Host genetic factors in susceptibility to mycobacterial disease in the African buffalo, Syncerus caffer

[摘要] ENGLISH ABSTRACT: Bovine tuberculosis (BTB) is a chronic, infectious disease found in domestic livestock and wildlife, and has serious biodiversity, economic and public health implications. African buffalo act as a wildlife reservoir of BTB, maintaining and transmitting the disease within the environment. The research presented in this thesis addresses the role of host genetic variation in resistance to BTB infection in African buffalo, and reviews the possible practical application of such information. Annual BTB prevalence within the African buffalo population in Hluhluwe iMfolozi Park, South Africa, was evaluated over a seven year period in order to define the extent of M. bovis infection. Prevalence changes over time suggest that the test and cull operation currently in place is performing successfully with respect to the original aims of the programme. A review of genetic studies of BTB in livestock and wildlife collated previous findings in this field and provided a collection of possible candidate genes and variants. It also highlighted a lack of research in wildlife, and the limitations of working with species with insufficient genetic data. To overcome the absence of whole-genome data, next-generation sequencing was performed on nine African buffalo, in order to identify novel genetic variants in this species. Upwards of 76 000 novel SNPs within gene regions were identified, and subsequent fluorescent genotyping of 173 SNPs showed a 57% validation rate. From the validated set, 69 SNPs located in genes related to the immune system were selected for association testing with BTB status in African buffalo, and were fluorescently genotyped in 868 individuals. Three SNPs, in the Solute Carrier family 7, member A13 (SLC7A13), Deleted in Malignant Brain Tumour-1 (DMBT1) and Interleukin 1 alpha (IL1α) genes, were identified as significantly associated with BTB status. Very little sequence information of the NRAMP1 (SLC11A1) gene was obtained from the next-generation sequencing performed, and this gene has been associated with brucellosis, salmonella and paratuberculosis in other animal species, making it an excellent candidate for BTB resistance. To characterise this gene in African buffalo, Sanger sequencing was performed to generate the complete coding region, and partially sequence the 5'UTR, intronic and 3'UTR regions. Fifteen novel polymorphisms and three microsatellites were identified within the gene. Finally, a review was prepared to assess the applicability of genetic information on BTB resistance to selective breeding programmes for African buffalo. Phenotypic, marker-assisted and genomic breeding strategies were discussed, with particular emphasis on their suitability to African buffalo. Identifying genes and variants involved in BTB resistance in African buffalo provides potential targets for drug or vaccine development, as well as information that could be incorporated into selective breeding programmes. This may support new management options for controlling the BTB epidemic in the game parks of South Africa, as an alternative to, or in conjunction with, lethal control

[发布机构] Stellenbosch University