My introduction to the fascinating world of parasites and Fasciola was accidental, or rather, a fluke! I met Professor John Dalton, the lead of the Molecular Parasitology Laboratory, and Editorial Board member of Parasitology, while working on a drug metabolism and hepatotoxicity project using HepG2 cell-derived spheroids at the Department of Pharmacology and Therapeutics at the University of Galway. After several hours of parasite chat, I was hooked and embarked on a PhD migratory pathway!

Helminth parasites infect around 2 billion people worldwide. Our prime parasite model, the liver fluke, Fasciola hepatica, infects 17 million people worldwide, with 180 million at risk of infection. The parasitic worm, which has the widest geographical distribution of any worm, infects various mammalian hosts, including livestock, such as cattle, sheep, goats, and water buffalo, causing annual losses of €2.5 billion to livestock and food industries. With the rise of drug-resistant strains, the discovery and development of novel treatments are urgently needed. The parasite is particularly important to Irish agriculture as it infects 85% of cows and 45% of sheep here. Infection with the liver fluke occurs upon the ingestion of the encysted metacercariae, typically found on vegetation (grass). Shortly afterwards, the parasites excyst in the duodenum, cross the intestinal wall, and migrate to the liver. For the next 6-8 weeks, the Newly Excysted Juveniles (NEJs) tunnel through and feed on the liver, resulting in haemorrhaging, tissue damage, inflammation, and fibrosis, until reaching the bile ducts where they mature. The NEJs are microscopic – around a sixth of a millimetre – growing rapidly (>1000 times) as they feed and burrow through the liver tissue.

My PhD project focuses on this early infective and migratory stage of the parasite. Due to their microscopic size, it is difficult to study the NEJs in vivo. An in vitro system is urgently needed to study their developmental biology, host-pathogen interactions, and invasion that will allow the development of new vaccines that prevent infection and the pathology caused by the migrating parasites in the liver. 

Spheroids are three-dimensional cell aggregates, replicating the physiological conditions of in vivo tissue much closer than a monolayer of cells. HepG2 is a human cancer cell line which exhibits key characteristics of primary hepatocytes. HepG2 spheroids are widely used in the pharmaceutical industry for pre-clinical drug metabolism and hepatotoxicity studies. In our case, HepG2 spheroids create a solid tissue-like ‘mini-liver’ in a cell culture well, allowing for investigations into the growth and development of the invasive stages of the NEJ, as well as parasite-host interactions.

NEJs grown in the presence of HepG2 spheroids significantly increase in size. Moreover, the development of the tegument and other structures, such as sensory organs, is greatly enhanced. During the first several days, the parasites exhibit invasion/migration-like behaviour, burrowing through and crawling around the periphery of the spheroids. Furthermore, using fluorescently labelled spheroids, we observed parasites actively feeding on and ingesting the HepG2 cells, which we believe stimulates the parasites’ growth.

We expect that our in vitro spheroid-parasite system will avoid or reduce the need to use laboratory animals and, therefore, comply with the 3R principles of replacement, reduction, and refinement of animal use in research. We are aiming to integrate this in vitro platform into our search for vaccine candidates and novel biotherapeutics. Our next step is to benchmark our in vitro-grown worms to known in vivo molecular and genomic data and assess the model’s potential in the developmental studies of other parasitic helminths in vitro.

Parasitology, published by Cambridge University Press, sponsors the Irish Society for Parasitology William C. Campbell Award every year.

About Parasitology

Parasitology is an important specialist journal covering the latest advances in the subject. It publishes original research and review papers on all aspects of parasitology and host-parasite relationships, including the latest discoveries in parasite biochemistry, molecular biology and genetics, ecology and epidemiology in the context of the biological, medical and veterinary sciences.