other methods of virus quantification of both suspensions of pure culture viruses and naturally occurring viruses. The counts obtained by this method are approximately one order of magnitude greater than those obtained with the more commonly used method, the monolayer plaque assay. We conclude that the methods available for quantifying viruses rank in efficiency as follows: double-layer plaque assay >or=suspended-cell plaque assay > counting cytopathogenic virus adsorbed to cellulose nitrate membrane filters >or= most probable number of cytopathogenic units > monolayer plaque assay. Moreover, the double-layer plaque assay allows the use of two different cell lines in the two layers. Using the human colonic carcinoma cell line CaCo2 facilitates the recovery of a greater number and diversity of naturally occurring enteroviruses in water than the monolayer agar method. In addition, the pretreatment of cells with 5-iodo-2'-deoxyuridine (IDU) prior to the quantification of enteroviruses by the double-layer plaque assay provides significantly higher recoveries than the use of IDU does with the other methods of quantification.

Enterovirus isolation from children with acute respiratory infections and presumptive identification by a modified microplate method

OBJECTIVE

To evaluate a modified microplate method, utilizing HEF, HEp-2, Vero, MDCK and newly introduced RD-18S and GMK cell lines, for virus isolation.

METHODS

From June to October 2001, 723 throat swab specimens taken from children with acute respiratory infections (ARIs) were inoculated onto these cells. To analyze cell sensitivity, we also inoculated 20 serotypes of stocked enteroviruses.

RESULTS

During the period, we isolated 40 Coxsackie A2 (CoxA2), 13 CoxA4, 16 CoxA16, 1 CoxB2, 11 CoxB3, 2 CoxB5, 54 echo16, 2 entero71 and 1 polio2. By observing a cell sensitivity pattern with HEF, HEp-2, Vero, RD-18S, and GMK, we could finally differentiate five enterovirus groups: CoxA except for CoxA16, CoxA16/entero71, CoxB, echovirus, and poliovirus.

CONCLUSIONS

With this system, the RD-18S cell line enabled us to isolate CoxA virus, except for CoxA16, for the first time. Differentiation of five enterovirus groups by cell sensitivity simplified the specific identification by neutralization test as a presumptive identification. A modified microplate method may be an appropriate cell combination for virus isolation, especially for enteroviruses, and is expected to be used routinely for virologic diagnosis and to clarify the epidemiology of ARI in children.

Detection of enteroviruses in groundwater with the polymerase chain reaction

Standard methods for the detection of enteroviruses in environmental samples involve the use of cell culture, which is expensive and time-consuming. The polymerase chain reaction (PCR) is an attractive method for the detection of enteroviruses in water because primary cell culture is not needed and the increased sensitivity of PCR allows detection of the low numbers of target DNAs and RNAs usually found in environmental samples. However, environmental samples often contain substances that inhibit PCR amplification of target DNA and RNA. Procedures that remove substances that interfere with the amplification process need to be developed if PCR is to be successfully applied to environmental samples. An RNA-PCR assay for the detection of enteroviruses in water was developed and used to test a variety of groundwater concentrates and humic acid solutions seeded with poliovirus type 1. The groundwater samples and humic acid solutions were treated with Sephadex G-50, Sephadex G-100, Sephadex G-200, Chelex-100 resin, and a mixed bed resin to remove PCR-inhibitory material from the samples. Sephadex G-100 in combination with Chelex-100 was found to be very effective in removing inhibitory factors for the detection of enteroviruses in groundwater concentrates by PCR. Viruses were detected in two of the groundwater concentrates by the RNA-PCR assay after treatment with Sephadex G-100 plus Chelex-100. This was confirmed by tissue culture, suggesting that the treatment protocol and, subsequently, the RNA-PCR assay are applicable for the detection of enteroviruses in environmental samples.

Presumptive identification of enteroviruses with RD, HEp-2, and RMK cell lines

The limited supply of the Lim Benyesh-Melnick antiserum pools for the typing of enteroviruses has made this test inappropriate for routine use in most clinical laboratories. We studied the correlation between the enterovirus groups and the cell lines on which they displayed cytopathic effect in order to make identifications without using the neutralization test. This study indicated that a presumptive identification of the enterovirus group could be made on the basis of characteristic cytopathic effect displayed after passage into rhabdomyosarcoma (RD), HEp-2, and primary rhesus monkey kidney (RMK) cells. Echoviruses and group A coxsackieviruses could be isolated in RD and RMK cells but not HEp-2 cells. Group B coxsackievirus could be isolated in RMK and HEp-2 cells but not RD cells. Poliovirus could be isolated in all three cell lines. We recommend the use of these cell lines to make presumptive enterovirus group identifications for routine viral isolates.

