Here we present VirWaTest, which is a simple, affordable and portable method for the concentration and detection of viruses from water samples at the point of use.
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Method Article
Here we present VirWaTest, which is a simple, affordable and portable method for the concentration and detection of viruses from water samples at the point of use.
Viruses excreted by humans and animals may contaminate water sources and pose a risk to human health when this water is used for drinking, food irrigation, washing, etc. The classical fecal bacteria indicator does not always check for the presence of viral pathogens so the detection of viral pathogens and viral indicators is relevant in order to adopt measures of risk mitigation, especially in humanitarian scenarios and in areas where water-borne viral outbreaks are frequent.
At present, several commercial tests allowing the quantification of fecal indicator bacteria (FIB) are available for testing at the point of use. However, such commercial tests are not available for the detection of viruses. The detection of viruses in environmental water samples requires concentrating several liters into smaller volumes. Moreover, once concentrated, the detection of viruses relies on methods such as nucleic acid extraction and molecular detection (e.g., polymerase chain reaction [PCR]-based assays) of the viral genomes.
The method described here allows the concentration of viruses from 10 L water samples, as well as the extraction of viral nucleic acids at the point of use, with simple and portable equipment. This allows the testing of water samples at the point of use for several viruses and is useful in humanitarian scenarios, as well as at any context where an equipped laboratory is not available. Alternatively, the method allows concentrating viruses present in water samples and the shipping of the concentrate to a laboratory at room temperature for further analysis.
During the first phases of any humanitarian emergency, access to clean water supplies, sanitation, and hygiene are critical for the survival of those affected. Therefore, monitoring water quality is a priority to prevent waterborne outbreaks. It is well-known that contaminated water is frequently the origin of diseases, but it is often difficult to determine the sources of viral outbreaks such as Hepatitis E virus (HEV), even with the availability of conventional laboratory methods. The control of water quality is based on the quantification of FIB1,2,3,4. However, it has been extensively documented that there is no correlation between the absence of FIB and the presence of viral waterborne pathogens such as rotavirus (RoV), norovirus (NoV), or HEV5,6. Thus, using the water quality criteria based on FIB might result in an underestimation of risks associated with the presence of waterborne viral pathogens. The surveillance of indicator viruses, such as human adenoviruses (HAdV), or specific pathogens would be helpful in defining the exposure to viral pathogens and identifying the potential source of human infection7,8,9,10 and in validating the efficacy of sanitation measures11.
Until now, the detection of viruses in these scenarios relied on skilled staff and complex logistics. VirWaTest (virwatest.org) is aimed at the development of a simple, affordable, and portable method for the concentration and subsequent detection of viruses from water samples at the point of use.
The virus concentration is based on the principle of organic flocculation of 10 L water samples, by which viruses are recovered in smaller volumes12,13. The flocs are collected and added to a buffer that lyses the viruses and prevents the nucleic acids from degradation when they stored at room temperature for not more than 2 weeks.
The nucleic acid extraction method is based on the use of magnetic particles to which the nucleic acids get adsorbed. They can be transferred from one washing buffer to another and finally into the elution buffer by using a magnetic pipette to which the particles attach. Viral nucleic acid suspensions obtained can be shipped to a reference laboratory where the detection can be performed using molecular methods based on PCR. For each nucleic acid extraction, two different quantities are tested to rule out enzymatic inhibition originated by the sample. Alternatively, with minimum equipment availability, PCR tests can be run at the point of use. The entire process is designed to be performed independently of a power supply (Figure 1).
A quantitative PCR assay to detect HAdV, excreted by humans and found in wastewater samples in high concentrations, has been adapted to be run at the point of use. HAdV are used as human fecal viral indicators. A PCR for the quantification of MS2 bacteriophage has been also adapted since MS2 is used in VirWaTest as process control. The method can be customized for the detection of any virus of interest.
After development, the VirWaTest method has been applied by the users in two different settings in the Republic of Central Africa (RCA) and Ecuador, providing feedback on the application of the protocol in real situations.
To our knowledge, this is the first procedure that allows the concentration and detection of viruses at the point of use, independent of any power supply, large equipment, and freezing/cooling conditions. It is recommended to collect two replicates of each water sample in order to obtain robust results.
