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Title: An investigation of giardiasis and cryptosporidiosis in Malawi and Cambodia
Author: Nuchjangreed, C.
ISNI:       0000 0004 7428 6179
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2018
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The parasites Giardia duodenalis and Cryptosporidium spp., which infect a broad range of vertebrates, are major causes of diarrhoeal disease in humans worldwide. The aim of this thesis was to understand the zoonotic transmission potential of Giardiasis and Cryptosporidiosis in children in Malawi and Cambodia using molecular epidemiological tools. The pattern of faecal Volatile Organic Compounds (VOCs) from children with Cryptosporidiosis in Malawi was also examined. In Chapter 2, faecal samples collected from children under 5 years of age with diarrhoea, living in diverse geographical regions in Malawi, were screened for both parasites microscopically using the Direct Fluorescence Assay (DFA). Nested PCR was used for subtyping Giardia (the bg, tpi and gdh genes) and Cryptosporidium spp. (SSU-rRNA and GP60 genes). The prevalence of G. duodenalis (11.4%,15/132) was significantly lower than the prevalence of Cryptosporidium spp. (23.5%, 31/132) by DFA. In contrast, the prevalence of G. duodenalis (28%,56/200) was significantly higher than the prevalence of Cryptosporidium spp. (11%, 22/200) by nested PCR. Mixed infections with both Giardia assemblage A and B were predominant. The predominance of C. hominis indicated that the anthroponotic route plays a major role of Cryptosporidium transmission in Malawi. In Chapter 3, the prevalence and identity of G. duodenalis assemblages among isolates from children in Cambodia was investigated. Both assemblages A and B were common in Cambodia, however, assemblage B was the most predominant. These data indicate that anthroponotic routes play a major role in Giardia transmission in Cambodia. Nevertheless, Giardia parasites of assemblage B demonstrated higher genetic variation than the other assemblages. Because the major transmission route of Giardia is likely anthroponotic, public health policies should focus on improvements in sanitation and hygiene rather than changes in animal/meat processing. In Chapter 4, I determined genetic variation among Giardia isolates from Malawi and Cambodia. A multiple alignment was performed and phylogenetic trees were generated. The data demonstrated that Giardia assemblage A and B were prevalent in children in both countries, with a predominance of assemblage B. These findings suggest that anthroponotic transmission could be a dominant transmission route for giardiasis in both countries. In Chapter 5, I studied stool samples from patients with confirmed Cryptosporidium infection and negative controls. I tested the hypothesis that the pattern of excreted VOCs could be specific to certain types of diarrhoeal infection. The abundance of several VOCs were significantly different in the two groups; cyclopentane and 3-hydroxy-2-butanone were associated with Cryptosporidium positive samples, and 1-propanol with negative control samples. The presence of cyclopentane and 3-hydroxy-2-butanone and the absence of 1-propanol in Cryptosporidium positive faecal samples could form the basis of a diagnostic test. In Conclusion, my findings suggest that G. duodenalis assemblage B was the predominant assemblage in Malawi and Cambodia. C. hominis was the predominant species in Malawi. Both parasites likely undergo predominantly anthroponotic transmission in these populations. Public health measures targeted at hand washing, improving sanitation, and providing clean drinking water are important strategies for the control of Giardiasis and Cryptosporidiosis infection in these countries.
Supervisor: Cunliffe, Nigel ; Wastling, Jonathan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral