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Innovative approaches to understanding and limiting the public health risks of Cryptosporidium in animals in Australian drinking water catchments

Zahedi, AlirezaORCID: 0000-0002-0165-3797 (2018) Innovative approaches to understanding and limiting the public health risks of Cryptosporidium in animals in Australian drinking water catchments. PhD thesis, Murdoch University.

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Cryptosporidium is the most important waterborne pathogen due to its resistance to chlorine in drinking water. The contribution of Cryptosporidium to waterborne diseases in Australia is however, unknown. The level of faecal contamination of drinking water catchments with this parasite was assessed by longitudinal analysis of faecal samples collected from marsupials, sheep, cattle and rabbits (n = 5,774) from eleven drinking water catchments across three states; New South Wales (NSW), Queensland (QLD) and Western Australia (WA). Faecal samples were screened by quantitative PCR (qPCR) and typed at two loci using Sanger sequencing. The overall prevalence of Cryptosporidium in faecal samples was 18.3% (1,054/5,774; 95% CI, 17.3-19.3). Of these, 873 samples produced clean Sanger sequencing chromatograms, and the remaining 181 samples, which initially produced chromatograms suggesting the presence of multiple different sequences, were re-analysed by Next Generation Sequencing (NGS) to resolve the presence of Cryptosporidium and the species composition of mixed infections. The overall prevalence of mixed infection was 1.7% (98/5,774), and in the remaining 83 samples, NGS detected only one species of Cryptosporidium. Of the 17 Cryptosporidium species and four genotypes detected (Sanger sequencing combined with NGS), 13 are capable of infecting humans; C. parvum, C. hominis, C. ubiquitum, C. cuniculus, C. meleagridis, C. canis, C. felis, C. muris, C. suis, C. scrofarum, C. bovis, C. erinacei and C. fayeri. Sewage (influent) samples across these states were also collected (n = 730) and screened by qPCR and typed using next generation sequencing (NGS). In sewage samples, the overall Cryptosporidium prevalence was 11.4% (83/730); 14.3% (3/21) in NSW, 10.8% (51/470); in QLD and 12.1% (29/239) in WA, and a total of 17 Cryptosporidium species and 6 genotypes were detected by NGS, including some of the same zoonotic species detected in animal faecal samples. This study highlights the public health importance of continued identification of the sources/carriers of human pathogenic strains for accurate risk assessment and optimal catchment management.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Supervisor(s): Ryan, Una, Robertson, Ian and Oskam, Charlotte
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