title: Studies on the pathophysiology and immune response to Ostertagia ostertagi in cattle
Creators: name: McKellar, Quintin Archibald
Publisher: name: University of Glasgow
Year: 1984
Subjects: subject: Animal diseases.

description: The studies reported in this thesis were undertaken to examine in detail several aspects of infection with Ostertagia ostertagi in cattle. The effect of age on the development of immunity was investigated and an attempt was made to immunise calves against O. ostertagi. More detailed work was concerned with the interaction of the parasite at the mucosal surface of the abomasum, together with the pathophysiological changes in the parasitised host. Section I describes two experiments on the immune response of cattle to Ostertagia. The first was designed to ascertain whether immunity to ostertagiasis developed more quickly in 9-15 month old cattle than in calves. Although there was evidence of two manifestations of resistance, namely reduced worm size and fecundity, the study demonstrated that worm establishment was not markedly affected by the age of the host and suggested that natural age resistance is not significantly developed in 9-15 month old cattle. In the second experiment, an attempt was made to immunise calves against O. ostertagi using a closely related parasite Ostertagia leptospicularis which has been shown to induce a marked reaction in the abomasum of calves. Two doses of either O. ostertagi. O. leptospicularis or a combination of O. ostertagi and O. leptospicularis were given to young calves prior to challenge with O. ostertagi but none of these immunising regimens conferred protection and similar challenge burdens were recovered from all of the calves at post mortem examination. The major part of this thesis was concerned with studies on the biochemical and hormonal changes which occur in the host as a result of infection with larval and adult O. ostertagi and these are described in Section 2. In Experiment 3, calves were infected with 50,000 O. ostertagi L3 and serum pepsinogen and gastrin levels measured; these rose markedly from day 15 after infection and peaked between days 20 and 30. Experiments 4, 5 and 6 were designed to investigate the role of the adult parasite in the pathophysiological changes in the host. Serum pepsinogen levels rose consistently when animals were exposed to adult parasites. However, serum gastrin levels only rose in response to large numbers of adult worms and the association of these changes with altered abomasal pH are discussed. Lesions were observed in the abomasa of calves which were infected with adult parasites only and a further experiment (Experiment 7) was carried out to determine whether the intimate association of the parasites with the mucosal surface was responsible for the pathological and physiological changes which took place. During this study, it was apparent that adult Ostertagia were quickly killed when restricted and suspended in chambers in the abomasum and it was then concluded that the parasites require the microenvironment close to the epithelium for their survival. No pathophysiological changes were observed probably due to the early mortality of the adult parasites in this experiment. The two remaining experiments in Section 2 were designed to investigate changes in pepsinogen and gastrin levels which occur in naturally acquired Ostertagia infections in the field. Animals in Experiment 8 were kept for two seasons under typical husbandry conditions and plasma pepsinogen and gastrin levels were recorded regularly. Values for pepsinogen and gastrin rose to two peaks as Type I and Type II ostertagiasis developed and subsequently fell as the animals recovered. The pepsinogen levels did not return to pre-infection values either during the pre-Type II period, or during the second grazing season when immunity had developed. The aetiology of the raised pepsinogen values observed during the second grazing season were further investigated in Experiment 9. Immune adult dairy cows which had been housed for the winter period were challenged with Ostertagia larvae and blood was collected routinely for the estimation of serum pepsinogen and gastrin. Pepsinogen levels rose to about 3.0 i.U. Tyrosine within 3 days of challenge while gastrin levels remained at pre-infection levels. It was concluded that Ostertagia larvae may induce a hypersensitive response in the abomasa of immune cattle with a consequent leakage of pepsinogen into the blood.