Waterborne Cryptosporidiosis and the Need for Legislation

Abstract

In the January issue of Parasitology Today, Smith and Rose[1xSmith, H.V. and Rose, J.B. Parasitol. Today. 1998; 14: 14–22Abstract | Full Text | Full Text PDF | PubMed | Scopus (180)See all References[1]presented an excellent review on waterborne cryptosporidiosis. Cryptosporidiosis is an emerging disease that has recently received much attention not only from parasitologists, but also from physicians, veterinarians, environmentalists, engineers, and (very soon) legislators. Cryptosporidium parvum, an intestinal protozoan that was described for the first time less than 100 years ago, is an opportunistic organism; it is an enteropathogen in immunologically immature or immunocompromised hosts[2xEsteban, J.G. et al. Am. J. Trop. Med. Hyg. 1998; 58: 50–55PubMedSee all References[2]. A recent study[3xSee all References[3]on the prevalence of cryptosporidiosis in calves in the 12 agricultural regions of the Province of Quebec, Canada involved 2000 fecal specimens, which were concentrated by sucrose, smeared on slides and acid-fast stained before examination by microscope under oil for identification of C. parvum oocysts. The infection was present in all regions with the percentage of positive calves varying between 84 and 92%. This prevalence is similar to that reported in other countries[4xFayer, R. and Ungar, B.L.P. Microbiol. Reviews. 1986; 50: 458–483PubMedSee all References[4]. As manure is used as a source of organic fertilizer in the field, it has been suggested that agricultural practices play an important role in the spread of infection. We have also investigated the transmission of infection in calves kept in a barn, by following the occurrence of infection in cows one week prior to calving; cows which do not show any symptoms of disease (diarrhea), nevertheless pass oocysts in their feces, hence contaminating the area reserved for calving. Even immunologically mature cows, therefore, may be a source of contamination for the calf, and may also contribute to contamination of the environment.To my knowledge, there are no documented cases of waterborne cryptosporidiosis in Canada; but this does not mean that outbreaks have never occurred there, as all the parameters necessary for its occurrence are present. A recent study by Wallis et al.[5xWallis, P. et al. Appl. Env. Microbiol. 1996; 62: 2789–2797PubMedSee all References[5]on the prevalence of Cryptosporidium oocysts in drinking water in Canada involved a total of 1760 untreated, treated, and raw sewage water samples from 72 municipalities (only 58 of which treated their water by chlorination alone). Cryptosporidium oocysts were found in 6.1% of raw sewage samples, 4.5% of untreated water samples, and 3.5% of treated water samples—a prevalence lower than that reported in other countries[1xSmith, H.V. and Rose, J.B. Parasitol. Today. 1998; 14: 14–22Abstract | Full Text | Full Text PDF | PubMed | Scopus (180)See all References[1]. Several factors could explain this low percentage of positivity in Canadian water[4xFayer, R. and Ungar, B.L.P. Microbiol. Reviews. 1986; 50: 458–483PubMedSee all References[4]: (1) the amount of rain and snow that falls on the Canadian land makes this country one of the richest in the world for fresh water, therefore it is possible that the volume of water that flows into Canadian rivers and the size of the lakes contribute as a diluting factor; and (2) the oocysts become more difficult to detect and/or do not exist in sufficient quantity to affect the quality of surface water. In spite of that, the danger of contamination still exists in Canada since the number of cattle in the whole country is 13.2 million head (1.415 million head in Quebec alone)—a fair potential for contamination not only of surface water, but of humans and wildlife as well.In their review, Smith and Rose[1xSmith, H.V. and Rose, J.B. Parasitol. Today. 1998; 14: 14–22Abstract | Full Text | Full Text PDF | PubMed | Scopus (180)See all References[1]reported that education is a better deterrent than legislation for the prevention of waterborne outbreaks. I disagree. The production of meat and dairy products has reached an industrial scale. I do not believe that education alone will be sufficient to convince industry that they are mainly responsible for the contamination of the environment with Cryptosporidium oocysts. Legislation will be required.