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Title: The epidemiology and control of the louse Bovicola ocellatus (Piaget) in donkeys
Author: Ellse, Lauren Samantha
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2013
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Equine pediculosis is a significant welfare issue, particularly in elderly and chronically debilitated animals. In the UK, infestation is controlled predominantly using topically applied pyrethroid insecticides, allowing limited scope for the rotation of drugs and increasing the risk of selection for resistance. The work described in this thesis was undertaken in response to concern over a perceived high incidence of the donkey chewing louse, Bovicola ocellatus (Piaget)(Phthiraptera; Trichodectidae) at the Donkey Sanctuary in Devon and possible treatment failures. The aims were to determine whether the populations of lice present were resistant or tolerant to the insecticides most commonly used against them, whether there were alternatives that could be applied safely and whether risk factors could be identified that were associated with high louse burdens and that could be used to inform improved management strategies. The insecticidal ,efficacies of two of the pyrethroid-based products that were commonly used at the Donkey Sanctuary against B. ocellatus were examined in vitro (Chapter 2). The products were cypermethrin (Deosect™) and permethrin (Switch TM). The pyrethroid efficacy ,was contrasted with that of the organophosphate diazinon, since the louse populations examined had no prior exposure to this compound. The efficacy of pure permethrin, Switch™, the excipient butyl dioxitol and the effect of the synergist, piperonyl butoxide in combination with pyrethroids were also considered. At the concentrations recommended for animal treatment, neither 4% (w/v) permethrin, nor 0.1% (w/v) cypermethrin caused significantly higher mortality, of the B. ocellatus than an acetone-only control In contrast, 0.04% diazinon caused 70% mortality within 4 hand 100% mortality after 24 h exposure. The addition of a potential pyrethroid synergist, piperonyl butoxide, to cypermethrin and permethrin bioassays did not affect mortality rates. The data therefore, show that the population of lice from the Donkey Sanctuary's Devon display a high level of pyrethroid tolerance which is likely to reflect the development of resistance. Given the high level ofpyrethroid tolerance in this population of lice, there was an urgent need to identify alternative louse management approaches that fitted with the Donkey Sanctuary's commitment to high and sustainable standards of animal welfare. In vitro and in vivo trials were undertaken to assess the insecticidal efficacy of tea tree (Melaleuca alternifolia) and lavender (Lavandula angustifolia) oil against B. ocellatus (Chapter 3). Results of contact and vapour bioassays showed that 5% (v/v) tea tree and lavender oils resulted in >80% louse mortality after two hours of exposure. Mortality was significantly higher than in silicone oil controls and the vapour phase was insecticidal, indicating a neurological or cellular mode of action. On farms, separate groups often donkeys sprayed with 5% (v/v) tea tree and lavender oil as part of their usual grooming regime showed significant reductions in louse numbers compared to a control group (0.2% polysorbate 80 in water). These findings indicate that tea tree and lavender essential oils can provide clinically useful levels of control of B, ocellatus when used as part of a grooming routine and suggest that ,with further development could form the basis of an easy to apply component of a louse management programme for donkeys. A longitudinal study was undertaken over a 20 month period to examine the seasonal abundance and risk factors which predispose donkeys to pediculosis and to inform treatment protocols (Chapter 4). Overall pediculosis in these donkeys was over-dispersed, suggesting that some individuals are strongly predisposed to infestation. A strong seasonal pattern, which was correlated with mean monthly temperature, was observed with higher prevalence and intensity in the cooler, winter months (October/March). Donkey age and mean hair length were characteristics which affected louse prevalence: older and younger donkeys and donkeys with longer hair harboured the highest numbers of lice. However, clipped donkeys only had significantly lower louse prevalence than non-clipped donkeys in the summer, suggesting that clipping is not an effective form of louse control in cooler months. In addition, higher louse burdens were associated with larger areas of visible excoriation and hair damage, suggesting that B. ocellatlls does adversely impact animal welfare. However, the ability of grooms to estimate louse presence or absence accurately on an individual donkey was not sufficiently high to allow targeted selective treatment to be employed routinely. It is concluded that louse infestation in this large population of donkeys is a persistent and pernicious problem that will require a clear management plan to be designed and implemented rigorously if it is to be overcome. However, the results also have general implications for the management of louse populations in equids, particularly through the use of essential oils as a grooming aid.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available