Studies on the epidemiology and pathophysiology of ovine gastrointestinal helminthiasis

Yakoob, Alia Yousif (1982) Studies on the epidemiology and pathophysiology of ovine gastrointestinal helminthiasis. PhD thesis, University of Glasgow.

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This thesis is divided into two sections. In the first the literature pertaining to the epidemiology of ovine parasitic gastro-enteritis is reviewed and then, over a 2 year period, the epidemiology of this disease is studied in sheep from a flock which was housed each winter. In particular, the epidemiological effect of anthelmintic treatment of the adult sheep prior to turn-out in the spring and the interaction of the protozoal disease coccidiosis with the intestinal trichostrongyles N. battus are studied. The impact of anthelmintic treatment administered during the housing period on the subsequent epidemiology of trichostrongyles varied according to the drug used. where the drug levamisole was used the efficiency was sub-optimal, the ewes contaminated the pasture from the first day of grazing and the epidemiology of the disease did not vary from that in untreated flocks. In contrast, when the highly effective broad spectrum drug fenbdndazole was used the faeces of the ewes remained clear of nematode eggs for several weeks and the level of pasture infection was considerably reduced. By housing the sheep during the winter there v/as some indication in the first year that a build up of Eimeria spp oocysts occurred and both ewes and lambs shed many oocysts within 2 weeks of grazing. However, in the second year the number of oocysts shed were much reduced which suggested that the first year response. was due to favourable climatic conditions rather than the ingestion of massive numbers of oocysts indoors. Although severe nematodiriasis occurred due to N. battus infection in both years, the disease was more severe in the second year v/hen coccidiosis was apparently less prevalent and there was no indication that any positive interaction occurred between the two diseases. Two other interesting observations emerged from the study. The first was that larvated N. battus eggs hatched in the autumn of the year when the eggs were deposited and gave rise to increased pasture larval populations on the herbage and worm, burdens in the lambs. At the time these experiments were carried out this had not been recorded previously and eggs were thought to require a full winter exposure before hatching in the following spring. However, contemporaneous studies have recorded a similar phenomena and this may affect the current control measures based on a year to year hatching pattern. The second was, that the pasture larval sampling technique proved to be a much more sensitive indicator of pasture levels of infective larvae than did helminth-naive tracer lambs. This sensitivity of the pasture technique was particularly noticeable when pasture levels were high in 1980 but was also apparent throughout 1981. In the second part of the thesis the pathophysiological aspects of gastro-intestinal trichostrongylosis are reviewed and some of these effects are then studied in two experiment. In the first experiment radioisotopic techniques were used to assess the losses of plasma protein into the gastro-intestinal tract of naturally parasitised lambs. The leak of plasma protein was measured on three occasions using 51CrCl3 while total faecal 51 output was measured using chromic oxide. Losses of 51CrCl3 - labelled plasma protein were significantly higher in lmbs grazing heavily contaminated pasture than in those grazing lightly infected ground in two of the sampling occasions. The increased losses were associated with high trichostrongyle faecal egg counts hypoalbuminaemia and elevated plasma pepsinogen levels. This is the first time that a plasma protein leak has been positively demonstrated in grazing sheep. In the second experiment the effects of an experimental challenge with larvae principally of the abomasal nematode 0. circumcincta plus a few of the intestinal species, T. vitrinus Ch. ovina were measured in ewes, which had previously been exposed to infections with these parasites and were judged to be immune. Their immune status was shown by the presence of low worm burdens in both challenged and unchallenged ewes. However, despite those low worm burdens the larval challenge was associated with marked pathophysiological disturbances and in particular, elevated on plasma protein loss into the gastro-intestinal tract. The concurrent timing of these changes suggested that they- had a common etiology possibly associated with hypersensitivity reaction in the alimentary mucosa of immune sheep. The economic importance of this novel result is that impaired oduction of immune sheep may occur when they are under challenge and emphasises the need to control infections in ewes as well as in lambs.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: J Armour
Keywords: Animal diseases, Parasitology
Date of Award: 1982
Depositing User: Enlighten Team
Unique ID: glathesis:1982-71993
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 May 2019 13:29
Last Modified: 17 May 2019 13:29

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