Role of the virology laboratory in diagnosis and management of patients with central nervous system disease

A number of viruses cause acute central nervous system disease. The two major clinical presentations are aseptic meningitis and the less common meningoencephalitis. Clinical virology laboratories are now more widely available than a decade ago; they can be operated on a modest scale and can be tailored to the needs of the patients they serve. Most laboratories can provide diagnostic information on diseases caused by enteroviruses, herpesviruses, and human immunodeficiency virus. Antiviral therapy for herpes simplex virus is now available. By providing a rapid diagnostic test or isolation of the virus or both, the virology laboratory plays a direct role in guiding antiviral therapy for patients with herpes simplex encephalitis. Although there is no specific drug available for enteroviruses, attention needs to be paid to these viruses since they are the most common cause of nonbacterial meningitis and the most common pathogens causing hospitalization for suspected sepsis in young infants in the United States during the warm months of the year. When the virology laboratory maximizes the speed of viral detection or isolation, it can make a significant impact on management of these patients. Early viral diagnosis benefits patients with enteroviral meningitis, most of whom are hospitalized and treated for bacterial sepsis or meningitis or both; these patients have the advantage of early withdrawal of antibiotics and intravenous therapy, early hospital discharge, and avoidance of the risks and costs of unnecessary tests and treatment. Enteroviral infection in young infants also is a risk factor for possible long-term sequelae. For compromised patients, the diagnostic information helps in selecting specific immunoglobulin therapy. Good communication between the physician and the laboratory will result in the most benefit to patients with central nervous system viral infection.

Comparison of cell cultures for rapid isolation of enteroviruses

Cell culture isolation is still the most reliable method for the detection of enteroviruses from clinical specimens. Rapid diagnosis of enterovirus infection affects patient management. To increase yield and enhance the rapidity of enterovirus isolation in cell cultures, we used Buffalo green monkey kidney (BGM) cells and subpassages of primary human embryonic kidney (HEK) cells in addition to the human diploid fibroblast (MRC-5) cells and primary cynomolgus or rhesus monkey kidney (MK) cells routinely used for enterovirus culturing. Growth characteristics of enteroviruses from 421 specimens were studied. All specimens were cultured in MRC-5, MK, and BGM cells, and 204 of these specimens were also cultured in HEK cells. Forty-two percent of the enteroviruses became positive within 3 days, and 85% did so within 7 days. MRC-5 cells provided the highest yield of enteroviruses overall and were the best cell type for the recovery of poliovirus and echovirus. MK cells provided the second best yield but were more useful than MRC-5 cells for coxsackievirus. BGM cells supported the growth of additional isolates of coxsackievirus and enhanced the speed of isolation. HEK cells supported the growth of additional isolates of both coxsackievirus and echovirus, but subculturing was always required for definite enterovirus cytopathic effects. The recovery rate increased 11% when two additional cell lines were used. The use of two tubes of MK cells significantly increased the yield of all enterovirus types. We conclude that the use of multiple appropriate cell lines increases yield and enhances the rapidity of enterovirus isolation.

Animal viruses, coliphages, and bacteria in aerosols and wastewater at a spray irrigation site

Aerosol samples collected at the Muskegon County Wastewater Management System Number 1 spray irrigation site in Michigan by using the Army prototype XM2 Biological Sampler/Collector were examined for the presence of animal viruses, coliphages, and bacteria. Air samples, collected in Earle lactalbumen hydrolysate, and wastewater samples were filtered through a 0.45- and 1.2-micron membrane filter sandwich, pretreated with 10% beef extract (pH 7.0), and assayed for animal viruses by the plaque method on Buffalo green monkey kidney cells. Untreated air and wastewater samples were assayed for coliphages by the soft agar overlay method with three Escherichia coli hosts (ATCC 13706, 15597, and 11303) and for bacteria by the heterotrophic plate count method. Filtered air samples were assayed for coliphages by the most-probable-number method with the same three hosts. Although no animal viruses were detected in the aerosol samples, coliphages and bacteria were recovered. E. coli ATCC 13706 coliphage were recovered more often and in greater numbers than either of the other two types of coliphages. Concentrations of animal viruses, coliphages, and bacteria detected in the raw influent decreased as the wastewater was aerated and stored in the lagoons. No animal viruses were detected in the wastewater at the pump station just before distribution to the spray irrigation rigs. The most-probable-number method was more sensitive and consistent than the overlay procedure in detecting low levels of coliphages in air samples.

