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Title: Haemonchus contortus and hookworms : parallels in vaccine development
Author: Clark, Douglas Alexander Stuart
ISNI:       0000 0001 3553 6786
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2006
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The recognition of hookworm infection as a leading cause of global morbidity has led to the establishment of a major initiative to develop a vaccine against human hookworms. Lead candidate hookworm antigens have been selected on the basis of either their association with the dog hookworm attenuated larval vaccine or because they are homologues of the major vaccine candidates from the related species of veterinary importance, Haemonchus contortus. Some of these hookworm antigens have been established as modestly protective in recombinant form, but have not been tested as native proteins. Higher levels of protection against homologous challenge have been achieved using the corresponding native H. contortus antigen in sheep trials. The feasibility of obtaining native protein from H. contortus and the convergence of vaccine targets in hookworms and H. contortus render the latter a useful model to aid vaccine development against the former. Homologues of the major larval hookworm vaccine candidate antigens thought to play a role in the transition to parasitism (Ancylostoma secreted proteins, an astacin- like metalloprotease and a transthyretin-like protein) have been sought in H. contortus with a view to assessing their efficacy as protective antigens against this infection in sheep. H. contortus larval excretory/secretory proteins were collected and fractionated by affinity chromatography into lentil lectin-binding and non binding fractions. The former was purportedly enriched for an Ancylostoma secreted protein 1 homologue and the latter shown to contain metalloprotease activity. A sheep protection trial demonstrated the lectin-bound fraction had a modest protective effect indicated by a trend towards lower faecal egg count, a significant 16% reduction in worm burden and a reduction in the length of female worms. Vaccination with the non-binding fraction showed a trend towards reduced faecal egg count and worm burden and sera from vaccinated sheep inhibited larval establishment in an in vitro abomasal challenge model The full length sequence of the H. contortus larval ASP-1 homologue was established, and the transcript shown to be expressed by exsheathed larvae and adult worms. However, expression of the recombinant protein was not possible thus definitive establishment of the protein within the lectin-binding ES fraction not confirmed. Novel homologues of the hookworm transthyretin-like protein and astacin-like metalloprotease were identified in H. contortus, cloned and characterised. The former was expressed in all life stages and immunolocalised to the lining of the uterus wall and on the surface of the eggs in utero as well as in the sub-cuticular muscle. Degenerate PCR followed by rapid amplification of the cDNA ends identified full length sequence of the latter, a novel astacin-like metalloprotease, the protein product of which was immunolocalised to foci within the exsheathed larvae immediately sub-cuticular to the lateral alae, possibly labelling the hypodermal chords. This work has established the modest protective effects of fractionated larval ES thus indicating the proteins therein to be of protective potential. Homologues of the lead hookworm larval vaccine candidates in H. contortus have been identified and these may have potential as larval vaccine candidates against homologous challenge.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available