Study on the pathogenicity of ostertagiosis due to Ostertagia circumcincta in sheep, in Iraq.

The response of Awassi sheep to ostertagia circumcincta, the most prevalent ovine strongylid species in Iraq, was studied. A dose of 100000 larvae of O. circumcincta (Iraqi strain) induced moderate clinical symptoms of ostertagiosis. These symptoms were correlated with elevated pH of the abomasal fluid and increased plasma pepsinogen levels. There was no evidence of larval inhibition since the majority of the fourth stage larvae (L4) continued their development. No appreciable loss of worm population was observed and most of the parasites survived and exhibited a prolific egg-laying potential six months after initial infection. Assessments of the pathophysiological changes were performed and correlated with parasitological and clinical observations. The Awassi breed of sheep, the most prevalent in the Arab Middle East, seems to be more susceptible to ostertagiosis than other breeds and there was no spontaneous self-cure in this breed.