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Title: A study of Aelurostrongylus abstrusus, with special reference to pathogenicity
Author: Hamilton, John M.
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1968
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Abstract:
The purpose of the work recorded in this thesis was to investigate aspects of the several stages of the lungworm Aelurostrongylus abstrusus together with the effects of the parasite on intermediate, paratenio and final hosts. With regard to first-stage larvae, an estimation of the number produced by infected cats revealed that millions of those forms were excreted over a patent-period of between nine and ten weeks. Furthermore, such larvae had the ability to survive dehydration and extremes of temperature for varying periods of time. Aelurostronpylus abstrusua requires an intermediate host in which to complete its life-cycle and, in the past, there has been controversy as to the role of the mouse in that event. Experiments, herein described, indicated that, although the latter species was not a true intermediate host for the lungworm, it was able to act as a paratenic host and store third-stage larvae for at least four months. It was also confirmed that a snail, Helix aspersa, was a satisfactory intermediate host and that first-stage larvae invaded the sole of that mollusc, migrated into the deeper tissues during the course of the next twenty-four to forty-eight hours and, in twenty-three days, developed into third-stage infective larvae. The latter forms remained viable for the life-time of the snail. The majority of larvae was recovered from the muscular solo and, although a substantial number was extracted from other parts of the snail, it was considered that infection of the mollusc resulted from penetration of the pedal epithelium by, rather than ingestion of, lasrvae. The possibility of the existence of molluscan immunity was discussed. The effects of the parasite on the final host were ascertained. At least 100 third-stage larvae were necessary for successful parasitic infestation of the cat although, at that dosage, little clinical upset ensued. Numbers of 1,600 larvae, and more, produced increasingly severe clinical signs and pulmonary pathological changes while an infecting dose of 3,200 larvae was considered almost certain to be fatal. Because of difficulties inherent to the procedure of oral infection of cats, a parenteral method was tried but was found to produce inconstant results. Many metazoan parasites induce, In their hosts, an immunity which persists for a varying period of time and protects against further attack by the same parasite. Aelurostrongylas abstrusus was found not to be an exception and oats infested by the parasite 388 days earlier withstood re-infection. The outcome of an experiment, in which resistance to lungworm disease was passively transferred to oats by means of serum obtained from recovered animals, emphasised the importance of humoral antibodies in parasitic immunity. Following upon the results of the above experiments, the possibility of inducing active immunity in cats was considered. To that end, small numbers of unatteauated, infective larvae were administered to oats on three occasions and at monthly intervals and, at the end of the immunising regime, the animals were pathogenic with pathogenic doses of third-stage larvae. The results of that investigation showed that it was feasible to vaccinate cats against infection by Aelurostrongylus abstrusus. That section of the thesis was completed by an assessment of the effects of the lungworm on the pulmonary vasculature of the cat. Nine days after Infestation, hypertrophic change was noticeable in the medial coat of branches of the pulmonary artery and the arteriopathy was found to persist for a period of at least two years. Such evidence confirmed the previously-held Opinion of the author that spontaneous pulmonary arterial disease of the oat arose as a result of infestation, past or present, by Aelitrostrongylua abstrusus. The final part of the work was devoted to a study of diagnosis and treatment of feline parasitic pneumonia. The results of radiological examination showed that such a facility was of value in recognition of the disease. Of additional diagnostic worth was the Indirect Fluorescent Antibody technique by which procedure specific immunofluorescence was demonstrated to occur in sera taken from lungworm-infested oats. It was considered that the above examinations together with -careful clinical observation were able to provide sufficient proof of the presence of lungworm disease. With regard to therapy, diethylcarbamazine citrate was administered to a group of infected animals hut examination of faecal larval output as well as post-mortem study of the lungs of the oats showed that the drug had been unable to control or cure the condition. When six oral doses of the anthelmintic, tetramisole, were given to infected cats it was discovered that all stages of the parasite had been either eliminated or destroyed. However, the substance proved to be unpalatable to oats and evoked excessive salivation. To overcome that problem, resort was made to parenteral administration. It was then found that fairly small amounts of the chemical were toxic to, and caused death in, a number of experimental animals. Numerous doses were still required to abolish excretion of first- stage larvae from the faeces of treated animals and it was decided that parenterally-administered tetramisole had little advantage over that given orally. The thesis was concluded by a review of the work completed, and of the problems yet unsolved, with regard to the many facets of the lungworm, Aelurostrongylus abstrusus.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.776533  DOI: Not available
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