SURVEY OF LOCH LOMOND TO ASSESS THE OCCURRENCE AND PREVALENCE OF CRYPTOSPORIDIUM SPP. OOCYSTS AND THEIR LIKELY IMPACT ON HUMAN HEALTH
Report No FR0409
J F W Parker*+ H V Smith* and R W A Girdwood*
* Scottish Parasite Diagnostic Laboratory, Stobhill General Hospital, + Environmental Health Division, University of Strathclyde
To assess the occurrence of Cryptosporidium spp. oocysts entering water treatment by long term sampling of water at the abstraction point at Ross Priory.
To assess the occurrence of cryptosporidiosis in both humans and animals in the Lomond southern catchment area and in Lomond water distribution network.
To attempt to determine the sources of oocysts penetrating the aquatic environment in the Lomond southern catchment area and to assess the viability of waterborne oocysts detected.
To attempt to assess the input of oocysts from avian and piscine species resident in the catchment of the loch.
The report of the Group of Experts on Cryptosporidium in Water* recommended that a survey of occurrence in source waters should be carried out. A survey of lowland surface waters and boreholes has been completed and reported elsewhere. This study extended the survey to an upland water and included an analysis of epidemiological and environmental information in the water distribution areas.
The source of contamination of water with oocysts is not known. By investigating potential sources of contamination, such as sewage effluent and slurry and muck from livestock, a picture of the source and fate of oocysts can be built up. The impact on health in the population supplied with Loch Lomond water can also be monitored because, in Scotland cryptosporidiosis is a reportable disease and such information is available from laboratory sources and the Environmental Health (Scotland) Unit.
By constant monitoring of water at the abstraction point oocysts entering water treatment could be detected. This provided a basis for monitoring water in the distribution network.
Information available on cryptosporidiosis in the communities served by Lomond water indicated that the small numbers of oocysts detected in both raw and final water could not be correlated with any identifiable outbreak of waterborne disease. The majority of oocysts detected at the abstraction point were non-viable. Viable oocysts were detected in April and May (20 - 40% of those detected were viable), coinciding with the detection of large numbers of viable oocysts in faecal samples from scouring calves in the Lomond southern catchment area.
Oocysts were detected in both human sewage effluent and bovine faecal specimens, implicating both as a source of contamination of tributaries to the loch. Oocysts were not detected from other agricultural and animal material tested.
Continuous sampling of water for abstraction should be continued. This would provide an early warning to water authorities in the event of oocysts (possibly at high concentrations) being detected. Further and more intense work should be undertaken on ascertaining the disease status of the animal population and on the farming practices with cooperation from farmers and veterinarians, to form a more comprehensive picture of areas of potential contamination.
The unique monitoring situation set up, together with the level of interaction already achieved with the Environmental Health (Scotland) Unit and the Communicable Diseases Surveillance Unit throughout this project could be further used to expand the knowledge of Cryptosporidia in water and the environment.
V RESUME OF CONTENTS
This final report on a survey of Loch Lomond reports the levels of oocysts in an upland and the treated water over a two year period. The occurrence of the disease in humans and cattle has been monitored and the impact upon the source water by contamination from land runoff or sewage effluent assessed.
* DoE/DH (1990) Cryptosporidium in water supplies. Report of the Group of experts. Chairman: Sir John Badenoch. London HMSO. Department of the Environment, Department of Health.
Copies of the Report are available from FWR, price £15.00 less 20% to FWR Members