Giardia lamblia which parasitize humans belong to either of two genotypes, A or B, based on specific signature sequences in the 5' end of the small subunit (16S) ribosomal RNA (rRNA) gene. These two genotypes also were found in cysts from fecal samples of animal origin such as dogs, cats, some farm animals and wild animals. In addition, trophozoites recovered from cysts obtained from environmental samples belonged to these two genotypes as well, suggesting that the G. lamblia genotypes A and B are widespread and possibly zoonotic. Trophozoites were recovered from rats and these isolates might belong to another genotype of G. lamblia. Deer mice and one dog appeared to be parasitized by genotypes of Giardia with close affinity to G. microti. This species, therefore, also consists of a genotype complex.

The reported incidence of waterborne disease is increasing in North America, and the provision of drinking water and sewage treatment is confronted with a growing population base and either an aging or developing infrastructure. To combat this trend, North American drinking water standards are continuously reviewed and increased effort is being expended to monitor and improve the quality of sewage and water treatment. in this regard Federal, Territorial and First Nation agencies have been working to improve community infrastructures within the Yukon. The Territory's location north of 60 degrees, cultural demographics, and the progress of First Nation self government initiatives, presents challenges in the delivery of these programs that are not encountered in southern Canada. A study of Yukon communities was conducted in 1995 to produce a current compilation of services as they existed at the time. A summary of the existing infrastructure, policy and program background, unique aspects of program delivery, and future development are examined.

This study was carried out to estimate the prevalence and potential for human infectivity of Giardia cysts in Canadian drinking water supplies. The presence of Cryptosporidium oocysts was also noted, but isolates were not collected for further study. A total of 1,760 raw water samples, treated water samples, and raw sewage samples were collected from 72 municipalities across Canada for analysis, 58 of which treat their water by chlorination alone. Giardia cysts were found in 73% of raw sewage samples, 21% of raw water samples, and 18.2% of treated water samples. There was a trend to higher concentration and more frequent incidence of Giardia cysts in the spring and fall, but positive samples were found in all seasons. Cryptosporidium oocysts were found in 6.1% of raw sewage samples, 4.5% of raw water samples, and 3.5% of treated water samples. Giardia cyst viability was assessed by infecting Mongolian gerbils (Meriones unguiculatus) and by use of a modified propidium iodide dye exclusion test, and the results were not always in agreement. No Cryptosporidium isolates were recovered from gerbils, but 8 of 276 (3%) water samples and 19 of 113 (17%) sewage samples resulted in positive Giardia infections. Most of the water samples contained a low number of cysts, and 12 Giardia isolates were successfully recovered from gerbils and cultured. Biotyping of these isolates by isoenzyme analysis and karyotyping by pulsed-field gel electrophoresis separated the isolates into the same three discrete groups. Karyotyping revealed four or five chromosomal bands ranging in size from 0.9 to 2 Mb, and four of the isolates had the same banding pattern as that of the WB strain. Analysis of the nucleotide sequences of the 16S DNA coding for rRNA divided the isolates into two distinct groups corresponding to the Polish and Belgian designations found by other investigators. The occurrence of these biotypes and karyotypes appeared to be random and was not related to geographic or other factors (e.g., different types were found in both drinking water and sewage from the same community). Biotyping and karyotyping showed that isolates from this study were genetically and biochemically similar to those found elsewhere, including well-described human source strains such as WB. We conclude that potentially human-infective Giardia cysts are commonly found in raw surface waters and sewage in Canada, although cyst viability is frequently low. Cryptosporidium oocysts are less common in Canada. An action level of three to five Giardia cysts per 100 liters in treated drinking water is proposed on the basis of the monitoring data from outbreak situations. This action level is lower than that proposed by Haas and Rose (C. N. Haas and J. B. Rose, J. Am. Water Works Assoc. 87(9):81-84, 1995) for Cryptosporidium spp. (10 to 30 oocysts per 100 liters).

Several outbreaks of waterborne giardiasis have occurred in southern Canada, but nothing has been reported from the Canadian North. The objective of this study was to collect information relevant to waterborne giardiasis and cryptosporidiosis in the Yukon including epidemiological data and analyses of water, sewage, and animal fecal samples. Remote, pristine water samples were found to be contaminated with Giardia cysts (7 of 22 or 32%) but not with Cryptosporidium oocysts. Giardia cysts were found in 21% (13 of 61) of animal scats, but no Cryptosporidium oocysts were observed (small sample size). Whitehorse's drinking water was episodically contaminated with Giardia cysts (7 of 42 or 17%) and Cryptosporidium oocysts (2 of 42 or 5%). Neither were found in Dawson City's water supply. The only water treatment in the Yukon is chlorination, but contact times and free chlorine residuals are often too low to provide adequate protection by disinfection. Raw sewage samples from the five largest population centers in the Yukon contained 26 to 3,022 Giardia cysts and 0 to 74 Cryptosporidium oocysts per liter. Treated sewage from Whitehorse contained fewer Giardia cysts but more Cryptosporidium oocysts on average. Both were detected in Lake Laberge, downstream of Whitehorse, which has a history of fecal coliform contamination. Daily monitoring of raw sewage from the suburbs of Whitehorse showed a summertime peak of Giardia cysts and occasional Cryptosporidium oocysts after springtime contamination of drinking water. Despite this evidence, epidemiological data for the Yukon showed an endemic infection rate of only 0.1% for giardiasis (cryptosporidiosis is not notifiable).(ABSTRACT TRUNCATED AT 250 WORDS)

This study was conducted to assess the prevalence and zoonotic potential of giardiasis in domestic ruminants. Prevalence of infection was 17.7% in sheep and 10.4% in cattle and was significantly higher in lambs and calves (35.6% and 27.7%, respectively). Naturally infected lambs released cysts intermittently for months. Giardia trophozoites from sheep had typical claw hammer-shaped median bodies and were successfully cultured in TYI-S-33 medium, and cytosolic, cytoskeletal, and membrane fractions exhibited protein profiles similar to human isolates (WB). Immunoblotting showed that sera from infected sheep recognized human Giardia, sera from patients with giardiasis recognized Giardia from sheep, and in both cases recognition involved antigenic proteins of similar molecular weight. Cyst output and clinical signs in ovine infection resemble human disease and the organisms infecting humans and ruminants are morphologically and antigenically similar. It is postulated that domestic ruminants may be a reservoir for human infection and vice versa, thus classifying giardiasis as a zooanthroponotic disease.

Metronidazole, tinidazole and dimetridazole were administered in the drinking water for 5 days to mice experimentally infected with Tritrichomonas muris and Tetratrichomonas microta. Mice were successfully infected with T. muris and T. microta recovered from infected gerbils. The trichomonas infection was successfully eliminated in mice given a 1% sucrose solution containing 2·5 mg/ml metronidazole or tinidazole. Mice receiving 1·0 mg/ml metronidazole, 1·0 mg/ml tinidazole and 1·2, 5·0 and 10·0 mg/ml dimetridazole failed to eliminate the trichomonas organism. A reduction in water intake was only noted with mice receiving 10 mg/ml dimetridazole. In mice receiving only 1% sucrose the infection was not eliminated.