Evaluation of a novel microbiological diagnostic test for latent tuberculosis infection in Ethiopia (Micro-LTBI)

结核病(TB)是一种细菌性传染病。它每年造成150万人死亡，其中95%发生在低收入和中等收入国家。这种疾病特别影响年轻人，给经济增长带来不利后果。在许多LMIC中，牛结核病(牛结核病)问题使这一问题更加严重。这种‘双重打击’在埃塞俄比亚是一个特别的问题，该国的人类结核病负担在世界上排名第十：牛结核病很普遍(患病率为5%-30%)，该国经济高度依赖养牛业。改善人类和牛的结核病控制将显著提高埃塞俄比亚和其他负担类似的低收入国家的经济增长和福利。大多数人类结核病病例是在潜伏的结核病感染重新激活导致疾病时出现的。潜伏性结核病感染在LMIC中非常常见，如果要消灭结核病，就需要对这一感染池进行治疗。抗生素治疗隐匿性结核病感染是有效的，但这种治疗方法的推广受到限制，因为缺乏针对这种疾病的准确的“金标准”诊断测试。现有的潜伏性结核病感染检测依赖于检测对细菌的免疫反应，而不是检测细菌本身。然而，在免疫检测呈阳性的人中，只有不到10%的人会继续发展为活动性结核病。这使得针对隐性结核病感染的抗生素治疗很难针对将从中受益的人。这种情况可能即将改变：最近，德国的一个研究小组(其中一人是这项拨款的共同申请者)报告说，他们能够在隐性结核病感染者的血液中检测到结核病细菌。细菌的数量非常少，需要相当大量的血液(100毫升)才能可靠地检测到它们。这一惊人的发现仅在生活在欧洲的七个人身上得到。下一步是在一个结核病流行的国家生活的更大的人群中进行新的测试。为了推进这一想法，我们在埃塞俄比亚和英国科学家之间建立了新的合作，他们共同拥有评估这一新测试所需的临床和技术技能的确切组合。我们将开展以下研究。首先，我们将招募200名最近接触过结核病传染性病例(‘结核病接触者’)的健康人员--100名亚的斯亚贝巴城市居民，他们曾接触住在家中的一名传染性肺结核病患者，以及100名农村牧民，他们曾接触一头患有牛结核病的牛。我们将在这些结核病接触者中进行新的血液测试，如果我们在血液中发现休眠的结核病细菌，我们将进行基因指纹识别，以确定在血流中发现的休眠细菌是否与从他们接触过的传染性结核病病例(人或牛)中分离出的细菌相同。如果结核病细菌的基因指纹是相同的，这将表明在潜伏期结核病感染者的血液中检测结核病细菌的可能性很小。我们还将招募40名即将开始对潜伏期结核病感染者进行抗生素治疗的人，并在治疗前后进行新的检测。如果我们发现抗生素治疗可以清除血液中的休眠结核病细菌，这将建议新测试的另一个潜在应用：监测休眠结核病感染对抗生素治疗的反应。这一点很重要，因为现有的测试不能判断抗生素治疗潜伏期结核病感染是否有效。综合起来，这些研究将让我们清楚地知道，德国团队的发现是否可以在LMIC环境中重现。如果是这样的话，我们将申请进一步的资金，以优化测试以使用较小的血量，并进行决定性的研究，以评估是否可以将其纳入LMIC现有的结核病控制计划。

Tuberculosis (TB) is a bacterial infectious disease. It causes 1.5 million deaths each year, 95% of which occur in low- and middle-income countries (LMICs). The disease particularly affects young adults, with adverse consequences for economic growth. In many LMICs, this problem is compounded by the problem of TB in cattle (bovine TB). This 'double-hit' is a particular problem in Ethiopia, which has the tenth highest burden of human TB in the world: bovine TB is widespread (prevalence 5-30%) and the country's economy is highly dependent on cattle farming. Improved TB control in humans and cattle would significantly enhance economic growth and welfare in Ethiopia and other similarly-burdened LMICs.Most TB cases in humans arise when a dormant TB infection re-activates to cause disease. Dormant TB infection is very common in LMICs and this pool of infection will need to be treated if TB is ever going to be eliminated. Antibiotic treatment for dormant TB infection is effective, but roll-out of this treatment is limited by the lack of an accurate 'gold standard' diagnostic test for the condition. Existing tests for dormant TB infection rely on detecting an immune response to the bacteria, rather than detecting the bacteria itself. However, less than 10% of those with a positive immune test ever go on to develop active TB. This makes it difficult to target antibiotic treatment for dormant TB infection at the people who will benefit from it.This situation could be about to change: very recently, a team of researchers in Germany (one of whom is a co-applicant on this grant) has reported that they have been able to detect TB bacteria in the blood of people with dormant TB infection. The number of bacteria is very small, and quite a large amount of blood (100 ml) is needed in order to detect them reliably. This remarkable finding has been made in just seven people living in Europe. The next step is to run the new test in a larger group of people who live in a country where TB is widespread. To take this idea forward, we have forged a new collaboration between Ethiopian and British scientists who together have the exact combination of clinical and technical skills needed to evaluate this new test.We will carry out the following studies. First, we will recruit 200 healthy people who have recently been in contact with an infectious case of TB ('TB contacts') - 100 urban residents of Addis Ababa who have been exposed to a person with infectious lung TB living in their home, and 100 rural cattle herders who have been exposed to a cow suffering from bovine TB. We will run the new blood test in these TB contacts, and, where we find dormant TB bacteria in the blood stream, we will do genetic fingerprinting to see if the dormant bacteria found in the bloodstream are identical to those isolated from the case of infectious TB (human or bovine) to which they were exposed. If the genetic fingerprints of the TB bacteria are the same, this will suggest that detection of TB bacteria in the blood of people with dormant TB infection is very unlikely to be a 'chance finding'.We will also recruit 40 people who are about to start antibiotic treatment for dormant TB infection, and run the new test before and after treatment. If we find that the antibiotic treatment clears dormant TB bacteria from the blood stream, this would suggest an additional potential application for the new test: monitoring response to antibiotic treatment of dormant TB infection. This is important, because existing tests cannot tell if antibiotic treatment for dormant TB infection has been effective or not.Taken together, these studies will give us a clear idea as to whether the findings of the German team can be reproduced in a LMIC setting. If so, then we will apply for further funding to optimise the test to use smaller blood volumes, and conduct definitive studies to evaluate whether it could be integrated into existing TB control programmes in LMICs.