Fluctuations in population size of Theileria orientalis Ikeda within the tick vector Haemaphysalis longicornis Neumann : an investigation into the life cycle of T. orientalis Ikeda : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Zoology, Massey University, Palmerston North, New Zealand
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2020
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Massey University
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Abstract
Theileria orientalis Ikeda is a protozoan parasite of cattle that causes disease through the destruction of the host's erythrocytes. In 2012, the parasite caused an epidemic of bovine theileriosis in New Zealand at great economic cost to the farming community. As a result, a large number of scientific studies have been undertaken to understand the epidemiology of the T. orientalis Ikeda parasite in the hopes of mitigating the damage done by the parasite. An essential part of the epidemiology of any pathogen is the understanding of its life cycle and this holds true with T. orientalis Ikeda which, like other Theileria parasites, exhibits a complex life cycle involving multiple hosts. In this thesis, fluctuations of T. orientalis Ikeda populations within nymph tick hosts were investigated over the course of six months. By doing so, this investigation highlights a part of the T. orientalis Ikeda lifecycle that is poorly covered in the scientific literature. The population of T. orientalis Ikeda within the tick was determined through qPCR analysis. Analysis of the qPCR results found that populations of T. orientalis Ikeda fluctuated greatly within the ticks over the course of six months. Ticks infected with Theileria were procured through the development of a novel mass tick- rearing protocol: the artificial infestation of a cattle-beast with naïve ticks through the fixation of tick-containing ear-bags. A pilot study of the protocol showed that the fixation of ear-bags onto cattle using Kamar® adhesive did not negatively impact the welfare of the cattle involved. The subsequent field trial of the protocol resulted in the successful engorgement and infection of five thousand naïve tick larva. These results demonstrated a viable method to obtain T. orientalis Ikeda infected ticks that would be suitable for further research. Also described in detail in this thesis are attempts at adapting the protocol of Krober and Guerin (2007) to create a silicone membrane for the artificial feeding of tick larvae on Theileria-infected blood without the involvement of live hosts. Despite multiple attempts, the experiments yielded no successful attachments of ticks onto the synthetic membranes. Failure here was attributed largely to the adapted protocol creating silicone membranes that were too thick for the larval ticks to successfully penetrate with their mouthparts. However, the in vitro feeding of ticks presents itself as a great potential contributor to future tick research. It is hoped that the knowledge gained from the repeated trials of the in vitro feeding apparatus in this experiment may help in the development of successful protocols in the future.
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