Prevalence, spatial distribution, and risk of ticks, tick-borne disease, and lice on livestock farms in Great Britain

Abstract

Ticks and lice are ectoparasites of veterinary importance to UK livestock. Infestation of livestock can result in economic losses for farmers, caused by reduced animal health and productivity, either by direct feeding effects or through the spread of vector-borne pathogens. A detailed understanding of the prevalence, distribution and associated risk factors for infestation and subsequent vector-borne disease is important to allow effective and targeted control measures to be designed and implemented. Despite this, there is limited national data about tick or louse infestation on livestock farms. The aims of this thesis were to assess the prevalence, distribution, and risk of infestation of ticks and lice and associated vector-borne disease on sheep and cattle farms across Great Britain.
A retrospective questionnaire survey was sent to a nationally representitative demographic of sheep and cattle farms to collect data on the presence/absence of livestock infestation (Chapter 2). Tick infestation risk is shown to be spatially aggregated, with areas of significantly elevated risk in north Wales, northwest England and western Scotland (Chapter 3). Overall, the prevalence of farms reporting ticks was 13% for sheep farms and 6% for cattle farms, but in ‘hotspot’ clusters prevalence ranged between 48-100%. The prevalence of farms reporting lice was 16% for sheep farms and cattle farms (Chapter 6). ‘Hotspot’ clusters of farms with louse infestation were only identified for sheep farms, in Wales, northwest England and southwest Scotland, with prevalence in these areas ranging from 31-40%.
In the future, it is expected that tick and tick-borne disease risk will change, as tick distribution is strongly influenced by climate. However, Europe-wide models lack sensitivity when predicting future tick distributions. A spatial model was built to predict the future risk of ticks on livestock farms under a range of climate-change scenarios (Chapter 4). Both tick hazard and livestock exposure were incorporated into the model, to capture a niche which may be missed by broader-scale models. Overall, the probability of ticks on livestock farms was predicted to increase under future climate scenarios, particulary at higher altitudes and latitudes, further increasing the risk of tick-borne disease on farms in these areas.
Two of the production-limiting pathogens ticks transmit to cattle in the UK are the protozoa Babesia divergens, the causal agent of redwater, and Anaplasma phagocytophilum, the causal agent of tick-borne fever. The prevalence and distribution of Babesia spp. and A. phagocytophilum in ticks on cattle farms in southwest England, an area of identified high risk, was investigated through tick collection from cattle grazing areas (Chapter 5). B. divergens and A. phagocytophilum were identified from 21% and 88% of farms, respectively. There were multiple positive samples for Babesia on individual farms, suggesting that Babesia distribution is clustered within the tick population, and may impact clinical redwater cases more than cattle immunity or tick density.
The data presented in this thesis contribute to an understanding of the epidemiology of ectoparasite infestation on British livestock farms. Findings are discussed in relation to livestock ectoparasite control and management strategies, and future changes in risk factors for infestation, such as land-management (Chapter 7).

Date of Award	9 May 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	Laura Peachey (Supervisor) & Richard Wall (Supervisor)