Enumeration and Dissemination of Cryptosporidium in Ontario Surface Waters

Cryptosporidium is a waterborne protozoan pathogen which has been gaining increasing attention as a causative agent of gastro-intestinal illnesses in humans. Its ability to survive extended periods of time in the water and its resistance to chemical disinfection has made it a difficult organism to deal with in terms of water treatment. The objective of this thesis was to determine concentrations of Cryptosporidium in Ontario surface waters, look for the impact of particle attachment on Cryptosporidium, and determine the efficacy of UV disinfection on oocysts. The raw water intakes of eight drinking water treatment plants across Ontario were surveyed for two years to determine the bacterial and oocyst levels. USEPA Method 1623 was used to analyze the samples for the presence of Cryptosporidium oocysts. A total of 81 samples were taken, 60% of which were positive for oocysts, with an average of 2.7±4.8 oocysts per 100 L across all eight plants. A significant (p<0.01) correlation between rainfall and oocyst’s presence was found. Particle association tests were then performed on stool-isolated oocysts. Cryptosporidium parvum oocysts were found to have more affinity for inorganic sediment species versus organic types. Natural sediment samples from around Ontario showed a similar trend, where a significant (p<0.01) negative correlation was found between oocyst adsorption and organic content. Cryptosporidium parvum oocysts were found to be protected from UV irradiation by wastewater particles. Consequently when the particles were reduced in size by kaolin, the UV irradiation process regained its efficiency. The knowledge gained in this study has helped to fill a few gaps in the information present on Cryptosporidium and allowed us to postulate a model of oocyst transmission in the environment.