Experimental Parascaris equorum infection in the foal

Clayton, Hilary Mary (1978) Experimental Parascaris equorum infection in the foal. PhD thesis, University of Glasgow.

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This thesis describes the results of a series of experimental studies of the life-cycle and pathogenic effects of one of the most common helminths of the foal, Parascaris equorum. The investigations showed that the larvae of equorum migrate through the liver and the lungs before returning to the predilection site in the cranial part of the small intestine, 2 to 4 weeks after infection. In foals under one month of age a high percentage of the infective dose completed this migration, regardless of the magnitude of the infection and subsequently the worms grew rapidly in the intestinal lumen. Following a small infection (160 eggs) most of the parasites developed to maturity during the ensuing 2 months, whereas after a large infection (8,000 eggs) there was an expulsion of worms in the faeces from the seventh week onwards, resulting in a progressive decrease in the number of worms present in the small intestine. The studies on the pathogenesis of P. equorum infection in young foals showed that the pulmonary migration was accompanied by mild respiratory signs of coughing and a nasal discharge. During the later stages of infection the development of substantial numbers of ascarids in the intestinal lumen was associated with unthriftiness and poor weight gains. Histological examination of the liver revealed the presence of an infiltration of eosinophils and lymphocytes and a fibrotic reaction around the portal triads, but there was no indication of any impairment of hepatic function in these experiments. In the lungs a cellular infiltration, consisting primarily of eosinophils which were later replaced by lymphocytes, was particularly marked around the small blood vessels arid airways. An increasing number of raised, spherical, lymphocytic nodules developed during the fourth to sixth weeks, a few of which were still evident several months later. The only significant haematological change was the development of a circulating eosinophilia 3 to 5 weeks after infection, which corresponded to the periods of hepatic and pulmonary eosinophilia. Alterations in the serum protein levels were not recorded. After studying the effects of P. equorum infection in young foals, further experiments were designed to investigate the development of immunity to this parasite. Experimental infections of worm-free and naturally reared foals, aged 6 to 12 months, showed that, compared with the younger animals, only a small number of larvae returned to the gastrointestinal tract but the hepatic and pulmonary lesions were increased in number and severity. The findings were identical in the worm-free and naturally roared groups and suggested the development of an age-dependent immune reaction operating at the level of the parenchymatous organs. Although the respiratory syndrome was more severe in the older animals, unthriftiness was not a feature due to the reduced number of worms present in the small intestine. The prepatent periods ranged from 80 to 104 days, but the length of the prepatent period could not be correlated with either the age of the foal or the magnitude of the infection. In foals over 6 months of age patent infections occurred less frequently and the faecal egg counts tended to remain low.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: G M Urquhart
Keywords: Animal diseases, Parasitology
Date of Award: 1978
Depositing User: Enlighten Team
Unique ID: glathesis:1978-73180
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56
URI: http://theses.gla.ac.uk/id/eprint/73180

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