Our municipal water treatment systems are not fail-proof when it comes to eliminating waterborne parasites in potable water. Two protozoan parasites in particular are known to break through the system and cause disease in those drinking from this water supply.

Cryptosporidium parvum, a coccidian parasite with a world-wide distribution, is transmitted via the fecal-oral route through water, which is considered the major mode of dissemination of its oocysts. Each oocyst contains four sporozoites that are resistant to many drinking water treatment processes and which can cause gastrointestinal illness that can become life threatening in individuals with impaired immune systems such as cancer, AIDS patients and persons having transplant operations.

Cryptosporidium has been linked to many waterborne disease outbreaks, the most notable being in Milwaukee, Wisconsin, where 430,000 residents became ill, 105 of whom died. Closer to home, a 1993 outbreak in Kitchener-Waterloo resulted in an estimated 1000 persons becoming ill. Domestic cattle have been implicated as a source of the Cryptosporidium oocysts.

Giardia lamblia is a flagellated protozoan parasite of the small intestine that exists in two forms ­ a cyst, which is the resistant, transmissive stage, and a trophozoite, which is the feeding, multiplying and pathogenic stage that results in diarrhea for its host. Again, the infection is caused via the fecal-oral route and waterborne outbreaks have been well documented. This parasite is found in humans, domestic pets and wildlife.

Traditionally, the US Environmental Protection Agency method, which has been evaluated world-wide, was used to confirm the presence of these parasites.

The percent recovery of Cryptosporidium and Giardia using this method was found to consistently range from two to ten. The "Achilles heel" of this complex, multi-step procedure was the difficulty encountered in removing the oocysts and cysts from the polypropylene-wound fibre filter that the large volume of water had been filtered through. This method also required two and a half days to analyze one sample for these parasites.

In contrast to the EPA method, a new procedure has been refined that offers a percent recovery averaging approximately sixty and allows up to five samples to be processed in one day. This process is now being offered by GAP EnviroMicrobial Services Inc.

The GAP staff have been actively involved in the development of a Cryptosporidium and Giardia recovery procedure with colleagues from the Ministry of Health, Ministry of Agriculture and Rural Affairs and the University of Guelph. This team of scientists developed and refined a method called the Membrane Filter Dissolution Technique. It was conceived by John Aldom and Abdul Chagla, of the Ministry of Health, and has been optimized and field-tested by GAP staff, Garry Palmateer and Shelley Unger, in many water treatment plants managed and operated by the Ontario Clean Water Agency.

The field testing, which revealed the OCWA plants to be free of the parasites, clearly demonstrated the advantage of the technique. More than one thousand litres of water are filtered, then the filter is dissolved and all of the filter residue is captured. From the residue contents, the Cryptosporidium oocysts and Giardia cysts are selectively stained with a monoclonal antibody stain complex.

GAP staff have developed a field sampling kit containing a filter that was designed by the Millipore Corporation specifically for the recovery of Cryptosporidium and Giardia from water utilizing the filter dissolution concept. The simplicity of the sampling kit, which contains pressure tubing connected to a back pressure gauge, a water volume totalizer and the special Millipore filter, makes the sampling procedure very "user friendly".

In twenty-four hours, the results of the testing can indicate the concentration, usually expressed per 100 litres, of the Cryptosporidium oocysts and/or Giardia cysts present.

Cryptosporidium is confirmed by demonstrating the presence of the four sporozoite nuclei within the oocyst.

If the viability of the oocysts is required, a further test is performed that exhibits the potential for excystation of the sporozoites from the oocyst. The oocysts are incubated in a medium that promotes the rupturing of the oocyst wall, which allows the sporozoites to exit the oocyst. This process only occurs if the oocyst is viable.

The complete method of recovery and identification, including the viability testing, takes forty-eight hours.

The method used above relates to the testing of treated water. A similar procedure (where only 100 to 200 litres of water are filtered) is employed for the source-water of the treatment plants. Field sampling equipment, including portable gas-powered pumps, is utilized to conduct the sampling in remote areas.

When monitoring is needed for surveillance purposes as part of a Quality Control/Quality Assurance program, or when a potential outbreak occurs, trained field and laboratory staff can provide this service on a 24 hour basis.