Veterinary Clinical Sciences - Theses
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ItemExploring oriental theileriosis in bovines using advanced molecular tools( 2018)Theileriosis is caused by tick-borne haemoprotozoan parasites of the genus Theileria spp. and is one of the most economically important diseases of bovines, particularly in tropical and sub-tropical regions of the world. Of the different forms of bovine theileriosis, oriental theileriosis, caused by one or more genotypes of T. orientalis, has become an important emerging tick-borne disease linked to substantial economic losses in cattle, particularly in the Asia-Pacific region. Based on the sequence analysis of the major piroplasm surface protein (MPSP) gene, at least 11 distinct genotypes of T. orientalis (types 1-8, and N1-N3) have been recognised globally. Of these, 11 currently known genotypes, types 1 (chitose) and 2 (ikeda) are usually associated with clinical oriental theileriosis in cattle in the Asia-Pacific region. The present thesis was chiefly aimed at exploring epidemiological aspects of oriental theileriosis in bovines from different countries and improving the diagnostic methods used for this disease. This thesis comprises of a literature review, seven result chapters and a general discussion. In Chapters 2 to 4, the applicability of a standard PCR and multiplexed tandem PCR (MT-PCR) followed by mutation scanning and phylogenetic analysis as well as different conventional diagnostic methods were used to assess the spread of T. orientalis infections associated with cattle movement within Australia and from Australia to Vietnam and to Pakistan. The results of these Chapters revealed the presence of genotypes buffeli, chitose, ikeda and type 5 of T. orientalis at high prevalence and intensity of infection, and genotypes chitose and ikeda were shown, for the first time, to be associated with oriental theileriosis outbreaks in South Australia (beef cattle) and Vietnam (imported dairy cattle). In addition, the MT-PCR assay was sensitive and specific for the rapid and reliable detection of four genotypes (buffeli, chitose, ikeda and type 5) of T. orientalis in cattle involved in oriental theileriosis in Australia and other countries. Cattle movement was shown to be a major risk factor for the spread of oriental theileriosis from endemic to non-endemic regions, and the recommendation was made that cattle should be tested before and after movement, in order to control the spread of the disease using advanced molecular tools such as MT-PCR. In Chapters 4 and 5, the established MT-PCR followed by MPSP-PCR phylogenetic analyses were applied in areas where the prevalence and genetic diversity of T. orientalis complex were previously unknown (e.g., in Ethiopia and Pakistan). Using these methods, four genotypes (buffeli, chitose, ikeda and type 5) of T. orientalis were detected in both countries with low prevalence and intensity of infection in bovines. The results indicated the broad applicability of the MT-PCR to T. orientalis infections in countries other than Australia and New Zealand. The impact of oriental theileriosis in bovines and local vectors are unclear in these countries, and further large-scale molecular epidemiological studies in different ecological and climatic zones are required. In Chapter 6, the cost-effectiveness of pooled cattle blood samples compared to the testing of large individual cattle blood samples by MT-PCR was assessed for the diagnosis of the two pathogenic genotypes chitose and ikeda of T. orientalis. The results revealed that the testing of pooled blood samples (pools of 5 or 10) was costeffective to screen herd-level prevalence and animal-level prevalence (in regions with low disease prevalence) for T. orientalis, and can significantly reduce the time and cost of testing large individual blood samples. This pooled blood sampling technique might also applicable to the detection of other infectious diseases of bovines. In Chapters 7 and 8, the established MT-PCR assay using multiple markers for the detection of four genotypes (buffeli, chitose, ikeda and type 5) of T. orientalis was evaluated and modified to use one marker i.e., MPSP gene to detect, differentiate and quantitate these four genotypes in different countries. The MPSP gene was found to be a reliable and suitable marker to investigate the T. orientalis complex by standard PCR and MT-PCR assays. The findings of the present thesis highlight the need for further large-scale international collaborations to understand the genetic diversity, epidemiology, transmissions, host-parasite interactions, role of reservoir hosts, vaccines and treatment of T. orientalis complex in different parts of the world. It also suggests the need to develop other alternative, advanced molecular tools to simultaneously detect all the currently known and novel genotypes of T. orientalis using a next-generation sequencing approach.