A combination of four cell types for rapid detection of enteroviruses in clinical specimens

Isolation in cell culture is currently the most sensitive and reliable way to demonstrate enterovirus (EV) in clinical specimens. During July-October 1982 and 1983, we studied the impact of adding two new cell lines, Buffalo green monkey kidney (BGM) and human rhabdomyosarcoma (RD), to the more traditional cell combination used for EV isolation, human embryonic lung (HEL) and primary cynomolgus monkey kidney (CMK) cells; 2,558 specimens were studied: 632 fecal, 677 respiratory, 537 CSF, and 712 blood. An EV was isolated from 417 (16%); of these, 77 (18%) were positive only in BGM or RD; 35% (146/417) of the specimens were positive in BGM, RD, or both, at least one day earlier than in the traditional cells. BGM cells were helpful in isolation of group B coxsackieviruses (CB): 99% of 121 positive specimens were detected in BGM vs 73% in CMK and 23% in HEL; 72% of the CB isolates were detected by day 2 in BGM vs 48% in CMK and 0% in HEL. RD cells were helpful in the isolation of echoviruses: 59% of the 189 positive specimens were detected in RD vs 67% in HEL and 58% in CMK. RD was the only positive cell type in 28/189 (15%) positive specimens; 31% of the echovirus isolates were detected by day 2 in RD, vs 20% in HEL and 19% in CMK. Using the cell types described, we provided the clinician with results in 42% of the EV-positive specimens by day 2 after inoculation and in 61% by day 4.

Optimization of the BGM cell line culture and viral assay procedures for monitoring viruses in the environment

An in-depth study of the continuous cell line designated BGM is described herein, and recommendations are made for standardizing cell culture and viral assay procedures. Based on data gathered from a survey of 58 laboratories using this cell line, a research plan was developed that included the study of growth media, sera, NaHCO3 levels, culture bottles, cell concentration, overlay media, agar, virus infection conditions, and cell-dissociating agents. Additionally, a comparative virus isolation study with BGM cells and nine other cell types was conducted with 37 sewage samples collected from nine different geographic areas. The results of the study indicated that the BGM cell line is superior for virus isolation when compared with the other cell types and that certain media and additives tend to increase BGM cell sensitivity to a specific group of viruses. A standardized procedure for cultivation of BGM cells is described which provides a more effective enterovirus assay system.

A comparison of the susceptibility of three human gut tumour-derived differentiated epithelial cell lines, primary monkey kidney cells and human rhabdomyosarcoma cell line to 66-prototype strains of human enteroviruses

The growth of prototype strains of 31 serotypes of ECHO, 3 polio, 6 Coxsackie B, 24 Coxsackie A and enterovirus serotypes 70 and 71 were tested in parallel in primary monkey kidney cells (PMK), RD cells and three gut tumour-derived differentiated epithelial cell lines (HRT-18 HT-29 in SKCO-1). All 31 serotypes of ECHO viruses grew in HT-29, 27 and SKCO-1, 5 in HRT-18, 29 in PMK and 29 in RD. There was good growth of poliovirus serotypes in all five cell types. Coxsackie B viruses grew well in all the cell lines except RD. Fifteen of the Coxsackie A viruses grew in SKCO-1, 4 in HT-29, 3 in HRT-18 and 7 in RD. Enterovirus serotypes 70 and 71 grew only in RD cells after 3 serial passages. These results showed that 2 of the gut tumour-derived cell lines, HT-29 and SKCO-1 had a markedly wider susceptibility, with comparable or wider sensitivity, for enteroviruses, than PMK and RD. While their use for field isolation from clinical samples is not yet fully established HT-29 and SKCO-1 would appear to be ideal for a variety of laboratory manipulations of the majority of enteroviruses.

