Breakthrough in battling waterborne threat

EVERY year the thousands of Australians visiting developing countries take stringent precautions to prevent gastrointestinal illnesses.

However, waterborne health threats could be closer to home than many realise. Murdoch University research has developed a novel DNA test to detect a waterborne parasite which poses a serious health threat in developed and undeveloped countries alike - and to identify whether the source of an outbreak is animal or human.
The parasite is Cryptosporidium parvum, a parasite small enough to pass through the water filters of most water authorities and resistant to chlorination procedures for disinfecting water.
The test is an international first. It was developed by researchers from the School of Veterinary Studies' Institute for Molecular Genetics and Animal Diseases (IMGAD), working with the State Agricultural Biotechnology Centre.
It is also a significant advance upon the time-consuming and insensitive conventional testing techniques, which usually involve the microscopic examination of faeces or filtered water.
As there are no effective drugs or vaccines available for cryptosporidiosis, a diagnostic tool capable of determining the source of the outbreak would be invaluable to water and medical authorities.
Children
Waterborne outbreaks of cryptosporidiosis have been recorded around the world. The disease is a significant cause of diarrhoeal illness, particularly in young children and the immunocompromised, as well as livestock such as cattle and sheep.
As many as 10 per cent of people with AIDS in the United States are reported to suffer from severe and unremitting cryptosporidiosis.
The disease is also prevalent in day care centres, where close contact between children and a lack of toilet training contribute to the spread of the disease.
The most severe outbreak occurred in 1993 in the United States city of Milwaukee, where over 400,000 people contracted cryptosporidiosis as a result of drinking contaminated water.
An ongoing outbreak in British Columbia has affected hundreds of people.
"In an outbreak situation a test to determine whether it has an animal or human source would be very useful," says Dr Una Morgan, who developed the molecular tool as part of her doctoral studies.
Cryptosporidium infects a wide range of mammals, including cattle, and it is presumed that it is transmissible from animals to humans.
"Large outbreaks are often caused by heavy run-off from infected pastures close to the water supply and breakdowns in the filtering and purification systems of water authorities," she says.
Motivation
The limitations of conventional diagnostic approaches motivated Dr Morgan and her colleagues to develop the test, which uses sensitive polymerase chain reaction (PCR) primers for detection and diagnosis of the parasite and identification of its source. Dr Morgan describes PCR as a powerful technique for amplifying DNA.
"What we can now do is differentiate between Cryptosporidium from animal and human sources. The PCR product from parasites from animal isolates are smaller in size than those from a human source.
Knowing the source of infection could help authorities to track down and deal with the source of the outbreak.
Dr Morgan said that the PCR test can detect as little as one Cryptosporidium oocyst (the parasite's environmental stage) and is specific for that particular parasite.
Dr Morgan and her colleagues also plan to develop a Multiplex PCR Test, to simultaneously detect three parasites; Cryptosporidium and two other enteric parasites Giardia duodenalis and Cyclospora, which also cause diarrhoeal illness. While the latter cause illness, they are treatable by drugs. An ability to differentiate between the pests is, therefore, essential.
So far IMGAD has tested the sensitivity of the Cryptosporidium test by screening known positive samples from local hospitals.
Next year the Institute will enter into a collaborative blind trial with pathology laboratory Western Diagnostics.
"Western Diagnostics will send us faecal samples that have been screened for Cryptosporidium, but won't reveal the result," says Dr Morgan.
"We will then screen the samples with the PCR test, which will give us a direct comparison between PCR and conventional detection techniques and an assessment of how sensitive the PCR test is."
Collaboration
The Institute is also planning to collaborate with some large pathology laboratories in the United States and a water authority in the United Kingdom to trial the PCR test under their conditions.
The commercial applications for the molecular diagnostic tool are promising. IMGAD has already filed a patent on its invention, and is seeking further research and development funding.
In the United States, testing for Cryptosporidium in water systems serving over 10,000 people was made mandatory last year, which makes the development of tools for the detection of the parasite even more vital.