Exploiting stem cell biology for liver fluke control

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Liver fluke (Fasciola species) are flatworm parasites that infect diverse mammals including humans and ruminant livestock such as cattle, goats and sheep. In humans, the parasite causes the disease fascioliasis which is a neglected tropical disease with an estimated 17 million people believed to be infected. The worm impacts global food security as it undermines the health and productivity of livestock in which it causes fasciolosis, estimated to cause losses of ~$US3 billion/year worldwide. Major concerns are that: the Animal and Plant Health Agency list liver fluke as the most commonly diagnosed helminth parasite of sheep and cattle in UK; recent estimates of changing prevalence in the UK have forecast unprecedented levels of fasciolosis risk by 2050; farmers rely on the administration of drugs which are becoming less effective due to drug resistance. Adult worms live in the bile ducts and juveniles occur encysted on vegetation; after being swallowed the juveniles excyst and migrate from the intestine through the liver to the bile ducts. The juvenile worm is the key pathogen, causing profound damage to the liver as it moves from the intestine to the bile duct. It is this stage that can kill lambs and sheep and the stage against which there is only one effective drug, triclabendazole (TCBZ). Critically, TCBZ-resistance threatens the sustainability of livestock farming in many regions of the world such that new flukicides and/or a vaccine are needed. Key impediments to research studies on liver fluke have included the lack of good genomic resources, the absence of a model system for functional studies and the reliance on host animal-based in vivo experiments to inform fluke biology. The new bioinformatic resources as well as the ability to culture the juvenile fluke in the laboratory outside of a host, mean that experiments on fluke developmental biology are now possible, stimulating this project. Our ability to culture growing juveniles, for sustained timeframes, and to selectively disrupt gene targets provides an opportunity to transform approaches to liver fluke biology and the discovery of new drug targets. We have found that liver fluke stem cells are critical to their growth and development and as such, are an appealing resource for new drug targets. Whilst the critical role played by stem cells in chemotherapy and drug resistance is established in the cancer field, their role in parasite-drug interactions and potential exploitation in parasite control have not been investigated. Our preliminary data expose a critical role for these stem cells in liver fluke growth and indicate that they play a role in parasite-drug interaction, encouraging their exploitation for the discovery of new drug targets. In this project, supported by an industrial partner, we propose to discover key genes involved in liver fluke stem cell biology and to evaluate their potential as novel drug targets for new flukicides. To do this we propose to generate new bioinformatics resources on the genes expressed in juvenile liver fluke stem cells. We will also evaluate the importance of stem cells to parasite-drug interactions to help inform their role in how liver fluke parasites tolerate/recover from drug exposure. We will study the relationships between parasite drug sensitivities and stem cell biology and the consequences of disrupting liver fluke stem cells on parasite responses to drug treatments. Finally, we will evaluate a sub-set of liver fluke stem cell genes for their potential as new drug targets using the functional genomics tools we have established. Prioritized and validated targets will be entered into new drug screens by our industrial collaborator to initiate the discovery of new drugs to control liver fluke. The approaches taken here have direct relevance to liver fluke and indirect relevance to other parasitic worms that cause a diverse range of important diseases of animals and humans.