Light and electron microscopical studies of the location of Strongyloides ratti in the mouse intestine.

This study was designed to define the precise anatomical location of Strongyloides ratti in the intestinal mucosa of the mouse. Light microscopy showed adult worms in vacuoles in close relationship with the columnar epithelium. Serial sections indicated that the adults wound their way circuitously through the mucosa, usually close to the crypts. Portions of worms were sometimes seen in the intestinal lumen. Electron microscopy demonstrated that adult worms were situated between the epithelial cells. They were never observed to penetrate the basement lamina and enter the lamina propria. Enterocytes were in close proximity to the cephalic end of worms, suggesting that the head of the moving worm forced the cells apart. More posteriorly along the worm, a fluid-filled vacuole surrounded the nematode. The surrounding epithelial cells were compressed and distorted but there was never any evidence of syncytial cell formation. The external cortical layer of worms was seen in some vacuoles, suggesting that ecdysis may occur in tunnels in the epithelium. It appears that S. ratti may create epithelial tunnels through which it moves, moults and deposits eggs. Since S. ratti is a mucosal-dwelling parasite, it is susceptible to attack by cellular elements of the host's defences.