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1. Preparation and packaging
NOTE: The materials/equipment to be packed is listed in Table 1. Use gloves to handle the reagents required for the process control, the concentration reagents, the nucleic acid extraction reagents and the detection reagents. Wear protective glasses to handle the reagents required for nucleic acid extraction.
2. Viral concentration
NOTE: Use gloves at all times during the sample collection, reagent preparation, flocculation, flocs collection, and waste disposal procedures. Wear protective glasses during the reagent preparation procedure.
3. Nucleic acid extraction
NOTE: Use gloves and always wear protective glasses during the nucleic acid extraction procedure.
4. Viral detection with a battery-operated eight-tube real-time thermocycler
NOTE: Use gloves and always wear protective glasses during the nucleic acid detection procedure. Replace the gloves for new ones when performing a new PCR experiment to avoid cross-contamination.
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Method development
This procedure has been developed in the Laboratory of Viruses Contaminants of Water and Food with the collaboration of GenIUL and Oxfam Intermón. It comprises of three different steps. The first one, the viral particle concentration, is an adaptation of a skimmed milk flocculation method previously described12,17,
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The VirWaTest method enables the concentration of viruses and nucleic acid extraction from water samples at the point of use by non-experienced users. It is an affordable, rapid, and simple protocol. The concentration is based on the principle of organic flocculation using skimmed milk, by which the low pH and high conductivity conditions make skimmed milk proteins aggregate into flocs the viruses adsorb to. When the flocs sediment, it is easy to collect them, making it possible to concentrate 10 L of water, whereas trad...
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The authors have nothing to disclose.
VirWaTest was a research project funded by the HIF (Humanitarian Innovation Funds) program of ELHRA (Enhancing Learning & Research for Humanitarian Assistance). The authors acknowledge the WASH teams who kindly collaborated in this study. The analysis of samples in Ecuador was funded by Oxfam Ecuador and Dirección de Investigaciones de la Universidad de las Americas (AMB.BRT.17.01). S. Bofill-Mas is a Serra-Hunter fellow at the University of Barcelona.
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| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| 5x HOT FIREPol Probe qPCR Mix Plus (ROX) | Solis BioDyne | 08-14-00001 | Includes Solis Biodyne's 5x HOT FIREPol Probe qPCR Mix Plus (qPCR Mix), 50 Reactions |
| 8-Microtube Strips with Caps | dD Biolab | 840637 | Low Profile, Thin Walls, Adapted for Quantitative and Qualitative PCR |
| Batteries and Power Adapters for Magnetic Stirrer | GenIUL | 900011674 | Includes 12V car power adapter |
| Bucket Support | GenIUL | 900011648 | Aluminium support |
| Bucket, 10 L | Cater4You | 10LTR | Polypropilene, Tamperproof, Clear color |
| Centrifuge Tube, 50 mL | LabBox | CTSP-E50-050 | Polypropylene, Sterile, Graduated, With Skirt |
| Citric Acid 1-Hydrate, 500 g | PanReac AppliChem | 1410181211 | Pure, Pharma Grade, 1 Kilogram |
| Clear PET Bottle | LabBox | FPET-500-088 | Clear Color, PET, Cap Not Included |
| Difco Skim Milk, 500 g | Becton Dickinson | 232100 | Dehydrated |
| DNA/RNA Shield, 250 mL | Zymo Research | R1100-250 | DNA/RNA Preservation Medium, 250 mL |
| Easy9 Pipette Controller | LabBox | EAS9-001-001 | 0.3 μm filter, Pipettes from 0.1 to 100 mL, Autoclavable silicone pipette holder |
