Studies on pharmacological mediation of helminth infection in sheep

Mitchell, Elizabeth Sian (1987) Studies on pharmacological mediation of helminth infection in sheep. PhD thesis, University of Glasgow.

Abstract

The first section of this thesis deals with general methods of experimentation and materials used in this period of study The second section describes experiments to study the effects of a non-steroidal anti-inflammatory drug on the responses of sheep of various degrees of immunity to a challenge of Ostertagia circumcincta Treatment with meclofenamic acid of adult immune sheep tended to reduce the number of parasites at necropsy, but did not alter the plasma pepsinogen response after challenge when compared to untreated controls, A similar result was obtained in the study with previously parasite-naive lambs Meclofenamic acid treated animals contained fewer parasites at necropsy, but plasma pepsinogen activities were similar to untreated controls Finally, previously parasite-naive lambs were infected with adult circumcincta parasites All animals showed parasite eggs in the faeces indicating establishment Those animals which received parasites from untreated donors, and were themselves untreated with meclofenamic acid showed a rise in plasma pepsinogen activities, which was not observed in the other, groups Meclofenamic acid was subsequently found to inhibit parasite larval motility in vitro which could explain the above results Section three is concerned with the effects of various drugs on the responses of adult immune sheep to Ostertagia circumcincta challenge Treatment with a corticosteroid allowed larger numbers of parasites to establish and produced higher plasma pepsinogen activities Leukotriene C4 concentration in gastrointestinal mucus was lower than that measured in the other groups, producing evidence for a possible protective role of this substance against parasites Sheep treated with a mucolytic, bromhexine hydrochloride had fewer parasites at necropsy and lower plasma pepsinogen activities when compared to the control group Omeprazole, a drug that raises intra-abomasal pH produced unexpected results Plasma pepsinogen activities rose towards the end of the experiment However parasite numbers were very small at necropsy Omeprazole treatment may have altered plasma pepsinogen activity, either directly by its action on abomasal pH or via stimulation of gastrointestinal hormones e g gastrin Alternatively, its effect may have been to allow the larval challenge to establish, but when the adult parasites emerged, the omeprazole treatment having finished, the host was able to remove them The responses of isolated gastrointestinal smooth muscle were studied in section four Contractions of the tissue in response to acetylcholine was the consistent feature of both bovine and ovine abomasal and duodenal smooth muscle Histamine and prostaglandins E1 and E2 generally caused contraction of bovine duodenal preparations In contrast, few ovine duodenal preparations contracted to prostaglandins E1 and E2 and histamine 5-hydroxytryptamine and leukotrienes B4, C4 and D4 failed to produce a response in the smooth muscle of abomasal and duodenal preparations tested Administration of O. circumcincta homoqenates to ovine abomasal and duodenal tissues from immune animals failed to produce a Schultz-Dale reaction In vitro studies using parasitic larvae were presented in section five Faecal and mucus homogenates from immune animals did suppress larval motility in the test system used Prostaglandins E1 and E2 and leukotriene C4 also appeared to have an adverse effect on parasite motility The usefulness of these studies to investigate the effectiveness of possible anthelmintic drugs was also discussed The final section deals with studies carried out on benzimidazole-resistant strains of O. circumcincta One strain (HERO resistant) was passaged through lambs and the effect of treatment with fenbendazole monitored using the egg hatch assay as a measure of the level of resistance of the strain Daily variations in the level of resistance were detected Despite passaging of this strain through five lambs and treatment with fenbendazole on four occasions, the level of resistance did not alter Another resistant strain (Moredun) was investigated and found to have a lower level of resistance than the HFRO strain.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Animal sciences, Animal diseases, Parasitology, Veterinary science
• Date of Award: 1987
• Depositing User: Enlighten Team
• Unique ID: glathesis:1987-76685
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 13:54
• Last Modified: 19 Nov 2019 13:54
• URI: https://theses.gla.ac.uk/id/eprint/76685