Abstract
The parasitic nematode Trichuris trichiura is a significant burden on public health in developing countries, and currently available drugs exhibit a poor cure rate. Worms live within a specialised tunnel of host intestinal epithelial cells and have anterior-ventral projections of the cuticle termed “cuticular inflations”, which are thought to be involved in host-parasite interactions. This work aimed to characterise structure and suggest a function of cuticular inflations in the most tractable and widely-used model of trichuriasis, Trichuris muris. Using scanning electron microscopy, we show for the first time that most cuticular inflations develop between the second and third larval moults. Correlative X-ray computed tomography (CT)-steered Serial Block Face Scanning Electron Microscopy (SBF-SEM) and transmission electron microscopy enabled ultrastructural imaging of cuticular inflations, and showed the presence of an additional, web-like layer of cuticle between the median and cortical layers of the inflation. Additionally, we characterised variation in inflation morphology, resolving debate as to the inflations’ true shape in situ. Cells underlying the inflations had many mitochondria, and we highlight their potential capacity for active transport as an area for future investigation. Overall, insights from the powerful imaging techniques used provide an excellent basis for future study of cuticular inflation function.
Highlights
The parasitic nematode Trichuris trichiura is a significant burden on public health in developing countries, and currently available drugs exhibit a poor cure rate
Cuticular inflations are outgrowths of the cuticle, which are separate from the bacillary cells that line much of the bacillary band as shown by Backscattered Electron Microscopy (BSEM) of a stained and resin-embedded sample (Fig. 1a)
Standard Scanning Electron Microscopy (SEM) was used to image female worms that had been extracted from the host gut at days 21, 23, 25, and 28 post-infection (PI) in order to track the morphological development of the cuticular inflations (Fig. 1b)
Summary
The parasitic nematode Trichuris trichiura is a significant burden on public health in developing countries, and currently available drugs exhibit a poor cure rate. Even the true exterior morphology of cuticular inflations is still uncertain, as in Scanning Electron Microscopy (SEM) images two forms are presented: either convex or concave This differential morphology is currently attributed to the drying process (freeze-drying or critical point drying) occurring during sample preparation causing naturally hydrated convex inflations to collapse into the concave form[16]. T. muris is the most suitable model for future hypothesis-driven investigation into cuticular inflations because larval development is well-characterised[3], allowing detailed study of worm development. A richer understanding of the epithelial niche and host-parasite interactions has been generated in the mouse model, allowing new ultrastructural information from Trichuris to be added to an extensive existing mosaic of immunological and cytological knowledge
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