Inhibition of Gastric Hydrochloric Acid Secretions in the Rat Given Ostertagia ostertagi (a Gastric Parasite of Cattle) Extract

The immersion of freshly collected Ostertagia ostertagi adults into saline solution (NaCl, 0.9%; pH 1.0) resulted in 100% mortality of worms within a 10-minute period. At pH 7.0, mortality was 58% after 270 minutes. At pH 2.2, which approximates the usual abomasal pH, 100% mortality resulted within 60 minutes. In the stomach of rats injected with an extract of O ostertagi (from the abomasum of cattle), there were decreased total secretion of hydrogen ions and volume of secretion (P less than 0.05) and increased mean pH of gastric secretion (P less than 0.05). These effects were similar to those found in stomach of rats treated with cimetidine. Results indicated that the pH of the abomasum was detrimental to parasitic survival and that hypochlorhydria found during ostertagiosis may be mediated partially by a chemical released from the parasite.