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Title: Does Neospora caninum cause death by multiplying uncontrollably in an immunologically immature foetus?
Author: Gibney, Elizabeth Helen
ISNI:       0000 0004 2672 3872
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2008
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The last two decades have seen the emergence of the protozoan parasite Neospora caninum as the most frequently diagnosed cause of bovine abortion in the UK. The polymerase chain reaction (PCR) is a commonly used tool for molecular diagnosis. In chapter 2, the relative diagnostic sensitivity of two PCR protocols routinely used within our laboratory for the detection of N. caninum in tissues from aborted foetuses was determined. Method one was a nested PCR method based on the internal transcribed spacer I region of the rRNA sequence and was consistently more sensitive than method two, a single step PCR designed to amplifY a fragment of Nc5 N. caninum-specific genomic DNA, in our laboratory environment. Method one was therefore used to analyse samples for the rest ofthe experiment. It is not fully understood why some infected cattle abort, but previous studies have shown that abortion is more likely if transplacental spread ofthe parasite occurs early in gestation. Bovine foetal immunocompetence develops gradually during the second half of gestation, and it has been suggested that the immunocompetence of the foetus at the time of infection may determine its ability to control parasitaemia and survive. To test this hypothesis in chapter 3, we compared the distribution of parasites and the histopathological changes in the placenta and foetus following experimental infection of cattle with N. caninum in early and late gestation. In early gestation, following foetal death, N. caninum DNA was detected and evidence of widespread parasite infiltration was demonstrated immunohistologically in the placenta. This was associated with extensive focal epithelial necrosis, serum leakage and a moderate maternal predominantly CD4+ mononuclear cell interstitial inflammatory response. Widespread parasite infiltration was also evident in the foetus, with parasites in most tissues, often associated with necrosis. In late gestation, N. caninum DNA was detected sporadically but parasites were not evident immunohistologically in the placenta. Small foci of necrosis were seen occasionally, with a mild CD4+ and CD8+ mononuclear cell interstitial inflammation. Detection of N. caninum DNA in the foetus was sporadic and parasites were demonstrated immunohistologically in brain and spinal cord only, with an associated non-suppurative inflammatory response. We further investigated the pathogenesis of abortion in chapter 4, where we monitored ten chronically infected cattle throughout gestation and parasite recrudescence was pinpointed in 9/10 via a sharp rise in N. caninum-specific antibodies.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral