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Virus Busters

Virus contamination in New Zealand waters are a concern for two researchers in environmental virology, who are using cell culture and sensitive molecular techniques to better understand viral contaminants in shellfish and water.

Dr Gail Greening of the Institute of Environmental Science and Research and Dr Gillian Lewis of Auckland University, are also evaluating the effectiveness of different ways of detecting viruses, using the data to create virus survival and distribution models that will help predict contamination.

Greening says the occurrence of human viruses in natural waters, including shellfish-growing waters, indicates that they have been contaminated by human faecal wastes and are a risk to human health.

"In particular, filter-feeding shellfish concentrate environmental contaminants and serve as enriched sources of infectious viruses," Greening says. "The risk to people from contaminated water and shellfish, and the probability of resulting disease, need to be estimated."

This raises many questions. For example, are the viruses infectious? What is the risk to human health? Is it a resource quality or human health issue, or both? What is the source of contamination and can we trace it? Should we routinely monitor for viruses?

"To answer these questions we need to know more about the types and behaviour of contaminant viruses likely to be present in the environment."

The common human virus contaminants are those that replicate within the gastrointestinal tract or upper respiratory system. They all show resistance to adverse environmental conditions and are not easily suppressed.

"We have now developed sophisticated methods for detecting these viruses in environmental samples," Greening says.

Survival studies have shown that 87% of seeded infectious poliovirus persist in chilled mussels after two days at 4oC, and 54% persist in frozen mussels after one month. In natural waters, viral persistence seems to depend mainly on temperature and the quantity of clays and bacteria present as well.