Some problems associated with the vaccination of ruminants against helminth infections

Benitez-Usher, Carlos Antonio (1975) Some problems associated with the vaccination of ruminants against helminth infections. PhD thesis, University of Glasgow.

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Abstract

The study in this thesis was concerned with investigations into 3 separate problems which have arisen in the development of immunisation procedures against 3 separate and serious helminth diseases of cattle and sheep. The comparative efficiency of two techniques used to monitor the number of nematode larvae on herbage was also examined. In Section 1, the previously unresolved problem concerning the immunisation of young milk-fed calves against the lungworm Dictyocaulus viviparus was investigated. Successful immunisation of weaned calves aged at least 8 weeks with two doses of X-ray attenuated infective larvae has been practised in Britain and Western Europe for some years now and the vaccine is commercially available as Dictol. The fact that immunisation with Dictol is not recommended until the weaned calves are 8 weeks-old has precluded the successful control of lungworm disease in dairy herds where calves are grazed from an early age and in beef herds where calves are suckled for several months. In the current studies, when Dictol was administered to pail-fed milk calves at 3 and 7 weeks of age the resistance to a subsequent experimental challenge 4 weeks later was excellent compared with non-immunised controls. As judged by the criteria of clinical signs, serological response and post-mortem lungworm burdens the immunity acquired by these young calves was comparable to that obtained in calves immunised at 8 and 12 weeks-old. When the immunisation procedure was repeated in suckled calves aged 3 and 7 weeks the degree of resistance to subsequent challenge was good but inferior to that obtained in pail-fed milk calves. Unfortunately, the situation was complicated by the presence of a Mycoplasma infection in the lungs of these calves, and it is possible that this and/or the blocking effect of maternal antibody may have influenced the result. Nevertheless, in the absence of any concurrent lung infection these experiments indicate that Dictol immunisation of young calves on a milk diet, whether suckled or pail-fed, appears to be a practical proposition and may result in more widespread and effective control of lungworm disease. In Section 2, immunisation with gamma-irradiated larvae of young calves against the abomasal nematode Ostertagia ostertagi was re-investigated. Previous studies had shown that the acquisition of a solid immunity to this parasite was slow and at best it was hoped that immunisation would limit the infection acquired to a tolerable level. In 1973, parasite-naive calves aged 8 weeks-old were immunised with 2 doses of 100,000 O. ostertagi larvae gamma-irradiated at 60 Kr and administered orally at an interval of 4 weeks. When subsequently grazed on pasture with a high level of O. ostertagi infection the calves failed to develop a significant resistance and clinical disease of an intensity similar to the controls developed in the immunised calves. In 1974, the immunisation procedure was repeated when the initial level of pasture infection was low. Although some immunised calves developed mild ostertagiasis, a moderating effect of the vaccine was apparent in that these calves acquired lower worm burdens than the controls, the clinical disease was milder and the subsequent level of infection on the pasture was lower than in the area grazed by the controls. It is doubtful however if this form of immunisation has any practical value for the control of ostertagiasis. An interesting feature of both experiments was the apparent suppression of Dictol-induced immunity in calves which had prior exposure to severe ostertagiasis. In Section 3, the pasture levels of O. ostertagi and D. viviparus larvae were monitored and compared using two techniques, one involving sieving and filtration of the herbage washings, and the other repeated sedimentation of the washings; recovery of both species was approximately similar when over 100 L3/Kg of herbage were present. Finally, in Section 4 some factors affecting vaccination of lambs against the stomach worm Haemonchus contortus with larvae attenuated by gamma-rays were studied. The results confirmed the inability of parasite-naive young lambs, aged 3 months to develop any immunity to challenge with H. contortus following the administration of 2 doses of attenuated larvae at an interval of 4 weeks.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Advisers: G M Urquhart; J Armour
Keywords: Animal diseases, Parasitology
Date of Award: 1975
Depositing User: Enlighten Team
Unique ID: glathesis:1975-72418
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 24 May 2019 15:12
Last Modified: 24 May 2019 15:12
URI: http://theses.gla.ac.uk/id/eprint/72418

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