The role of heartwater (Ehrlichia ruminantium infection) and other tick-borne pathogens in Acute Camel Death Syndrome in Kenya

单峰骆驼是肯尼亚北部重要的食物生产动物，对牧民社区的经济、粮食安全和福祉至关重要。他们的人口同比稳步增长，2016年超过320万。肯尼亚骆驼肉和奶业每年的产值约为1100万美元。急性骆驼死亡综合症(ACDS)是一种原因不明的新兴疾病，影响着肯尼亚北部部分地区的骆驼群。高达100%受影响的成年骆驼可以在不治疗的情况下死亡。与当地牧民熟知的其他骆驼疾病不同，ACDS是一种新的疾病，肯尼亚骆驼饲养者对此没有通用的名称。临床和尸检迹象显示出与心水的强烈相似之处，心水是一种由壁虱传播的绵羊、山羊和牛的疾病，在整个撒哈拉以南非洲都很流行，但在过去60年里，只有三次在非洲其他地区的骆驼身上被描述过。受影响的骆驼群可能严重感染扁虱，在受ACDS影响的骆驼身上取出的扁虱中已检测到心脏水的病原体--细胞内细菌Ehrlichiarumantium。然而，这并不能证明ACDS是骆驼心脏水的表现；其他扁虱传播的病原体(TBP)可能参与了这种综合征。识别ACDS的病原体是至关重要的，以便实施有效的预防和/或控制措施。为了调查心脏水和其他TPB在ACDS中的作用，我们建议在ACDs暴发地区对骆驼、与其并排吃草的绵羊和感染这两个物种的壁虱进行广泛调查。作为对照，我们将同样在未报告ACDS的地区对骆驼、绵羊和扁虱进行抽样。我们将采访骆驼饲养者，以确定他们对ACDs的先验知识，以及这种疾病与他们熟悉的其他骆驼疾病的不同之处，并确定他们在疫情爆发期间观察到的发病率、症状、死后体征和同时存在的扁虱感染水平。我们将收集骆驼和共同放牧的绵羊的血液和血清样本以及扁虱；将对血液样本进行筛选，以确定是否存在反胃肠杆菌和其他表明当前感染的TBP，并将对血清样本进行抗体检测，以确定是否存在反胃埃希菌和其他表明先前接触过的TBP。将对扁虱进行反胃埃希氏菌和其他TBP感染筛查，以确定在样本地区传播的病原体范围。我们将试图通过在牛和扁虱细胞系中培养来分离不同病原体的菌株；分离的新菌株的基因序列将与其他宿主的已知菌株的基因序列进行比较，以寻找可能解释ACDS作为一种新的骆驼疾病出现的差异。如果我们的任何研究地区在计划期间爆发ACDs，我们会从受影响的骆驼身上收集临床和验尸样本，并以与调查样本相同的方式进行处理。我们将把等分的骆驼和扁虱样本储存在低温储存库中，从而创建一个资源，供未来对骆驼传染性疾病的研究以及研究影响骆驼健康的其他因素的科学家使用。我们项目的一个重要元素将是与急性传染性疾病相关的能力建设，更广泛地说，是肯尼亚的骆驼健康。我们将利用从实地和实验室研究中获得的知识，制定诊断、治疗和控制急性传染病的方案，包括有关适当抽样技术的动手培训，以及适当储存和运送样本到实验室。此外，我们将为一名肯尼亚硕士学生提供机会和支持，让他们开展专注于我们建议研究的特定方面的研究项目。

Dromedary camels are important food-producing animals in northern Kenya and vital for the economy, food security and well-being of pastoralist communities. Their population is steadily increasing year-on-year and stood at over 3.2 million in 2016. The Kenyan camel meat and milk industry is worth approximately US$11 million annually. Acute Camel Death Syndrome (ACDS) is an emerging disease of unknown cause affecting camel herds in parts of northern Kenya. Up to 100% of affected adult camels can die without treatment. Unlike other camel diseases that are well-recognised by local pastoralists, ACDS is a new disease for which Kenyan camel keepers have no vernacular name. Clinical and post-mortem signs show strong similarities to heartwater, a tick-borne disease of sheep, goats and cattle that is endemic throughout sub-Saharan Africa, but has only been described in camels in other parts of Africa on three occasions in the past 60 years. Affected camel herds may be heavily infested with ticks, and the causative agent of heartwater, the intracellular bacterium Ehrlichia ruminantium, has been detected in ticks removed from camels affected by ACDS. However this does not prove that ACDS is a manifestation of heartwater in camels; other tick-borne pathogens (TBP) may be involved in the syndrome.It is essential to identify the causative agent of ACDS so that effective preventive and/or control measures can be implemented.To investigate the role of heartwater and other TPB in ACDS, we propose to carry out a broad-spectrum survey of camels, sheep that graze alongside them, and ticks infesting both species, in areas where ACDS outbreaks have occurred. As controls, we will similarly sample camels, sheep and ticks in areas where ACDS has not been reported. We will interview camel keepers to determine their prior knowledge of ACDS and how it is distinct from other camel diseases with which they are familiar, and to establish disease incidence, symptoms, post mortem signs and concurrent levels of tick infestation that they have observed during outbreaks. We will collect blood and serum samples and ticks from camels and co-grazing sheep; blood samples will be screened for presence of E. ruminantium and other TBP indicating current infection and serum samples will be tested for antibodies to E. ruminantium and other TBP indicating previous exposure. Ticks will be screened for infection with E. ruminantium and other TBP to determine the range of pathogens circulating in the sample areas. We will attempt to isolate strains of the different pathogens by culturing them in bovine and tick cell lines; gene sequences of isolated novel strains will be compared with those of known strains from other hosts to look for differences that might explain the emergence of ACDS as a new camel disease. If there is an outbreak of ACDS in any of our study areas during the project, we will collect clinical and post-mortem samples from affected camels and process them in the same way as the survey samples. We will bank aliquots of the camel and tick samples in cryostorage, thereby creating a resource for use in future studies on ACDS and by scientists researching other factors affecting camel health.An important element of our project will be capacity-building relating to ACDS and more generally to camel health in Kenya. Using the knowledge gained from our field and laboratory studies, we will formulate protocols for diagnosis, treatment and control of ACDS, including hands-on training in appropriate sampling techniques and proper storage and transport of samples to the laboratory. In addition, we will provide the opportunity and support for a Kenyan MSc student to carry out their research project focussing on a particular aspect of our proposed study.