Enteroviruses in sludge: multiyear experience with four wastewater treatment plants

We describe our experience with the isolation of viruses from four treatment plants located in different geographic areas. Over a period of 3 years, 297 enteroviruses were isolated from 307 sludge samples. The highest frequency of viral isolation (92%), including multiple isolates from single samples, was obtained from a treatment plant serving the smallest population. Excluding the polioviruses, 22 different enterovirus serotypes were isolated. The methods used to isolate the viruses were relatively simple and included an elution procedure in which beef extract was used and a disinfection step. No concentration procedure was used. Of three cell culture systems used, the RD line of human rhabdomyosarcoma cells was by far the most useful for the isolation of echoviruses; BGM and HeLa cells were particularly useful for the isolation of group B coxsackieviruses. A seasonal effect on viral isolation rates from sludge was observed.

Comparison of microporous filters for concentration of viruses from wastewater

The 1-MDS Virosorb filter and the 50S and 30S Zeta-plus filters, all with a net positive charge, were compared with the negatively charged Filterite filter for concentration of naturally occurring coliphages and animal viruses from sewage effluent. When Filterite filters were used, the effluent was adjusted to pH 3.5 and AlCl3 was added before filtration to facilitate virus adsorption. No adjustment was required with the positively charged filters. Sets of each filter type were eluted with 3% beef extract (pH 9.5) or eluted with 0.05 M glycine (pH 11.5). A maximum volume of 19 liters could be passed through 142-mm diameter Filterite filters before clogging, whereas only 11, 11, and 15 liters could be passed through the 1-MDS, 50S, and 30S filters, respectively. For equal volumes passed through the filters, coliphage recoveries were 14, 15, 18, and 37% in primary effluent and 40, 97, 50, and 46% in secondary effluent for the Filterite , 1-MDS, 50S, and 30S filters, respectively. No statistically significant difference was observed in the recovery of animal viruses among the filters from secondary effluent, whereas in the Filterite and 50S filters, higher numbers of viruses from primary effluent were recovered than in the 1-MDS and 30S filters in two of three collections. Glycine was found to be a less-efficient eluent than beef extract in the recovery of naturally occurring viruses.

Trypsin-treated Ma-104: a sensitive cell line for isolating enteric viruses from environmental samples

During a 1-year survey of enteroviruses in wastewater samples from the Lorraine area, three widely used continuous monkey kidney cell lines were tested: BGM, Vero, and trypsin-treated Ma-104. Decontaminated samples from secondary wastewater treatment plants (influent or effluent) were directly inoculated onto cells, and viruses were revealed after two passages with a liquid medium technique. Out of the total percentage of positive isolates with the three systems (32.7) 24.7% were found with Ma-104, 14.1% with BGM, and only 1.7% with Vero cells. Poliovirus was recovered more frequently with Ma-104 (12.3%) than with BGM (1.7%). Reovirus (3.5%) and echovirus (1.7%) were only found with Ma-104 cells; however, BGM cells allowed the isolation of a few group B coxsackieviruses (5.9%). It must be pointed out that 7.0% of samples with an unconfirmed cytopathic effect were found with BGM against 3.4% found with Ma-104, but they did not have significant differences. Because of its large spectrum of sensitivity, easy maintenance, and resistance to toxic effects, trypsin-treated Ma-104 may be recommended in conjunction with other cell lines for the detection of viruses from environmental samples, especially with the use of a liquid method.

Development of a shaker culture of Buffalo green monkey kidney cells: potential use for detection of enteroviruses

Buffalo green monkey kidney cells were adapted to grow as shaker cultures. Replication of environmental and clinical isolates of poliovirus, coxsackievirus, and echovirus in these cultures was analyzed by plaque assay and compared with replication in Buffalo green monkey kidney cell monolayers and HEp-2 cell shaker cultures. Dose-response tests with various concentrations of Mahoney type 1 poliovirus indicated that Buffalo green monkey kidney cell shaker cultures could detect as little as 1 PFU in an inoculum of 0.2 ml. These data suggest that Buffalo green monkey kidney cell shaker cultures can be effectively used for the detection of small quantities of enteroviruses from environmental sources.

