Some aspects of immunity to the liver fluke Fasciola hepatica in sheep and cattle

Mitchell, George Bell Brand (1979) Some aspects of immunity to the liver fluke Fasciola hepatica in sheep and cattle. PhD thesis, University of Glasgow.

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The studies in this thesis were designed to investigate the comparative immunological responses of sheep and cattle to primary and secondary F. hepatica infection in order to more accurately define the reasons for the observed differences in susceptibility to the parasite in the two ruminant species. The effect of previous exposure to nematode and cestode infection in the course of F. hepatica infection in sheep was also studied. In Chapter I an extensive literature survey covering relevant aspects of the host-parasite relationship was carried out, and in Chapter II the materials and methods used in the thesis were described. In Chapter III the course of primary and secondary experimental F. hepatica infection in sheep was monitored and compared with that in experimental calves. This was done by performing various haematological, biochemical and parasitological procedures, including estimation of the liver enzymes G.L.D.H, and G.G.T. and detection of circulating antibody using D.I.D. and I.H.T. In this connection the microplate Enzyme-linked-immuno-sorbent assay (micro-E.l.i.s.a.) was investigated for early diagnosis of F. hepatica infection in ruminants. Problems associated with this technique were discussed in some detail. In addition the protective effect of serum from ruminants infected with the parasite was investigated in passive transfer studies in the laboratory model of fascioliasis. Following primary infection sheep rapidly became anaemic and remained susceptible to reinfection although serum from infected animals afforded a degree of protection when passively transferred to rats. In contrast, no anaemia was detected in experimental calves. The liver enzymes G. L.D.H. and G.G.T. were found to be reliable indicators of liver cell necrosis and bile duct damage, respectively, following primary infection in the two ruminant species, but proved of limited value on reinfection. D.I.D. and I.H.T. were found to be reliable diagnostic aids for detection of serum antibody, the former as a qualitative test and the latter as an early, sensitive quantitative indicator. E.l.i.s.a. was found to be both unreliable and idiosyncratic in tins system. Chapter IV described the response of peripheral lymphocytes of sheep and cattle to stimulation with various mitogens as well as F. hepatica somatic lipid-free antigen (L.F.E.) was monitored during experimental primary and secondary F, hepatica infection, using the Lymphocyte Transformation Test (L.T.T.). The patterns of responses obtained from infected and reinfected animals were compared with those of control animals. Differences observed in such patterns were noted and discussed in the context not only of the modifying effect of infection and reinfection on such responses, but also in terms of inherent differences in pattern of response between the two ruminant species. An immunosuppressive effect of F. hepatica infection was observed for the first time in experimental sheep, characterised by a reduction in the transformiug ability of peripheral lymphocytes in response, not only to nonspecific mitogenic, but also to specific antigenic (L.F.E,) stimulation. Such an effect was apparent not only in impaired responses of once-infected animals compared with control animals, but also when reinfected animals were compared with once-infected animals, thus suggesting that reinfection had reinforced the immunosuppressive effects. No such effects were demonstrable during experimental infection and reinfection of cattle in v/hich mitogenic and antigenic responses of infected and control animals was of a similar order. Possible reasons for the observed differences were discussed. The effect of prior nematode and cestode infection of sheep on the course of experimental F. hepatica was studied in Chapter V. The cross immunising properties of these parasites per se and in addition the modificationof any protective effect conferred by the immunomodulating compound L tetramisole (Levamisole) were investigated. In the final chapter of this thesis (Chapter VI) the various differences observed in the course of F. hepatica infection in the two ruminant species were described in some detail. The immunological shortcomings of sheep during F. hepatica infection were discussed with a vievv' to harnessing the therapeutic properties of such compounds as levamisole and "transfer factor" in a prophylactic regime incorporatuig the most recently developed specific immunogens in protecting not only sheep, but also cattle against fascioliasis.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: J Armour
Keywords: Animal diseases, Parasitology, Immunology
Date of Award: 1979
Depositing User: Enlighten Team
Unique ID: glathesis:1979-72402
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 24 May 2019 15:12
Last Modified: 24 May 2019 15:12

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