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Virological analysis of drinking water using molecular biological methods

Research partner:
Swiss Federal Institute of Aquatic Science and Technology (EAWAG), Dübendorf
Dr. T. Egli
http://www.eawag.ch

Background

Given the difficulty associated with their detection, there is no standardised monitoring of viruses [Hygiene Ordinance, 2002]. In fact, samples are only taken sporadically from smaller drinking water reservoirs. Surprisingly, very little is known about viral contamination of drinking water. Therefore, it would be beneficial to improve our knowledge in this area.

It is thought that sporadic outbreaks of diarrhoea are caused by low concentrations of pathogenic viruses in the drinking water [WHO, 1979]. It is difficult to support this hypothesis, as it refers to isolated cases where the registration of patients was incomplete. Furthermore, clinical samples are rarely analysed for the presence of viruses.

Aim of the project

Thanks to their high sensitivity and selectivity, molecular biological methods (PCR, real time PCR, in situ hybridisation etc.) allow for more detailed analyses. By applying such methods, we should be able to identify viruses present in selected drinking water reservoirs of the Swiss army.

Incorporating data provided by army doctors should allow us to investigate whether there is a correlation between the number of cases of diarrhoea and the virus contamination of drinking water.

Based on our practical experience with molecular biological methods we should be able to determine the best suited method for a rapid detection of viruses in drinking water.

Content

1. Evaluation of methods to detect viruses in drinking water.

Although current molecular biological methods such as PCR or in situ hybridisation are faster and more precise, but their application in drinking water analysis is still far from standardisation.

There are already a few highly promising molecular biological methods on the market to detect specific micro-organisms. The aim of the present research project is not to develop new detection methods, but to adapt existing methods.

Following methods will be evaluated for their application in drinking water analysis:

• PCR
• Real Time PCR for quantitative analysis
  

The given methods should be investigated in terms of the following criteria:

• Determination of the detection limit for specific viruses;
• Determination of selectivity
• Determination of robustness in relation to environmental influences (e.g. inhibitory substances)

2. Characterisation of the virus population in selected drinking water reservoirs of the Swiss army:

A number of drinking water reservoirs belonging to the Swiss army will be selected. They will be classified into a number of categories according to catchment area (alpine, karst, agricultural, urban etc.). A series of measurements will be taken over different time periods (24 hours, 1 month, 1 year) which will enable us to estimate the fluctuation range. In addition, we shall compare measurements taken before and after heavy rainfall.

The following viruses should be included:

• Coliphage (faecal indicator)
• Rotavirus (pathogen)
• Norwalk virus (calicivirus) (pathogen)
• Coliphage (faecal indicator)

And possibly:

• Adenoviruses (pathogen)
• Poliovirus (pathogen)
• Hepatitis E

3. Data analyses

The collected data should enable us to examine the following open questions.

1. Correlation between diarrhoea outbreaks and the virus contamination of drinking water.
2. Influence of the surroundings of the drinking water reservoirs on the virus load of the drinking water.
3. Influences of dissolved nutrients on the virus load.
4. Monitoring of drinking water.
5. Influence of biofilm on the virus load present in pipelines.

4. Online monitoring of viruses in drinking water

Currently, no technology exists for the online control of specific viruses in drinking water. Therefore, we shall propose a three-stage measurement system. The starting point will be a simple method to detect viruses in drinking water. If a given threshold is exceeded, the virus load is determined using a second unspecific method. If the procedure confirms a significant increase of viruses, real-time PCR is used for their identification.

Parameters which are best suited for the online control should be determined.

Real-time PCR is used to take specific measurements.

References

Grabow W. O. K. (1996). Waterborne diseases: Update on water quality assessment and control. Water SA 22, 193-202.

Hygieneverordnung (2002). Verordnung über die hygienischen und mikrobiologischen Anforderungen an Lebensmittel, Gebrauchsgegenstände, Räume, Einrichtungen und Personal. In der schweizerischen Hygieneverordnung.
Payment P., Trudel M. & Plante, R. (1985). Elimination of viruses and indicator bacteria at each step of treatment during preparation of drinking water at seven water treatment plants. Appl. Environm. Microbiol. 59, 2418-2424.

Walter R. (2000). Umweltvirologie - Viren in Wasser und Boden. Slovenia: Springer-Verlag.

WHO (1979). Human viruses in water, wastewater and soil. Geneva: World health organisation (WHO).