viruses in drinking water grabow

8/11/2019 Viruses in Drinking Water Grabow

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Presented at the WISA 2000 Biennial Conference, Sun City, South Africa, 28 May to 1 June 2000

VIRUSES IN DRINKING WATER

W O K Grabow, M B Taylor, C G Clay and J C de Villiers

Department of Medical Virology, University of Pretoria

Abstract

Viral infections have a long history of association with drinking water supplies. Evidence of water-

borne transmission is predominantly based on epidemiological data. Water-borne transmission has

only in exceptional cases been confirmed by direct detection of viruses in drinking water supplies. This

is because the majority of viruses typically transmitted by water (enteric viruses) are not detectable by

conventional methods. However, molecular techniques based on the reverse transcriptase-polymerase

chain reaction (RT-PCR) available now, have made it possible to detect low levels of a wide variety

of enteric viruses. This preliminary study deals with 411 analyses of drinking water supplies carried out

over a period of two years. The drinking water supplies were derived from acceptable quality surface

water sources using generally accepted treatment and disinfection processes. Glass wool filters were

used for the on-site and in-line recovery of viruses from 100 to 1000 litre volumes of water. Viruses

eluted from the glass wool were inoculated onto combinations of cell cultures including the BGM

monkey kidney, PLC/PRF/5 human liver and CaCo-2 human colon carcinoma cell lines, as well as

primary vervet monkey kidney cells. The purpose of cell culture inoculation was to isolate

cytopathogenic viruses, to amplify the nucleic acid of non-cytopathogenic viruses, and to confirm

viability of viruses. After two passages cell cultures were homogenised and analysed by RT-PCR for

a variety of enteric viruses. Positive results were recorded for 24 % of the samples. Enteroviruses

were detected in 17 % of the samples, adenoviruses in 4 % and hepatitis A virus in 3 %. None of the

viruses were cytopathogenic, which implies that they would not be detected by conventional cell culture

propagation techniques. These findings are in agreement with reports on the detection of viruses in

drinking-water supplies in other parts of the world. The results also support epidemiological studies

which indicate low level transmission of viral infections by drinking water supplies which have been

treated and disinfected by acceptable procedures and meet quality specifications for indicators such as

coliform bacteria. All the water supplies analysed in this study had heterotrophic plate counts of less

than 100/1 ml, total and faecal coliform counts of 0/100 ml, and negative results in qualitative presence-

absence tests for somatic and F-RNA coliphages on 500 ml samples. These findings support earlier

evidence on shortcomings of conventional indicators for assessment of the virological quality of drinking

water. The results have various implications. For instance, the water supplies analysed here, and

probably many others, would fail national and international quality guidelines which state that drinking

water should be free of viruses. However, since these guidelines are based on outdated viral detection

methods, they may be considered due for revision to accommodate new molecular technology. This

may not be an easy decision because the viruses detected by the technology described here are at least

potentially infectious and may be regarded to constitute a health risk. Retention of the existing

guidelines would have major cost and technical implications for the water industry. The results of thisinvestigation underline the need for more detailed studies.


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Introduction

Drinking water supplies have a long history of association with a wide spectrum of viral infections.

Evidence of water-borne transmission is predominantly based on epidemiological data. Water-borne

transmission has only in exceptional cases been confirmed by direct detection of viruses in drinking

water supplies. This is because the majority of viruses typically transmitted by water (enteric viruses)

are not detectable by conventional methods. However, molecular techniques based on the reverse

transcriptase-polymerase chain reaction (RT-PCR) available now, have made it possible to detect low

levels of a wide variety of enteric viruses (Grabow, 1996).

Materials and Methods

A total of 411 samples of drinking water collected at regular intervals over a period of two years were

analysed. The supplies were derived from acceptable quality surface water sources using treatment

processes which conform to international specifications for the production of safe drinking water.

Disinfection was by chlorination based on corresponding specifications for concentration levels and

conditions of application. Glass wool filters were used for the on-site and in-line recovery of viruses

from 100 to 1000 litre volumes of water (Vilagins et al. 1997). Viruses eluted from the glass wool

were inoculated onto combinations of cell cultures including the BGM monkey kidney, PLC/PRF/5

human liver and CaCo-2 human colon carcinoma cell lines, as well as primary vervet monkey kidney

cells. The purpose of cell culture inoculation was to isolate cytopathogenic viruses, to amplify the

nucleic acid of non-cytopathogenic viruses, and to confirm viability of viruses. After two passages cell

cultures were homogenised and analysed by RT-PCR for a variety of enteric viruses (Grabow et al

1999). Corresponding samples of water were analysed for microbial indicators of water quality using

internationally accepted techniques and principles (Grabow, 1996).

