Allsopp M T E P, Van Strijp M F, Faber E, Josemans A I, Allsopp B A
Onderstepoort Veterinary Institute, Private Bag X5, Onderstepoort 0110, South Africa.
Vet Microbiol. 2007 Feb 25;120(1-2):158-66. doi: 10.1016/j.vetmic.2006.10.026. Epub 2006 Oct 27.
In 1994 a batch of apparently healthy goats was selected for intended export to the USA from a heartwater-free and vector tick-free region of South Africa. The animals were tested serologically for heartwater, using either or both an IFA and an ELISA test, and 52% were found to be serologically positive. A PCR assay based on Ehrlichia ruminantium 16S gene sequences gave positive results for 54% of the animals, suggesting that apparently non-pathogenic E. ruminantium variants existed in this heartwater-free area. To identify and characterise the agents responsible for the positive serological and PCR results, ticks and animal blood samples were collected from two of the three farms involved in the original survey during two successive seasons of expected peak tick activity. Ticks were kept alive for a minimum of 3 weeks to allow digestion of any blood meal before being processed. Over the two seasons, 28% of the livestock and 15% of the ticks sampled were found to be carrying E. ruminantium. E. ruminantium 16S and pCS20 sequences were detected in all of the four tick species collected from the livestock (Rhipicephalus evertsi evertsi, Rhipicephalus evertsi mimeticus, Hyalomma truncatum, Hyalomma marginatum rufipes), suggesting that some of the species may act as vectors. Animals generally carried multiple E. ruminantium 16S genotypes, whereas ticks rarely carried more than one. Infection levels in both animals and ticks were too low to generate a marked response when a blood stabilate was sub-passaged in a clean sheep, preventing the subsequent establishment of any of the organisms in culture.
1994年,一批看似健康的山羊被挑选出来,准备从南非一个无牛心水病且无媒介蜱虫的地区出口到美国。使用间接荧光抗体试验(IFA)和酶联免疫吸附测定(ELISA)试验中的一种或两种对这些动物进行牛心水病血清学检测,结果发现52%的动物血清学呈阳性。基于反刍兽埃立克体16S基因序列的聚合酶链反应(PCR)检测显示,54%的动物呈阳性结果,这表明在这个无牛心水病的地区存在看似无致病性的反刍兽埃立克体变种。为了鉴定和表征导致血清学和PCR检测呈阳性的病原体,在预期蜱虫活动高峰期的两个连续季节,从最初调查涉及的三个农场中的两个农场采集了蜱虫和动物血液样本。蜱虫至少存活3周,以便在处理之前消化任何血餐。在这两个季节中,发现28%的家畜和15%的采集蜱虫携带反刍兽埃立克体。在从家畜身上采集的所有四种蜱虫(埃氏扇头蜱指名亚种、埃氏扇头蜱模仿亚种、截形璃眼蜱、边缘璃眼蜱红棕亚种)中均检测到反刍兽埃立克体16S和pCS20序列,这表明其中一些蜱虫种类可能是传播媒介。动物通常携带多种反刍兽埃立克体16S基因型,而蜱虫很少携带一种以上的基因型。当将血液稳定物在清洁绵羊中传代时,动物和蜱虫中的感染水平都太低,无法产生明显反应,从而阻止了随后在培养物中建立任何生物体。