The histotropic phase of the nematode parasite, Ostertagia circumcinta.

Abstract

The histotropic phase of Ostertagia circumcincta in the abomasal mucosa of the sheep has been investigated. Larvae were found to enter the gastric pits and glands and there pass the third ecdysis, three days after oral administration to the host. Some of these larvae failed to grow after ecdysis, and were found in the mucosa as long as three months from the date of infestation. Other larvae migrated into the lumen of the abomasum immediately after ecdysis. Still others developed in the mucosa, and migrated to the lumen of the abomasum either when adult or else during the fourth stage. The greater number of larvae were found in the mucosa in the pyloric region and around the cardiac orifice. A small proportion were found in the fundic region, where they formed large, flattened nodules. Histological examination showed that the peptic, parietal, and mucous chief cells had been replaced in these nodules by foveolar cells. This cycle of degeneration and subsequent regeneration of the specialized gastric cells appeared to follow a pattern which has been recognized in the dog and some other animals. Larvae in the histotropic phase are unlikely to be affected by drenches. The significance of these larvae in the epidemiology of ostertagiosis is unknown. It is suggested that larvae which develop in the mucosa utilize cellular secretions for nourishment.