Molecular epidemiological investigations of Enterocytozoon bieneusi
AffiliationVeterinary and Agricultural Sciences Collected Works
Document TypePhD thesis
Access StatusThis item is embargoed and will be available on 2021-10-08.
© 2019 Yan Zhang
Enterocytozoon bieneusi is a microsporidian microorganism that causes intestinal disease in animals including humans. Although E. bieneusi has been discovered and investigated in numerous countries around the world, at the commencement of this PhD project, there was no record of E. bieneusi in animals in Australia and no information on the prevalence and genetic make-up of E. bieneusi populations in this country. Thus, the present project explored E. bieneusi of a number of species of wild and domestic animals as well as humans in parts of Australia using a molecular approach, in order to improve our knowledge of the epidemiology of this microsporidian. Nested-PCR-based sequencing of the internal transcribed spacer (ITS) and/or small subunit (SSU) of nuclear ribosomal DNA was used for the detection of E. bieneusi DNA in faecal samples and the genotypic characterisation of this microbe. In the first instance, three species of wild deer (Cervus elaphus, Dama dama and Rusa unicolor; n = 610) and three species of wild marsupials (Macropus giganteus, Vombatus ursinus and Wallabia bicolor; n = 1365) in Melbourne's water catchment areas were investigated (Chapters 2 and 3). Here, E. bieneusi was detected in 4.1% of sambar deer and 1.4% of marsupials. Phylogenetic analyses of sequence data showed that genotypes D, J, MWC_d1, MWC_d2 and Type IV (in sambar deer) and MWC_m1 and NCF2 (in marsupials) clustered with E. bieneusi genotypes recorded previously in humans, indicating the zoonotic potential of these genotypes. Studies of cattle on farms located near Tarago reservoir (n = 471; Chapter 4) in Victoria, and alpacas in the states of New South Wales, Queensland, South Australia, Victoria and Western Australia (n = 81; Chapter 5) revealed relatively high prevalences of E. bieneusi in both cattle (10.4%) and alpacas (9.9%). The phylogenetic analysis of ITS sequence data revealed six genotypes (BEB4, I and J, TAR_fc1, TAR_fc2 and TAR_fc3) in cattle and three (ALP1, APL3 and P) in alpacas, all recognised to have zoonotic potential, indicating that these herbivores might act as reservoirs for human infection. Subsequently, a study of companion animals (cats and dogs; n = 514) identified genotype D, which is commonly detected in humans (Chapter 6). However, surprisingly, an investigation of humans (n = 605) in the states of Queensland and Western Australia (Chapter 7) did not identify the genotypes previously found in cats, dogs and wildlife in the state of Victoria, although, surprisingly, a known genotype (i.e., ALP1) recorded in farmed alpacas (Chapter 5) was identified in humans for the first time (Chapter 7). This latter finding raises questions about the transmissibility of this genotype from alpaca to humans. Overall, this thesis has recorded E. bieneusi, for the first time, in a variety of animals in Australia, and provides a first glimpse of the epidemiology of this microsporidian in this country (Chapter 8). The findings of this thesis indicate that the animals studied here, including eastern grey kangaroos, swamp wallabies and wombats; sambar deer, cattle and alpacas; and cats and dogs, can all carry E. bieneusi genotypes that might infect humans via water, food and/or the environment. To provide further evidence to support this proposal and much deeper insights, well-designed large-scale (temporal and spatial) epidemiological studies are required. Population genomics of E. bieneusi using advanced next-generation sequencing and informatics tools could significantly support this endeavour. Other future investigations might also, for example, attempt to establish in vitro culture and in vivo systems for E. bieneusi for controlled studies of the biology of distinct genotypes of this microbe as well as approaches for assessing the viability and infectivity of E. bieneusi and anti-infectives against this microbe. Clearly, we are only beginning to understand some aspects of this enigmatic pathogen - E. bieneusi.
Keywordsalpaca; Australia; cat; cattle; Common wombat; dog; Eastern grey kangaroo; Enterocytozoon bieneusi; Fallow deer; genotype; human; internal transcribe spacer (ITS) of nuclear ribosomal DNA; phylogenetic analysis; prevalence; Red deer; risk factor; Sambar deer; Swamp wallaby
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