The location of parasites within their hosts: Site selection by Trichuris muris in the laboratory mouse

Panesar T. S. and Croll N. A. 1930. The location of parasites within their hosts: site selection by Trichuris muris in the laboratory mouse. International Journal for Parasitology10: 261–273. This paper examines those factors which determine the location of T. muris in the caecum and colon of DBA-2 male mice. In caecectomized mice, infected post-operatively, T. muris established in the ileum. Despite the very different surface architecture of the ileum T. muris thrived within the epithelium lining the villi, comparable to their cytological microhabitat in the caecum. Unembryonated eggs of T. muris collected passively in the caecum, and embryonated eggs hatched readily in vitro when placed in caecal contents. These factors, together with the transit time of eggs which reached the caecum in 1 to 6 h, probably account for this being the major location for this nematode. T. muris could be successfully transplanted from caecum to caecum at 5 and 10 days post-emergence but not afterwards. This has been interpreted to result from the inability of the older worms to re-establish the intimate intra-epithelial association and to re-excavate their characteristic tunnels. T. muris caused a significant increase in the pH of luminal environment of the caecum and the colon of infected mice. The influence of post-operative changes in the gastrointestinal tract of mice causing compensatory anatomical changes is reviewed but considered to be insignificant in the present study.