Molecular epidemiology of Giardia duodenalis in the high-income world

Krumrie, Sarah (2022) Molecular epidemiology of Giardia duodenalis in the high-income world. MVM(R) thesis, University of Glasgow.

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Giardia duodenalis is a gastrointestinal parasite that infects most mammals, including humans. Outcome of infection ranges from asymptomatic carriage to severe clinical disease, leading to digestive abnormalities lasting years beyond infection. In high-income countries, this parasite was once primarily thought to be contracted by individuals with a history of foreign travel. Recent evidence suggests that endemic infection is an important factor in the epidemiology of giardiasis, and consequently human patients without a history of travel should be screened for Giardia to aid in the understanding of endemic infection.

The first objective of the present study was to undertake a literature review of human giardiasis outbreaks to determine the primary routes of transmission in high-income countries. Outbreaks were categorised by transmission route, which included waterborne, foodborne, travel, person-to-person, zoonotic and direct faecal exposure. Waterborne transmission emerged as the route associated with the highest number of outbreak studies, followed by person-to-person transmission. This review highlighted the need for increased screening protocols in high-income countries and investigation into transmission routes other than travel.

Being able to discern between different sub-types of Giardia, termed assemblages, is an important aspect of transmission analysis since different assemblages show varying levels of host-specificity, with some capable of infecting both humans and animals. Current Giardia typing methods rely largely on PCR of marker loci and sequencing of amplicons, however these suffer from poor amplification success rates particularly when applied to non-human assemblages. In this study, recently published genomic data was used to modify and optimise one such Giardia marker to increase sensitivity. Using this improved marker, the success rate across multiple assemblages increased markedly and it was subsequently applied to type a large collection of UK human and companion animal field samples. This revealed an appreciable presence of zoonotic assemblages in the companion animal population and highlighted them as potential source of human infection. This study adds to the knowledge on Giardia epidemiology in the context of a high-income country and provides improved genotyping methodology which can be applied to future studies.

Item Type: Thesis (MVM(R))
Qualification Level: Masters
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
Supervisor's Name: Weir, Professor William and Capewell, Dr. Paul
Date of Award: 2022
Depositing User: Theses Team
Unique ID: glathesis:2022-83312
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 20 Dec 2022 11:34
Last Modified: 21 Dec 2022 14:46
Thesis DOI: 10.5525/gla.thesis.83312
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