Increased Efficiency of Group B Coxsackievirus Isolation from Clinical Specimens by Use of BGM Cells

A continuous African green monkey kidney cell line, designated BGM, was compared with primary cynomolgus monkey kidney cells and human embryonic lung cells for efficiency of enterovirus isolation. A selective enhanced sensitivity of BGM cells both in terms of isolation rate and speed of isolation was found for group B coxsackieviruses but could not be demonstrated for a number of other nonpolio enteroviruses.

Induction of cytopathogenicity in mammalian cell lines challenged with culturable enteric viruses and its enhancement by 5-iododeoxyuridine

Cultures of 17 established cell lines were tested against 105 enteric virus types for capacity to support viral replication as indicated by cytopathogenic effect production. Enhancement of susceptibility by treatment of the cells with 5-iododeoxyuridine was evaluated in parallel with untreated cells. Cytopathogenic effect was produced in two or more cell lines by every virus tested except six strains of group A coxsackie virus. No cell line was found to be susceptible to these six virus types. In general, treatment with 5-iododeoxyuridine provided a more rapid onset of cytopathogenic effect in susceptible cells and in some instances resulted in refractory cells becoming permissive to viral replication. The use of 5-iododeoxyuridine allowed two human embryonic lines (HEL-299 and L-132), in combination, to be susceptible to all but the six group A coxsackie virus strains.

Evaluation of cell lines and immunofluorescence and plaque assay procedures for quantifying reoviruses in sewage

Twelve continuous cell lines were tested to determine their sensitivity to reovirus types 1, 2, and 3 isolated from sewage. Madin-Darby bovine kidney (MDBK), rhesus monkey kidney (LLC-MK2), and human embryonic intestinal (intestinal 407) cells were most sensitive, respectively. In a similar study, MDBK cells were more sensitive than LLC-MK2 and Buffalo green monkey kidney (BGM) cells to sewage-isolated, protamine-precipitated reoviruses which had not been serotyped and had no previous cell contact. Sewage-isolated, protamine-precipitated reoviruses were also used in conjunction with MDBK cells in a comparative evaluation of immunofluorescent cell count and plaque assay procedures. The immunofluorescence assay is more sensitive and more rapid than the plaque assay. Reoviruses in excess of 10(4)/liter of raw sewage were detected by the immunofluorescent cell count assay.

Techniques for virus detection in aquatic sediments

Laboratory experiments have been undertaken to study the adsorption-desorption of poliovirus to and from marine and freshwater sediments. It was observed that marine sediments retained 99% of added virus, whereas, freshwater sediments adsorbed approximately 40% of the added virus. Ten eluents were investigated for their ability to desorb viruses from a marine sediment. It was found that virus elution from the marine sediment was relatively low and ranged from less than 1% to 44%. Two eluents, urea-lysine and TCA-glycine at pH 9.0, were found to be the most efficient among the eluents tested. Viruses were more easily released from freshwater than from marine sediments. When urea-lysine, beef extract and purified casein were used as eluents, the overall virus recovery ranged from 8% to 22% for the marine sediment and from 23% to 59% for the freshwater sediments. The urea-lysine methods was used for the detection of indigenous enteroviruses in sediments from a closed shellfish bed. Enteroviruses were recovered with concentrations up to 708 TCID50/50 g of sediment.

Virus Removal by Disinfection of Effluents

The safe disposal of effluents can present a major problem to large urban communities because of their inevitable content of potentially pathogenic enteric viruses. At least one hundred types of virus may be present although many of these are difficult or even impossible to characterise under these conditions. Wastewater treatment does not greatly effect the survival of many enteric viruses and some survive well even after effluent disposal. The use of disinfectants for the inactivation of virus in effluent is practicable but requires careful manipulation in order to avoid the disemination of byproducts toxic to man or capable of interferring with the ecology of the receiving waters or soils. No one system is likely to be either universally acceptable because of the variable quality of effluents and much research remains to be done before guidelines can be recommended or established.

One-year survey of enteroviruses, adenoviruses, and reoviruses isolated from effluent at an activated-sludge purification plant

Samples of raw sewage, primary effluent, and secondary effluent from a large activated-sludge purification plant near Melbourne (Victoria, Australia) were collected every second week for 1 year. Viruses were detected in all secondary effluent samples and in six of seven samples obtained after final chlorination. Adenoviruses (85% reduction) and reoviruses (28% reduction) were removed less efficiently by this treatment process than were enteroviruses (93% reduction). In addition, 57 of 171 samples of effluent tested were positive for either adenoviruses or reoviruses, or both, when enteroviruses were not isolated. This clearly shows that the use of enteroviruses as sole indicators of viruses in water may miss up to one-third of instances of viral contamination. Enteroviruses and adenoviruses were isolated most frequently in HeLa-R cell cultures, whereas reoviruses were most often isolated in primary monkey kidney cells.

Coliphages as ecological indicators of enteroviruses in various water systems

The occurrence of coliphages and enteroviruses in a variety of water systems in Czechoslovakia was monitored for two years. Two host strains of Escherichia coli bacteria were used to test 1161 water samples for the presence of bacteriophages. These strains were polyvalent hosts for a broad spectrum of morphologically distinct coliphages, and their use thus gave quantitative data on the degree of viral pollution in any given water sample. Ninety-two water samples were tested in parallel for the presence of enteroviruses, by using a flocculation method to concentrate the viruses followed by isolation in cultures of a buffalo green monkey (BGM) kidney continuous cell line. The enterovirus and coliphage recovery rates showed similar differences when waters with different levels of pollution were compared. Seasonal fluctuations of both the coliphage and enterovirus (mostly poliovirus) levels in river water were demonstrated by statistical analysis of the data collected. The levels increased in the winter and sharply declined in the summer months as the river water temperature increased. Chemical pollution did not seem to influence the survival of either the coliphages or the enteroviruses in the observed rivers.

Antigenic comparisons of two new rotaviruses from rhesus monkeys

Two rotavirus strains isolated in cell culture from infant rhesus monkeys with diarrhea were closely related to SA 11 virus and to each other by plaque reduction neutralization tests. However, results of immune electron microscopy suggested possible antigenic differences between the two rhesus rotavirus strains.

Improved method and test strategy for recovery of enteric viruses from shellfish

An improved recovery method and testing strategy were devised for recovery of low numbers of enteric viruses from each of three commercially important shellfish species. Effective recovery of virus depended as much upon details of the test strategy adopted for use of the improved method with each species as on the method itself. The most important test details involved sample composition, pool size, and method of use of cell cultures. Recovery sensitivity measured permitted detection of 25 to 3 plaque-forming units of enteroviruses and 100 to 27 plaque-forming units of reovirus through their recovery in cell culture, with effectivenesses averaging 64 and 46%, respectively. Test samples prepared by the improved recovery method were virtually cytotoxicity free. Optimal recovery of virus on 45-cm2 cell culture monolayers was obtained with 1-ml inocula adsorbed for 2 h. The most effective recovery of virus from shellfish samples was made by a sequential adsorption procedure which allowed equal exposure of an entire sample to each of two or more cell cultures. Removal of nonviral contaminants from test samples by antibiotic treatment was preferable to the use of ether or membrane filtration procedures.

Procedure for the recovery of airborne human enteric viruses during spray irrigation of treated wastewater

Because of the relatively low number of indigenous enteric viruses recovered from secondary wastewater effluents, their presence in air (aerosols) as a result of wastewater spray irrigation requires extensive sampling. Methodology to allow the recovery of indigenous enteroviruses from aerosols generated at an operational wastewater irrigation site was tested under both laboratory and field conditions.

Bioaccumulation and depuration of enteroviruses by the soft-shelled clam, Mya arenaria

Low levels of feces-associated natural virus, simulating virus numbers estimated to exist in moderately polluted shellfish-growing waters, were used to evaluate the effectiveness of depuration as a virus depletion procedure in soft-shell clams. Depuration effectiveness depended upon the numbers of virus bioaccumulated and whether virus was solids associated. Virus uptake was greatest when viruses were solids associated and pollution levels were equivalent or greater than those likely to be found in grossly polluted growing waters. Virtually all bioaccumulated feces-associated natural virus was deposited within either the hepatopancreas or siphon tissues. Viruses usually were eliminated within a 24- to 48-h depuration period. Dependence upon depuration of clams to elimate health hazards of virus etiology involved a risk factor not measureable in the study. The greatest reduction of health risks would come from the routine depuration of clams harvested from growing waters of good sanitary quality.