| Eppendorf Tube, 0.5 mL | Eppendorf | 0030121023 | Polypropilene, Safe-Lock |
| Eppendorf Tube, 2 mL | Eppendorf | 0030120094 | Polypropilene, Safe-Lock |
| Eppendorf Tube, 5 mL | dD Biolab | 999542 | Polypropylene, Sterile, Graduated |
| Ethanol 96% V/V, 1 L | Panreac AppliChem | 361085-1611 | For UV, IR and HPLC |
| Laboratory Tweezers | LabBox | FORS-007-002 | Thin, Curved End, L= 120 mm |
| Magnetic Stirrer | GenIUL | 900017000 | Battery-powered |
| Marker | dD Biolab | 929203 | Black, Extra fine Tip, Water Resistant, Fast Drying, For Plastic and Glassware |
| Micro Rota-Rack for Microtubes | dD Biolab | 37782 | 4 Modules, L x W x H= 208 x 100 x 100 mm |
| Mini8 Real-Time PCR Cycler | Coyote Biosciences, China | Mini-8 | Portable, Works with 12V Power Supplies or External Batteries, Two channels, Capacity for 8 Tubes |
| NucliSens Lysis Buffer | Biomerieux | 200292 | Reagents for up to 48 Isolations, Store at Ambient Temperature |
| Open Tip Serological Pipette, 10 mL | Deltalab | 900136N | Sterile, Individually Wrapped (Paper/Plastic) |
| PE Screw Cap PP28 | LabBox | TP28-004-020 | For PET Bottles |
| pH Indicator Strip | LabBox | WSPH-001-001 | Range pH 2.8 to pH 4.4, 50 Strips per Pack |
| Plastic Test Tube | Quimikals | 300913 | Includes Cap |
| Polyethylene Pasteur Pipette | LabBox | PIPP-003-500 | Graduated, 7 mL Overall Volume, Non-Sterile |
| Polypropylene Screw Flask With Screw Cap, 150 mL | Deltalab | 409726 | Screw cap, Sterile, graduated up to 100 mL |
| Polypropylene Screw Flask With Screw Cap, 60 mL | Deltalab | 409526G | Screw cap, Sterile, Graduated up to 50 mL |
| Powder Powder Detergent | - | - | Regular Powder Soap for washing clothes |
| Power Cables for Magnetic Stirrer | GenIUL | 900011692 | Connection between batteries and magnetic stirrers |
| QuickPick Magnetic Tool | BioNobile | 24001 | Hand-held tool for magnetic particles |
| QuickPick Tips in Box | BioNobile | 24296 | RNase-Free, Autoclaved, 96 Units |
| QuickPick XL gDNA Magnetic Particles | BioNobile | SN51100 | 3.2 mL |
| Sea Salts | Sigma-Aldrich | S9883-500G | An artificial salt mixture closely resembling the composition of the dissolved salts of ocean water |
| Silicone Tubing | LabBox | SILT-006-005 | Roll of 5 Meters, Inner ø x Outer ø= 6 x 10 mm |
| Sodium Hydroxide Pellets, 98.5 - 100.5% | VWR Chemicals | 28244295 | Pellets, 1 Kg |
| Solar Rotary Platform | SOL-EXPERT Group | 70020 | Acrylic Plate, 10 RPM, Supports up to 300 Grams |
| SOLIScript 1-step Probe Kit | Solis BioDyne | 08-57-00250 | Includes Solis Biodyne's 5x One-Step Probe Mix (qPCR Mix) and 40x One-Step SOLIScript Mix (Reverse Transcriptase Enzyme), 250 Reactions |
| SPEEDTOOLS RNA Virus Extraction Kit | BioTools | 21.141-4197 | Includes BioTools's BAW Buffer (Washing Buffer 1), BAV3 Buffer (Washing Buffer 2 and 3) and BRE Buffer (Elution Buffer). |
| SpinBar Octhaedral Stirring Magnet | dD Biolab | 045926 | Pivot Ring, L x ø = 38 x 8 mm, Blue |
| Tape-End Serological Pipette, 10 mL | Deltalab | PN10E1 | Sterile, Individually Wrapped (Paper/Plastic) |
| Tape-End Serological Pipette, 50 mL | Deltalab | 900043 | Sterile, Individually Wrapped (Paper/Plastic) |
| Termi-DNA-Tor - Nucleic Acid Remover | BioTools | 22001-4291 | Remover of nucleic acids, bacteria, fungi and mycoplasma from material and surfaces, 450 mL |
| Water Molecular Biology Reagent, 1L | Sigma-Aldrich | W4502-1L | Nuclease and Protease Free, 0.1 μm Filtered |
| Whirl-Pak Bag, 540 mL | Deltalab | 200361 | Stable bottom |
| Zip Lock Plain Bag | LabBox | BZIP-080-100 | Polyethylene, L x W= 120 x 80 mm |
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