Understanding the basis of strain restricted immunity to Theileria parva

在撒哈拉以南非洲，超过20%的人生活在贫困线以下，其中许多人居住在严重依赖牲畜为生的农村社区。传染病对这些地区的畜牧业生产有重大影响。牛的最重要的疾病之一是由蜱传寄生虫小泰勒虫引起的东海岸热（ECF）。这种疾病存在于东部和南部非洲的16个国家，是其中11个国家经济上最重要的牛病。据估计，ECF造成的经济损失每年超过3亿美元。越来越多地用于满足牛奶生产需求的进口牛种特别容易受到影响。尽管用抗寄生虫药物治疗受感染的动物和应用化学物质预防蜱虫侵扰可以用来控制ECF，但这些方法很难应用，而且贫困牲畜饲养者通常负担不起。因此，疫苗接种提供了一种更可持续的控制疾病的手段。牛可以通过感染活寄生虫并同时进行药物治疗来免疫疾病，但一种寄生虫菌株诱导的免疫力对所有其他菌株都无效。已发现使用3种寄生虫菌株的混合物进行疫苗接种可提供广泛的保护。这种疫苗已在当地使用，取得了一定的成功，但由于生产和分配方面的困难而阻碍了广泛应用。疫苗的抗原组成定义不明确，寄生虫菌株的含量是否是获得强大免疫力的最佳选择仍存在问题。最近，已经鉴定了由保护性细胞免疫应答识别的抗原，目的是研究它们用于开发亚单位疫苗的潜力。初步证据表明，这些抗原中有几种在寄生虫株之间存在差异。因此，了解T. parva是改进当前活疫苗和设计亚单位疫苗的关键问题。本项目的总体目标是了解T. parva，以开发针对ECF的改进疫苗。本研究的主要内容是：-对T。从肯尼亚不同地区的自然感染牛中分离parva，以确定寄生虫种群中抗原多样性的性质和程度。- 构成当前活疫苗的3种寄生虫分离株的抗原多样性分析。- 详细研究抗原的变化如何影响细胞免疫应答识别不同寄生虫菌株的能力。- 分析牛的细胞免疫反应的特异性，依次和同时免疫不同的寄生虫菌株，以了解这些免疫程序如何影响免疫反应的精细特异性。- 分析不同MHC基因型的免疫黑白花牛识别目前定义的T。parva抗原，以确定进一步抗原筛选的优先顺序。预期结果将提供用于改进当前活疫苗的质量控制的方法，鉴定可并入改进的第二代活疫苗中的寄生虫菌株，并指示哪些抗原和多少抗原将需要并入亚单位疫苗中。项目目标的实现将最终导致ECF疫苗的改进，从而更好地控制疾病。这将有助于确保受影响地区小农户和畜牧业者的资产并增加他们的收入。疾病控制的改善将导致肉类和牛奶产量的增加，并降低这些脆弱社区的贫困程度。

Over 20% of people in sub-Saharan Africa are classified as living below the poverty line and many of these people reside in rural communities that are heavily dependent on livestock for their livelihoods. Infectious diseases have a major impact on livestock production in these regions. One of the most important diseases of cattle is East Coast fever (ECF) caused by a tick-borne parasite Theileria parva. This disease is present in 16 countries in eastern and southern Africa and it is the most economically important cattle disease in 11 of these countries. Estimates of economic losses due to ECF exceed 300 million US dollars annually. Imported breeds of cattle, which are increasingly being used to satisfy demands for milk production, are particularly susceptible. Although treatment of infected animals with anti-parasitic drugs and application of chemicals to prevent tick infestation can be used to control ECF, these methods are difficult to apply and generally are unaffordable by poor livestock keepers. Vaccination, therefore offers a more sustainable means of controlling the disease. Cattle can be immunised against the disease by infection with live parasites and simultaneous drug treatment, but the immunity induced by one parasite strain is not effective against all other strains. Use of a mixture of 3 parasite strains for vaccination has been found to give broad protection. This vaccine has been used locally with some success, but widespread application has been hindered by difficulties in production and distribution. The antigenic composition of the vaccine is poorly defined and there remain questions as to whether the content of parasite strains is optimal for obtaining robust immunity. More recently, antigens recognised by the protective cellular immune responses have been identified, with the aim of investigating their potential for developing a subunit vaccine. Preliminary evidence indicates that several of these antigens vary between parasite strains. Hence, understanding antigenic variability in T. parva is a key issue both for improving the current live vaccine and for the design of a sub-unit vaccine. The overall aim of the current project is to understand the antigenic basis of strain restricted immunity to T. parva, in order to develop improved vaccines against ECF. The key elements of the proposed research are: - An analysis of T. parva isolates from naturally infected cattle in different regions of Kenya, to determine the nature and extent of antigenic diversity in the parasite population. - An analysis of antigenic diversity in the 3 parasite isolates that make up the current live vaccine. - A detailed study of how variation in the antigens affects the ability of the cellular immune response to recognise different parasite strains. - An analysis of the specificity of cellular immune responses in cattle immunised sequentially and simultaneous with different parasite strains, to understand how these immunisation procedures affect the fine specificity of the immune response. - Analysis of immune Friesian cattle of different MHC genotypes for their ability to recognise currently defined T. parva antigens, in order to identify priorities for further antigen screening. It is anticipated that the results will provide methods for improving quality control of the current live vaccine, identify parasite strains that could be incorporated into an improved second generation live vaccine and indicate which and how many antigens will need to be incorporated into a subunit vaccine. Realisation of the project objectives will ultimately result in improved vaccines for ECF leading to better control of the disease. This will help to secure the assets and increase the incomes of smallholder and pastoral livestock keepers in affected regions. Improved disease control will result in increased production of meat and milk and reduce the levels of poverty in these vulnerable communities.