Australian plants and their bioactive compounds can offer a new option for controlling horse worms

    Research output: ThesisDoctoral Thesis

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    Cyathostomins are common intestinal parasites of horses worldwide. Control of these
    parasites relies largely on the use of synthetic anthelmintic pastes or drenches, however,
    anthelmintic resistance is increasing in prevalence. Hence, there is a need to investigate
    new methods of control. The overall objective of this research was to identify
    Australian plants with potential to control cyathostomin parasites. The main hypothesis
    tested in this thesis was that there are Australian plants with anthelmintic activity
    against cyathostomins, and the activity is due to plant secondary compounds. This
    hypothesis was addressed in three experiments.

    In the first experiment (Chapter 4), a number of Australian plants were screened in vitro
    to identify species with anthelmintic activity against cyathostomin larvae. Twenty-nine
    out of the 37 crude plant extracts tested had significant inhibitory effects on larval
    development. Seven plants, including Alectryon oleifolius and Acacia melanoxylon,
    completely inhibited larval development and had IC50 values ranging from 30.9 - 196
    μg of extractable solids/mL. This first experiment therefore confirmed that anthelmintic
    activity exists amongst Australian plants and that there was potential for them to be
    used as novel control methods for cyathostomins in horses.

    In the second experiment (Chapter 5), the plant A. oleifolius was investigated further.
    Procyanidin A2, a condensed tannin, was isolated from the plant through a process of
    bioassay guided fractionation and demonstrated a significant anthelmintic activity in
    larval development assays, completely inhibiting development at concentrations as low
    as 50 μg/mL and having an IC50 value of 12.57 μg/mL. Procyanidin A2 also
    significantly inhibited larval migration at concentrations of 25 μg/mL.
    The anthelmintic activity demonstrated by procyanidin A2 in the in vitro assays suggests that it could
    play a useful role in controlling cyathostomins in the future.

    In the third experiment (Chapter 6), the compound(s) responsible for the anthelmintic
    properties of A. melanoxylon was investigated further. A specific structure of an active
    compound was unable to be obtained via bioassay-guided fractionation, however,
    spectroscopic evidence suggested the compounds were similar to hydroxycinnamic acid
    esters known to be present in A. melanoxylon. Analogous compounds were synthesised
    or purchased from a commercial source and tested in vitro. Four hydroxycinnamic ethyl
    esters had significant anthelmintic activity in the larval development assays. Ethyl
    caffeate and ethyl ferulate completely inhibited development at 200 μg/mL, while ethyl
    p-coumarate and ethyl isoferulate completely inhibited development at 100 μg/ml.
    Additionally, ethyl p-coumarate significantly inhibited larval migration at 800 μg/mL,
    and other compounds also showed some activity at higher doses.

    The work presented in this thesis demonstrates that Australian plants have anthelmintic
    activity against cyathostomin parasites of horses. This is also the first time that
    compounds such as procyanidin A2 and hydroxycinnamic ethyl esters have been
    demonstrated to have anthelmintic properties. Further investigation, particularly in
    vivo, is needed in order to develop appropriate applications. However, the results
    indicate that either through using whole plant preparations or purified compounds,
    Australian plants could be a useful part of cyathostomin control programs in the future.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    • The University of Western Australia
    Award date13 Jul 2016
    Publication statusUnpublished - 2015


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