A recent conference highlighted the dangers of the water-borne pathogen, Cryptosporidium. Dick Ahlstrom reports
'Boil water" notices may become more common given the increasing incidence of a dangerous organism that lives in lakes, streams and other water supplies. It is often fatal for those with reduced immunity and causes misery for healthy individuals who contract it.
The organism in question is Cryptosporidium parvum, a protozoan or single-celled creature spread by contact with human and animal waste. It provided the subject for a major all-Ireland conference late last month at the University of Ulster, Coleraine, that attracted experts from Ireland and Britain.
"It is the sort of organism that could cause a major outbreak," said Dr John Moore, a clinical research scientist at the Northern Ireland Public Health Laboratory in Belfast City Hospital. He helped organised the conference and runs an active research programme on the organism in conjunction with Dr James Dooley of UU Coleraine.
"The big problem we have with it is we don't have a cure for it," says Moore. "My concern is that most of the outbreaks in the literature are water-born outbreaks. Water chlorination doesn't take this organism out."
It is no stranger to this island. It was the cause of a "boil water" notice issued earlier this year in Co Westmeath during the worst episode of water-supply contamination in the State. The warning was issued to 25,000 people after the organism was found in Lough Owel, which supplies 40 per cent of the county's water. At least 26 people were treated for cryptosporidiosis, symptoms of which include severe diarrhoea, vomiting and stomach cramps.
Moore, Dooley and colleagues detailed three recent outbreaks in Northern Ireland in the US Centres for Disease Control publication, Emerging Infectious Diseases. All three occurred over the past year, all were in Belfast, and at least 476 cases were involved.
"These are some of the biggest gastrointestinal outbreaks we have ever seen," says Moore. About a fortnight ago, 140,000 households in Glasgow were asked to boil their water because of cryptosporidium.
"The natural habitat of this organism is warm-blooded animals," he explains. Animal or human waste is the usual source of an outbreak, which spreads easily in water supplies. It has evolved a special resting state between hosts as an "oocyst" which is like a "highly resistant seed", he says. "It forms a resting dormant stage that is environmentally resistant and survives for a long time."
Delegates to the conference also heard that the organism had potential as a bioterrorism agent given that few oocysts were required to spark an infection. It is also difficult to isolate in water supplies, says Moore. The organism has "huge political ramifications" because of its potential impact on public health, he says. If water supplies become infected, water used in food- processing and even for cleaning equipment poses a risk.
A key element of the research pursued by Moore and Dooley relates to the issue of detection. "You are looking for the proverbial needle in the haystack," he says.
Water authorities in Britain, by law, had to achieve oocyst levels of no more than one oocyst per 10 litres of water, although, says Moore, "I don't know if that means the water is safe or not safe. That doesn't necessarily mean there are no implications of having that level in the water."
The research group is looking at DNA-based detection methods, relying on polymerase chain reaction (PCR) technology.