Visualising the parasitic whipworm Trichuris muris using X-ray micro-computed tomography
Trichuriasis is a tropical disease that affects an estimated 500 million people worldwide, especially children in tropical regions. It is caused by a parasitic nematode, Trichuris trichiura (whipworm). Current drugs lack efficacy, and there is no vaccine. Adult worms live partially buried in the mucosal epithelium of the intestine of the host, which makes them hard to study by traditional microscopy methods. As a consequence, little is known about how they feed, develop, and avoid the immune response of the host.
Micro X-ray CT of largely intact sections of intestine allows studying the intimate relationship between the parasite and host epithelium whilst avoiding the more damaging cutting of samples needed for 2D microscopy methods. In this contribution, we present data from adult Trichuris muris parasites found within infected mice. A scanning electron microscopy staining protocol was used for fixing and staining 5 mm sections of gut and caecum of the mice. Osmium tetroxide, used as a staining agent, was effective at producing x-ray absorption contrast in adult worms and their internal morphology, including the bacillary band, stichosome and oesophagus.
Novel observations about the positioning of the parasites were gained during this work. The heads of four out of six adult worms analysed were found to be orientated down the Crypts of Lieberkühn towards the basal lamina. Stichosome exposure to the lumen has relevance to novel drug development as epithelial penetrance of current anthelminthic drugs is poor. We measured the length of the exposed stichosome and the number of breaks in the epithelial layer covering the tunnel that the worm creates. Even though variance between worms is high, a part of the stichosome was always found to be exposed to the lumen.
We show that X-ray tomography is an effective approach to gain spatial and morphological information about Trichuris muris. In addition our data reveal T. muris in the mouse to be a useful model system with which to optimise imaging methodologies for the analyses of soft tissues in health and in disease.