- Email: [email protected]
Waterborne Cryptosporidiosis and the Need for Legislation
Letters Waterborne Cryptosporidiosis and the Need for Legislation In the January issue of Parasitology Today, Smith and Rose1 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 hosts2. A recent study3 on the prevalence of cryptosporidiosis in calves in the 12 agricultural regions of the Province of Québec, 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 countries4. 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.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 countries1. Several factors could explain this low percentage of positivity in Canadian water4: (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
Reply Dr Faubert raises many interesting points regarding the significance of the zoonotic route of transmission and the need for legislation. We agree that prevalence of neonatal bovine cryptosporidiosis can be high, and have reported findings similar to his in our investigations of neonatal and adult bovine Cryptosporidium infections in the west of Scotland1–3. The spreading of oocyst-contaminated farmyard manure (FYM) can augment the numbers of oocysts that may eventually reach water courses and the spraying of oocyst-contaminated slurry was implicated in the Ayrshire, UK, outbreak of waterborne cryptosporidiosis4. Since only viable oocysts are potentially infectious, mechanisms that reduce oocyst viability prior to the application of FYM onto land have practical significance. In experimentally infected lambs, oocyst viability declined during the second week of oocyst excretion and, of the total number of oocysts excreted (~5 x109), approximately 50% were not viable5. We speculated that a specific or non-specific immunological mechanism caused this reduction in oocyst viability. Our ‘on farm’ survey of oocyst contamination and viability indicated that a Parasitology Today, vol. 14, no. 12, 1998
proportion of oocysts could be rendered non-viable in calf pens by allowing urine to admix with oocyst-contaminated faeces in an absorbent matrix of straw, which also reduced leaching of viable oocysts into farm drains6. Furthermore, effective composting of oocyst-contaminated FYM reduces the number of viable oocysts released into the environment. Our data indicate that the mean viability of oocysts present in composted FYM was 13.2% (range 0–57.1%), the addition of fresh manure onto an existing midden increased, temporarily, the numbers of viable oocysts in the midden6. Adoption of such practices by the livestock industry, while not completely removing the potential for contamination of watercourses with viable oocysts, significantly reduces potential threat. Such information can be used to generate effective Hazard Assessment Critical Control Point (HACCP) programmes. While, in the above settings, oocyst survival can be reduced by interventions identified in Codes of Good Practice, the survival of oocysts excreted by livestock on pasture and by feral animals is dependent upon the microclimate they occupy, with
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 Québec alone) – a fair potential for contamination not only of surface water, but of humans and wildlife as well. In their review, Smith and Rose1 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. References 1 Smith, H.V. and Rose, J.B. (1998) Parasitol. Today 14, 14–22 2 Esteban, J.G. et al. (1998) Am. J. Trop. Med. Hyg. 58, 50–55 3 Ruest, N. et al. Can. Vet. J. (in press) 4 Fayer, R. and Ungar, B.L.P. (1986) Microbiol. Reviews 50, 458–483 5 Wallis, P. et al. (1996) Appl. Env. Microbiol. 62, 2789–2797 Gaétan Faubert Institute of Parasitology, McGill University Montréal, Québec, Canada
the moist, cool microclimates of temperate regions, such as Canada and Scotland, likely to support their prolonged survival. Viable oocysts that gain rapid access into aquatic environments (eg. from the daily washing down of livestock pens, milking parlours, abbatoirs, etc. as well as those released with sewage effluent) are, in our opinion, the most likely to be infectious to other susceptible hosts. Indeed, such oocysts may have been responsible for some of the five documented waterborne outbreaks of cryptosporidiosis in Canada (W. Robertson, pers. commun.). Clearly, a better understanding of the viability as well as a better control of oocysts discharged from point sources such as farm drains (as well as abattoir and livestock market effluents and sewage treatment works) and non-point sources is warranted if we are to move to a watershed-based assessment and protection. Sustainability of water resources can be promoted by awareness, education and partnership initiatives as well as by legislation. Codes of Practice already exist for the protection of water sources, which aim to protect public health and water quality, as do Codes for avoiding water pollution from agricultural activity. Cryptosporidium could be readily included into such Codes of Practice.
