More research needed on Cryptosporidium, says parasitologist
The ghosts of Milwaukee are affecting Australian media coverage of the water-borne disease cryptosporidiosis, according to a University of Queensland parasitologist.
"There is considerable public misinformation about the disease cryptosporidiosis and the Cryptosporidium organism that causes it," senior lecturer in protozoology Dr Peter O'Donoghue said.
Dr O'Donoghue has been a consultant to Sydney water authorities following three incidents in which the parasite Cryptosporidium was detected in Sydney drinking water supplies this year. These events resulted in three "Boil Water" notices being issued to more than three million residents in the past few months.
He said there had been no disease outbreak in the city.
"To date, investigations by health authorities have not detected any rise in illness due to Cryptosporidium or Giardia," he said.
However, the events had brought to prominence in Australia the difficulties facing water and health authorities in dealing with the detection of protozoa in water supplies, given the current limited state of understanding of their public health implications.
Dr O'Donoghue said Cryptosporidium was discovered in 1907 and promptly forgotten for many years. Scientists related the parasite to disease in birds in the 1950s, mammals in the 1970s, and disease in humans in the 1980s.
"It has since attracted consistent medical and veterinary attention as infections have been recorded," he said.
"One of the most infamous incidents was in 1993 when 400,000 people in Milwaukee were infected by water-borne cryptosporidiosis caused by a breakdown in water treatment and effluent systems. There simply has never been an incident like that in Australia."
Dr O'Donoghue, an internationally regarded parasitologist who has studied Cryptosporidium for 20 years, said it was the smallest known coccidian parasite and its oocysts had a unique configuration in that sporocysts (or secondary spores) were absent.
Recent surveys had shown that most infections could remain asymptomatic and relatively few were associated with clinical disease, usually manifest as mild to severe diarrhoea.
"In Queensland cryptosporidiosis is a notifiable disease so we are now starting to compile useful epidemiological data on infections in communities," he said. "Queensland Health has convened several committees to prepare management protocols should an outbreak arise."
Dr O'Donoghue is a member of an expert technical working group on water supplies. The group has prepared a draft code of practice for officials and this is being reviewed by the Health Department.
Dr O'Donoghue recently was a guest speaker at a consensus conference on Cryptosporidium in Water in Melbourne, sponsored by the CRC for Water Quality and Treatment, the Water Services Association of Australia and the Australian Water and Wastewater Association
He said conference delegates resolved that tests were needed to determine parasite viability and the efficacy of treatment processes and disinfection, as current techniques were not very sensitive and molecular innovations were yet to be validated. They also resolved that Australia needed to establish a library of organisms so researchers could conduct biological and molecular characterisation studies on parasite isolates of known identity.
"This will help scientists to genetically type isolates to indicate the sources of water contamination, be they animal or human," he said.
He said researchers had only just begun to address such questions as whether detected parasites present were alive or dead? Were they infective only for animals or for humans? Where had they come from and how long could they survive? Were surveillance mechanisms adequate? How many outbreak situations had occurred? How could authorities determine the actual risks?
His current research uses genetic typing to help locate the source of the parasites, using clinical isolates to determine whether they show differences in infectivity, virulence and pathogenicity.
"We are taking the most extreme examples, that is strains of high and low virulence and looking for distinct genetic differences to make sense of their genetic variation," he said.
Certain patient groups appeared to be at higher risk of clinical infection, especially infants and immuno-compromised individuals (people undergoing immuno-suppressive chemotherapy or having congenital or acquired immuno-deficiencies), he said.
Dr O'Donoghue was awarded his PhD from the University of Adelaide in 1979 and was an Alexander von Humboldt postdoctoral research fellow at the Institute for Comparative Tropical Medicine and Parasitology in Munich in 1980 and the Hanover Veterinary University in 1981. He joined the Institute of Medical and Veterinary Science in Adelaide before moving to the University of Queensland in 1994 as senior lecturer in protozoology.
Media contact: Dr O'Donoghue, telephone 07 3365 2584, email: p.odonoghue@mailbox.uq.edu.au
