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Title: A comparison of the immune response and pathogenesis of sheep and cattle to Toxoplasma gondii infection
Author: Esteban-Redondo, I.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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Abstract:
Toxoplasma gondii is an extremely successful parasite capable of infecting all warm blooded animals. However, there is a wide variation between different animal species in their vulnerability to infection, providing a fascinating opportunity for comparative studies on the host/parasite relationship. The main purpose of this thesis was to compare primary oral Toxoplasma gondii infection in two animal species, sheep and cattle, which are thought to differ in their respective vulnerability to infection. The parameters examined were the immune responses, pathogenesis and persistence of the parasite within tissues. The rationale behind this study was based on reports that cattle seem to be more resistant to the outcome of Toxoplasma infection. Congenital disease is rarely reported and cattle are thought to harbour fewer parasite tissue cysts which may not persist for the life time of the host, whereas in sheep, a primary infection usually results in the host remaining chronically infected for life and may result in abortion if primary infection occurs during pregnancy. It was hoped that these studies may indicate the critical factors involved in controlling T. gondii infection and increase our understanding of the events leading to persistence of the parasite within tissue cysts in the muscles and central nervous system of infected food animals. T. gondii tissue cysts in animal meat are an important source of infection for people, and recrudescence of parasites within tissue cysts in the central nervous system of immunosuppressed people, is one of the most common causes of death of AIDS patients. Host immune responses, in particular T cells and IFNγ, are known to play an important role in determining the outcome of Toxoplasma infection. Much of the data on host immune responses is derived from the study of laboratory mice which are extremely vulnerable to infection. There is comparatively little data from other animal species. It is difficult to draw any precise conclusion as to why cattle may be less vulnerable to T. gondii infection than sheep. In general the cattle appear to be better able to control the parasitaemia resulting in fewer T. gondii cysts being detected in their tissues compared with sheep. Interestingly the cytokine IFNγ was more frequently detected either from plasma or activated cell supernatants in the infected cattle compared to the sheep. This cytokine is known to play an important role in protection against T. gondii and has been implicated as a factor involved in the differentiation of tachyzoites to bradyzoites (tissue cyst stage). Recent data would suggest that production of IFNγ can occur via NK cells very early in infection and that this may have a profound effect on the ability of the host to withstand infection. Future studies should perhaps focus on local responses at the very early stages of infection as measurement of peripheral immune responses may not be sufficiently sensitive.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.650045  DOI: Not available
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