The development of the rumen fluke, Calicophoron daubneyi, within the mammalian host

  • Nicky Oliver

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

Paramphistomosis, caused by the rumen fluke, Calicophoron daubneyi, is an emerging parasitic infection of ruminants in the UK/Ireland. Despite its prevalence, little is known about the development of this species and its interaction with the ruminant host. Thus, the major aim of this project was to investigate the development of C. daubneyi, at both morphological and molecular levels, to answer some basic questions about its biology and interactions with its ruminant host. Accordingly, four major intra-mammalian developmental stages were studied; the newly-excysted juveniles (NEJ) and immature flukes that reside in the duodenum and the newly-migrated and adult flukes that are found in the rumen. Firstly, whole mount preparations and histological examination of these developmental stages revealed the gross structure and timing of development of the reproductive organs with the male structures (i.e. anterior and posterior testes) appearing as genital anlagen as early as the immature fluke stage within the duodenum. In contrast, the female structures, including the ovary and vitellaria do not appear until the flukes have arrived in the rumen. The four developmental stages were also observed at the ultrastructural level, with a focus on the tegument, digestive system, excretory system and reproductive structures. The fine structure of the tegument suggests its major role is protection since it lacks mitochondria and thus may not participate in active uptake of molecules from the host environment. The gastrodermal cells that line the C. daubneyi gut are a source of antigenic molecules, particularly during the early stages of infection, and have unique structural adaptations (such as particularly long and dense lamellae), which provide insight into the feeding strategies used by the fluke. Overall, the fine structure of the reproductive system reflects that of other trematode species. However, microscopical observations, and interrogation of transcriptome resources, suggest that C. daubneyi lacks tyrosinase, the enzyme used by other trematode species to form di-tyrosine crosslinks between eggshell precursor proteins during eggshell formation. Comparative sequence analysis revealed that a number of conserved tyrosines known to be crosslinked in other species have been replaced by cysteines in C. daubneyi eggshell precursor proteins suggesting that rumen fluke use different crosslinking chemistry (potentially disulphide linkages) during the final stages of eggshell formation. Mass spectrometry analysis of C. daubneyi eggshell protein extracts identified pro-resilin, a protein with elastic properties not previously reported in trematode eggshells. C. daubneyi eggs were found to be more resistant to changes in pH and hypochlorite concentrations than Fasciola hepatica eggs suggesting that their atypical eggshell composition/crosslinking biochemistry may confer
additional structural stability in changing environmental conditions. The findings described here provide a framework for detailed studies of C. daubneyi development at the molecular level and will aid in the development of new diagnostic tools and vaccine candidates, which are currently lacking for this species.
Date of AwardDec 2021
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsNorthern Ireland Department for the Economy
SupervisorMark Robinson (Supervisor), Geoffrey Gobert (Supervisor) & Aurelie Aubry (Supervisor)

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