0169-4758/98/$ – see front matter © 1998 Elsevier Science. All rights reserved.
501
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.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 countries1. Several factors could explain this low percentage of positivity in Canadian water4: (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
Reply Dr Faubert raises many interesting points regarding the significance of the zoonotic route of transmission and the need for legislation. We agree that prevalence of neonatal bovine cryptosporidiosis can be high, and have reported findings similar to his in our investigations of neonatal and adult bovine Cryptosporidium infections in the west of Scotland1–3. The spreading of oocyst-contaminated farmyard manure (FYM) can augment the numbers of oocysts that may eventually reach water courses and the spraying of oocyst-contaminated slurry was implicated in the Ayrshire, UK, outbreak of waterborne cryptosporidiosis4. Since only viable oocysts are potentially infectious, mechanisms that reduce oocyst viability prior to the application of FYM onto land have practical significance. In experimentally infected lambs, oocyst viability declined during the second week of oocyst excretion and, of the total number of oocysts excreted (~5 x109), approximately 50% were not viable5. We speculated that a specific or non-specific immunological mechanism caused this reduction in oocyst viability. Our ‘on farm’ survey of oocyst contamination and viability indicated that a Parasitology Today, vol. 14, no. 12, 1998
proportion of oocysts could be rendered non-viable in calf pens by allowing urine to admix with oocyst-contaminated faeces in an absorbent matrix of straw, which also reduced leaching of viable oocysts into farm drains6. Furthermore, effective composting of oocyst-contaminated FYM reduces the number of viable oocysts released into the environment. Our data indicate that the mean viability of oocysts present in composted FYM was 13.2% (range 0–57.1%), the addition of fresh manure onto an existing midden increased, temporarily, the numbers of viable oocysts in the midden6. Adoption of such practices by the livestock industry, while not completely removing the potential for contamination of watercourses with viable oocysts, significantly reduces potential threat. Such information can be used to generate effective Hazard Assessment Critical Control Point (HACCP) programmes. While, in the above settings, oocyst survival can be reduced by interventions identified in Codes of Good Practice, the survival of oocysts excreted by livestock on pasture and by feral animals is dependent upon the microclimate they occupy, with
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 Québec alone) – a fair potential for contamination not only of surface water, but of humans and wildlife as well. In their review, Smith and Rose1 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. References 1 Smith, H.V. and Rose, J.B. (1998) Parasitol. Today 14, 14–22 2 Esteban, J.G. et al. (1998) Am. J. Trop. Med. Hyg. 58, 50–55 3 Ruest, N. et al. Can. Vet. J. (in press) 4 Fayer, R. and Ungar, B.L.P. (1986) Microbiol. Reviews 50, 458–483 5 Wallis, P. et al. (1996) Appl. Env. Microbiol. 62, 2789–2797 Gaétan Faubert Institute of Parasitology, McGill University Montréal, Québec, Canada
the moist, cool microclimates of temperate regions, such as Canada and Scotland, likely to support their prolonged survival. Viable oocysts that gain rapid access into aquatic environments (eg. from the daily washing down of livestock pens, milking parlours, abbatoirs, etc. as well as those released with sewage effluent) are, in our opinion, the most likely to be infectious to other susceptible hosts. Indeed, such oocysts may have been responsible for some of the five documented waterborne outbreaks of cryptosporidiosis in Canada (W. Robertson, pers. commun.). Clearly, a better understanding of the viability as well as a better control of oocysts discharged from point sources such as farm drains (as well as abattoir and livestock market effluents and sewage treatment works) and non-point sources is warranted if we are to move to a watershed-based assessment and protection. Sustainability of water resources can be promoted by awareness, education and partnership initiatives as well as by legislation. Codes of Practice already exist for the protection of water sources, which aim to protect public health and water quality, as do Codes for avoiding water pollution from agricultural activity. Cryptosporidium could be readily included into such Codes of Practice.
0169-4758/98/$ – see front matter © 1998 Elsevier Science. All rights reserved.
501