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dc.contributor.authorRios de Alvarez, Leyla.en
dc.date.accessioned2018-05-22T12:47:27Z
dc.date.available2018-05-22T12:47:27Z
dc.date.issued2010en
dc.identifier.urihttp://hdl.handle.net/1842/30686
dc.description.abstracten
dc.description.abstractThe central aim of this study is to investigate the mechanisms of action of plant secondary metabolites (PSM), their direct effect on gastrointestinal nematodes (GIN) and their indirect effect on the local immune response of parasitised sheep. The first approach was through an in vivo study using a tannin-rich crop, sainfoin (Onobrichys viciifolia), for feeding growing lambs trickle infected with Trichostrongylus colubriformis. Thirty-two lambs, 16 weeks of age, were allocated to 1 of 4 treatment groups (n=8) that were offered either grass (G) or sainfoin (S) hay from day -14, while concurrently either infected (+), or not (-) with 12 000 L3 T. colubriformis larvae per week, from day 0, for 6 weeks. Liveweight gains were affected by diet (P=0.002) and reduced by infection (P<0.005). Faecal egg count was reduced in the S+ group compared with the G+ group from days 35 to 42 (P=0.001); however, total egg output, worm burdens at day 42 and worm fecundity were similar between diets (P>0.05). Feeding sainfoin appeared to enhance immune cell development with tissue eosinophils, mast cells and Pan T cells present in greater concentrations in S+ than in G+ animals. However, further studies are required to determine if the enhanced immune cell development is a consequence of a greater nutrient supply or a direct influence of sainfoin metabolites on local inflammatory responses to the gastrointestinal nematode T. colubriformis.en
dc.description.abstractThe second approach was to investigate in vitro the potential anthelmintic effect of PSM different from tannins, namely plant lectins. Phytohaemagglutinin E3L (PHA-E3L), Wheat germ agglutinin (WGA) and Concanavalin A (Con A or Jack bean lectin) were used with the larval feeding inhibition assay (LFIA), where the direct effect of the lectins at different concentration on the feeding of first stage larvae (LI) was investigated. The results showed that these plant lectins had a profound effect on the feeding of the larvae, especially PHA E3L (P=0.0006) at low concentrations, while Con A and WGA were effective at higher concentrations and T. colubriformis appeared to be the most susceptible (P=0.07) of the three nematode species tested.en
dc.description.abstractIn a third approach the intriguing results achieved with the LFIA employing plant lectins were confirmed through an in vivo experiment. Twenty-four lambs were allocated to one of four groups (n=6) in a 2x2 factorial design with treatments being either infection (-P: no infection vs. +P: mixed infection with Teladorsagia circumcincta and T. colubriformis) or PHA administration (-L: no PHA vs. +L: oral dose of 80 mg PHA/animal/d), for 6 weeks. Animals received a dose of 167 mg/animal/d of 40.24% w/w semi-purified PHA lectin (equivalent to 80 mg of pure PHA) administered orally five times per week. Compared with their non-dosed counterparts, PHA significantly reduced the faecal egg counts (epg) between days 25 and 36 post infection (P=0.033) and had a tendency to reduce the ability of larvae to penetrate abomasal tissue (P=0.063), as evaluated by an in vitro direct challenge assay (IVDC) used to investigate the effect of lectin treatment on the ability of the larvae to penetrate the mucus layer and migrate to the gastric pits in the abomasal tissue. PHA did not affect cell populations of the intestine. In abomasal tissue of parasitised animals, PHA induced an increase in the number of eosinophils (P<0.001) and PAS-positive cells (P=0.034). No changes in mucosal mast cells were observed in any of the animals. These results indicate that the oral dosing of PHA may affect local mucosal immune responses during GIN infection, although further studies are required to define both the direct and indirect effects of PHA in vivo.en
dc.description.abstractA clear direct effect of lectins in vitro on the feeding of first stage larvae was found in the laboratory and clear evidence of an enhanced immune response of the host was shown through both in vivo studies. However, there is still more studies to be done to find the mechanisms of action of PSM on the GIN of sheep. The use of PSM or nutraceutical plants, seen from the perspective of being able to influence the immune response of the animals, 'immunoceuticals' is an important target for future studies. If we are able in the future not only to have a direct effect on the worms but also to induce changes in the immune response of the animals through their food, alternative parasite control methods could have an important role to play in commercial farm conditions.en
dc.publisherThe University of Edinburghen
dc.relation.isreferencedbyAlready catalogueden
dc.subjectAnnexe Thesis Digitisation Project 2018 Block 19en
dc.titleMechanisms of action of plant secondary metabolites and their effect on the immune response of parasitised sheepen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhD Doctor of Philosophyen


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