Results

Viruses were detected in 24 % of the samples. Entero viruses were detected in 17 %, adeno viruses

in 4 % and hepatitis A virus in 3 %. None of the viruses were cytopathogenic, which implies that they

would not be detected by conventional cell culture propagation techniques. All the water supplies had

heterotrophic plate counts of less than 100/1 ml, total and faecal coliform counts of 0/100 ml, and

negative results in qualitative presence-absence tests for somatic and F-RNA coliphages on 500 ml

samples.

Discussion

The findings are in agreement with reports on the detection of viruses in drinking water supplies

elsewhere in the world (Payment et al 1997, Grabow 1996, Rose et al. 1986). The results also

support epidemiological data which indicate low level transmission of viruses by drinking water supplies

which have been treated and disinfected by standard procedures and meet quality specifications for

indicator bacteria. The results for heterotrophic plate counts, coliform bacteria and coliphages are inagreement with earlier evidence on shortcomings of conventional indicators for assessment of the

virological quality of drinking water (Grabow, 1996).


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Implications of the results include:

1. The water supplies analysed here, and probably many others likewise derived from acceptable

sources using standard procedures of treatment and disinfection, would fail quality guidelines which

specify the absence of viruses from drinking water (WHO 1997, 1996, EPA 1989, EEC 1980).

However, since these guidelines are based on outdated viral detection methods, they may be

considered due for revision to accommodate new technology for the detection of viruses. Decisions in

this regard would have to take into consideration that the viruses detected by the technology used here

are at least potentially infectious and may constitute a health risk. Retention of the existing guidelines

would require substantial improvement in treatment and disinfection to eliminate viruses detectable by

molecular techniques.

2. One option to accomplish existing goals for the absence of viruses from drinking water would be to

intensify chlorination, which may escalate potential risks of health effects associated with disinfection

by-products.

3. The failure of conventional indicator tests to prove the absence of viruses from drinking water

supplies has implications for water quality monitoring procedures. The failure of even sensitive tests for

somatic and F-RNA coliphages in 500 ml samples to reflect the presences of viruses, suggests that the

shortfall of indicator procedures may be substantial. This suggests the sensitivity of microbial indicator

tests may have to be upgraded significantly to reflect the virological safety of drinking water supplies.

4. Improving the efficiency of water treatment and disinfection processes to eliminate viruses

detectable by molecular techniques, and increasing the sensitivity of microbial indicator tests to reflect

the absence of viruses detectable by these techniques, are likely to have major financial implications for

the water industry.

References

EEC (1980) Council Directive of 15 July 1980 relating to the quality of water intended for human

consumption (80/778/.EEC). Official J European Commun No L229:11-22.

EPA (1989) Maximum contaminant level goals for microbiological contaminants. Federal Register,

Part II, Environmental Protection Agency, Part 141.52, p 27527.

Grabow W O K (1996) Waterborne diseases: Update on water quality assessment and control.

Water SA 22:193-202.

Grabow W O K , Botma K L, de Villiers J C, et al. (1999) An assessment of cell culture and PCR

procedures for the detection of polio viruses in waste water. Bull WHO (in press).

Payment P, Siemiatycki J, Richardson L, et al. (1997) A prospective epidemiological study of

gastrointestinal health effects due to the consumption of drinking water. Int J Environ Hlth Res 7:5-31.

Rose JB, Gerba CP, Singh SN, et al. (1986) Isolating viruses from finished water. Res Technol

78:56-61.

Vilagins P, Sarrette B, Champsaur H, et al. (1997) Round robin investigation of glass wool methodfor poliovirus recovery from drinking water and sea water. Water Sci Technol 35:455-460.


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WHO (1996) Guidelines for drinking-water quality. Vol 2: Health criteria and other supporting

information. Second edition. World Health Organization, Geneva, pp 10-99.

WHO (1997) Guidelines for drinking-water quality. Vol 3: Surveillance and control of community

supplies. Second edition. World Health Organization, Geneva. 238 pp.

Prof W O K Grabow

T : (012) 319-2351

F : (012) 325-5550

E : [email protected]

viruses in drinking water grabow

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