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Molecular epidemiology of Giardia spp. in different hosts and watersheds Prystajecky, Natalie Anne


Giardia lamblia has been problematic in British Columbia (BC) since the 1980s, having been the etiological agent in 13 of the 29 documented waterborne outbreaks in the province. Despite improvements to drinking water facilities, giardiasis continues to occur at higher rates in BC compared to the rest of Canada. This study aimed to address knowledge gaps with regard to the occurrence and molecular epidemiology of Giardia isolates, to help address the higher occurrence of giardiasis in British Columbia. This study was conducted in three steps. First, tools were developed and validated to genotype G.lamblia isolates into groups/genotypes called Assemblages. These tools were first applied to a library of archived G.lamblia isolates collected from patients, animals and water sources in British Columbia. These same tools were then applied to water samples collected in the Salmon River watershed in the Township of Langley, BC, the second stage of the study. The occurrence and characteristics of isolates collected in the Salmon River were then compared to isolates collected in the Grand River watershed, an intensely developed mixed-urban watershed in Ontario, for the third stage of the study. In the first study, it was determined that 18s rRNA nested PCR with sequencing was the most appropriate molecular epidemiological tools to study G.lamblia in water supplies. Using a combination of molecular methods and USEPA Method 1623, it was determined that the majority of isolates in the Salmon River watershed were potentially infectious to humans (belonging to Assemblages A and B), with Assemblage A occurring most frequently. In contrast, Assemblage B was the most frequently detected genotype in the Grand River watershed, a more intensely developed watershed. Analysis of rainfall and sequence data suggests that G.lamblia isolates could have originated from sewage effluent or septic tanks, which was confirmed with the occurrence of Cryptosporidium hominis. Non-zoonotic G.lamblia isolates occurred more frequently in the Grand River watershed than in the Salmon River watershed but this water source still represents a threat to public health. Although challenging to incorporate molecular analyses into environmental monitoring, suggestions are made for the most effective linking of molecular analyses into Method 1623.

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