In 1996, cryptosporidium sickened about 2,000 people in Cranbrook, B.C. An outbreak in Kelowna, B.C., weeks later caused an estimated 10,000 to 15,000 people to become ill with the gastrointestinal illness caused by the parasite.

Such disease-causing microbes are shed by domestic animals like cattle and sheep, as well as by wild animals, contaminating surface water that can lead to disease outbreaks in people.

“There’s a long human history of consuming raw water over millennia and centuries and that has resulted in numerous documented outbreaks of serious infectious diseases and fatalities,” Dr. Ray Copes, chief of environmental and occupational health at Public Health Ontario, said Friday.

But public health experts advise Canadians against embracing the raw water fad, saying untreated water can carry a host of micro-organisms that may cause severe illness and even death.

For instance, giardia — also known as “beaver fever” — has been known to infect campers and canoeists who drink from lakes and rivers, she noted.

A case in point is the May 2000 outbreak in Walkerton, Ont., of E. coli 0157:H7, a virulent strain that sickened about 2,500 residents and killed seven as the result of a contaminated water supply. The E. coli is believed to have originated in seeping groundwater adulterated by cattle at nearby farms.

“Most of these pathogens are from fecal contamination … from a human or livestock source,” Sargeant said in an emailed interview. “Even the most pristine water could be contaminated from wildlife feces.”

Contaminated wells and groundwater are also responsible for hundreds of boil-water advisories in effect in remote communities across Canada, some of which have been in place for decades.

“We have to be aware that there are many species out there that are defecating, that are emptying the contents of their enteric tracts onto the land and into the water,” he said.

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