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Title: Studies of the immunology and epidemiology of orf
Author: McKeever, Declan James
ISNI:       0000 0001 3625 0894
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1987
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The responses of seven sheep to orf virus infection were examined by cannulating the efferent supramammary lymphatic before infecting the drainage area of the node. All animals developed lesions typical of orf virus infection, and responded after an initial lag period with an increase in total cell output paralleled by an increased proportion of lymphoblast cells. The majority of these lymphoblasts contained immunoglobulin, with a predominance of the IgG class. When efferent lymph cells from four of the sheep were cultured in vitro they were found to produce measurable amounts of virus specific antibody. When assessed in two of the sheep, the proportion of cells which stained with a T-cell-specific monoclonal antibody was found to decrease as the response developed. In contrast, analysis of afferent lymph (derived from efferent prefemoral lymphatics cannulated eight weeks after removal of the node) in four sheep revealed no marked cellular changes following experimental infection. The serological responses of naturally and experimentally infected lambs to orf virus infection was analysed using an enzyme-linked immunosorbent assay (ELISA) together with the Western Blotting technique. The combination of these methods permitted a quantitative and qualitative assessment of humoral responses, which revealed considerable variation between animals. However, all post-exposure sera reacted with a polypeptide which appears to be a component of the surface tubules which are characteristic of the virus. Despite high titres in some animals, there was no apparent association between humoral responses and recovery or protection. The heterogeneity of the orf virus population within the UK was examined using the restriction enzyme EcoRI by digesting viral DNA prepared from scab material derived from various outbreaks, and separating the fragments by electrophoresis in polyacrylamide gels. This technique revealed obvious genomic differences among the isolates which were examined, extending even to those derived from animals undergoing synchronous infections on the same premises. By subjecting orf scab material to various contrived environmental conditions both indoors and outdoors, it was shown that exposure to rainfall can abrogate infectivity of the virus, which questions the significance of virus persisting on pasture as a source of infection. Two rams which were shown to suffer from chronic orf infection suggest that the virus is capable of surviving inter-epizootic periods within the animal population. These animals had high serum antibody titres, but exhibited reduced delayed hypersensitivity responses to intradermal challenge with orf virus when compared with control animals. It was concluded that humoral responses play little or no part in recovery and protection from of virus infection, and that immunity is manifested by an accelerated reaction which is the result of a delayed hypersensitivity response.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Ovine orf virus infection