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Investigating the transmission dynamics of pig parasites within small holder farming communities in Lao PDR

Peck, Ashleigh Mary (2021) Investigating the transmission dynamics of pig parasites within small holder farming communities in Lao PDR. Honours thesis, Murdoch University.

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Soil-transmitted helminths (STHs) are considered neglected tropical diseases (NTD) that infect 1.5 billion people worldwide. STHs are highly prevalent in subtropical and tropical environments, especially in South East Asia. In areas where humans live in sympatry with animals, (e.g pigs and dogs), the potential for cross-transmission between hosts is high, especially in communities with free-roaming pigs and dogs, and limited water access, sanitation, and hygiene (WASH). A previous study in Northern Lao PDR identified a high prevalence of polyparasitism in all host types warranting an investigation into the transmission dynamics within this study site. To achieve this, molecular characterization of the highly prevalent STHs Ascaris spp. and Trichuris spp. was completed to identify patterns of cross-transmission and potential hybridization.

158 faecal samples from humans, pigs, and dogs were collected in 2013 and the prevalence of parasite infections was analysed by microscopy. Based on microscopic results, 36 faecal samples positive for Ascaris spp. and Trichuris spp. were chosen for molecular characterisation at the cox1 and ITS gene regions. New primers for the 18s gene region were developed for Trichuris spp. identification.

Of the 36 faecal samples extracted, 19 produced positive results for the Ascaris cox1 gene region. Phylogenetic analysis of the Ascaris cox1 sequences identified 3 clusters with human, pig, and dog samples grouping together. The 18s primers produced positive results for a Trichuris vulpis worm extraction, whilst the dog parasite Spirocerca vulpis was amplified in a human and a dog faecal sample.

Phylogenetic analysis demonstrated that humans, pigs, and dogs share the same Ascaris genotypes, which is indicative of recent or current cross-transmission. Potential hybrid species were identified by sequencing analysis and supported by phylogenetic relationships which indicate that introgression between Ascaris genotypes has or is currently occurring. This finding is likely a result of sympatric living conditions of humans, pigs, and dogs which facilitate parasite cross-transmission. This was further supported by evidence of Spirocerca vulpis, a dog parasite, detected in a human sample. These results advocate for the improvement of WASH and emphasise the involvement that pigs and dogs have on the transmission dynamics of human parasite infections.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): Veterinary Medicine
Supervisor(s): Ash, Amanda
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