Steyn H C, McCrindle C M E, Du Toit D
Onderstepoort Veterinary Institute, Private Bag X5, Onderstepoort, 0110 South Africa.
J S Afr Vet Assoc. 2010 Sep;81(3):160-5. doi: 10.4102/jsava.v81i3.140.
Heartwater, a tick-borne disease caused by Ehrlichia ruminantium, is considered to be a significant cause of mortality amongst domestic and wild ruminants in South Africa. The main vector is Amblyomma hebraeum and although previous epidemiological studies have outlined endemic areas based on mortalities, these have been limited by diagnostic methods which relied mainly on positive brain smears. The indirect fluorescent antibody test (IFA) has a low specificity for heartwater organisms as it cross-reacts with some other species. Since the advent of biotechnology and genomics, molecular epidemiology has evolved using the methodology of traditional epidemiology coupled with the new molecular techniques. A new quantitative real-time polymerase chain reaction (qPCR) test has been developed for rapid and accurate diagnosis of heartwater in the live animal. This method can also be used to survey populations of A. hebraeum ticks for heartwater. Sampling whole blood and ticks for this qPCR differs from routine serum sampling, which is used for many serological tests. Veterinary field staff, particularly animal health technicians, are involved in surveillance and monitoring of controlled and other diseases of animals in South Africa. However, it was found that the sampling of whole blood was not done correctly, probably because it is a new sampling technique specific for new technology, where the heartwater organism is much more labile than the serum antibodies required for other tests. This qPCR technique is highly sensitive and can diagnose heartwater in the living animal within 2 hours, in time to treat it. Poor sampling techniques that decrease the sensitivity of the test will, however, result in a false negative diagnosis. This paper describes the development of a skills training programme for para-veterinary field staff, to facilitate research into the molecular epidemiology of heartwater in ruminants and eliminate any sampling bias due to collection errors. Humane handling techniques were also included in the training, in line with the current focus on improved livestock welfare.
心水病是由反刍兽埃立克体引起的一种蜱传疾病，被认为是南非家养和野生反刍动物死亡的一个重要原因。主要传播媒介是南非牛蜱，尽管之前的流行病学研究已根据死亡率勾勒出了疫区，但这些研究受到诊断方法的限制，这些方法主要依赖阳性脑涂片。间接荧光抗体试验（IFA）对心水病病原体的特异性较低，因为它会与其他一些物种发生交叉反应。自生物技术和基因组学出现以来，分子流行病学已利用传统流行病学方法与新的分子技术相结合而得到发展。一种新的定量实时聚合酶链反应（qPCR）检测方法已被开发出来，用于对活体动物的心水病进行快速准确的诊断。该方法还可用于对南非牛蜱种群进行心水病调查。用于这种qPCR的全血和蜱虫采样不同于常规血清采样，常规血清采样用于许多血清学检测。南非的兽医现场工作人员，尤其是动物健康技术员，参与动物疫病的监测和监控工作。然而，发现全血采样操作不正确，可能是因为这是一种针对新技术的新采样技术，在心水病病原体比其他检测所需的血清抗体更不稳定。这种qPCR技术高度灵敏，能在2小时内诊断出活体动物的心水病，以便及时治疗。然而，降低检测灵敏度的不良采样技术将导致假阴性诊断。本文描述了为兽医辅助现场工作人员制定的一项技能培训计划，以促进对反刍兽心水病分子流行病学的研究，并消除因采集错误导致的任何采样偏差。培训中还纳入了人道处理技术，这与当前对改善家畜福利的关注相一致。
