A study of feline calicivirus plaque types

Ormerod, Edward (1979) A study of feline calicivirus plaque types. PhD thesis, University of Glasgow.

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Genetic variation among Feline caliciviruses (FCV) was studied using the plaque character of an isolate as a marker. The basis for differences between isolates in plaque size and the relationship between plaque type and virulence was examined. Initial work, reported in Chapter 3, required to formulate a plaque assay method which was efficient and statistically acceptable as a particle counting system. To facilitate the differentiation of different plaque size populations it was found necessary to treat cultures with anti-virus serum or wash them with medium after virus adsorption. It was observed that there was wide variation in plaque size between FCV strains (chapter 4). Strains were arranged into four groups based on plaque size which were designated minute plaque (mp), small plaque (sp), large plaque (ip) and extra-large plaque (ep). The development of plaques of a number of strains, and significantly all mp forming strains, was found to be inhibited by the sulphated polysaccharide-containing fraction of agar. Evidence was presented which indicates that the plaque morphology of FCV is a highly mutable characteristic and that selection of smaller plaque variants (mp and sp) frequently occurs when isolates are passaged in cell culture. A correlation between plaque size and virulence was noted (chapter isolates belonging to the mp group were all of low virulence whereas two highly virulent isolates belonged to the ep group. This correlation was investigated in detail by comparing the disease produced by two cloned Isolates, Gl (ep forming) and GIO (mp forming) in specific pathogen free cats and by comparing their in vitro biological characteristics (Chapter 6). In vivo, Gl produced a more widespread Infection than GlO with higher titres of virus present in turbinate and lung tissues sampled at necropsy in vitro, the main reason for the large difference in plaque size between these isolates was demonstrated to be polyanion inhibition of the mp forming isolate although differences were also detected in growth curves which probably contributed to the plaque size difference. It was postulated that these different biological characteristics might also explain the observed difference in virulence between mp forming and ep forming isolates. An electron microscopic study of isolates G1 and G10 and a number of FCV strains revealed inter-strain variation in the cytopathology induced hy virus in cell culture, particularly in the way virions accumulated in infected cell cytoplasm prior to release. For example, G1 virus accumulated in large paracrystalline arrays whereas G10 vims remained in loose aggregates and occasionally in linear arrays. Interstrain differences in antigen distribution were detected by immunofluorescent microscopy and it was suggested that these might be, at least in part, produced by different types of virion accumulation. There was no apparent correlation between the cytopathology induced by a vims strain and its plaque type or virulence. These observations did, however, suggest an ultrastructural basis for differences observed in single step growth curves.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: O Jarrett
Keywords: Veterinary science
Date of Award: 1979
Depositing User: Enlighten Team
Unique ID: glathesis:1979-72707
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06
URI: https://theses.gla.ac.uk/id/eprint/72707

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