School of Biological Sciences, University of Bristol, Bristol BS81UG, UK.
Parasitology. 2010 Oct;137(12):1799-804. doi: 10.1017/S0031182010000752. Epub 2010 Jun 14.
SUMMARYThe sheep ked has been largely eradicated in the UK but persists in the feral Soay sheep of St Kilda in the Outer Hebrides. Sheep keds transmit Trypanosoma melophagium, but parasitaemias are typically cryptic and this trypanosome has not been recorded in the St Kilda sheep. Trypanosomes were detected by PCR in preserved keds and were also found in gut smears from live keds; one infected gut was used to establish the trypanosome in vitro. Examination of the morphology of bloodstream forms from culture confirmed its identity as T. melophagium. Most keds were found to harbour the trypanosome, particularly those collected from lambs. DNA was extracted from preserved keds and from trypanosomes grown in vitro. Sequence analysis of the small subunit ribosomal RNA (SSU rRNA) gene and the spliced leader transcript showed the T. melophagium sequences to be very similar to those from T. theileri. A partial sequence of the ked SSU rRNA gene was also obtained. The close genetic relationship of T. melophagium and T. theileri suggests that T. melophagium represents a lineage of T. theileri that adapted to transmission by sheep keds and hence became a specific parasite of sheep.
在英国，绵羊虱蝇已基本被根除，但在外赫布里底群岛的圣基尔达野生斯莱格羊中仍有存在。绵羊虱蝇传播噬皮蝇锥体虫，但寄生血症通常是隐匿的，这种锥体虫尚未在圣基尔达绵羊中被记录。通过 PCR 在保存的虱蝇中检测到了锥虫，也在活体虱蝇的肠道涂片上发现了；用一只受感染的肠道建立了锥虫的体外培养。对培养的血液形式的形态学检查证实其为噬皮蝇锥体虫。从羔羊身上采集到的大多数虱蝇都携带有这种寄生虫。从保存的虱蝇和体外培养的锥虫中提取 DNA。小亚基核糖体 RNA（SSU rRNA）基因和拼接领导者转录物的序列分析表明，噬皮蝇锥体虫的序列与来自 T. theileri 的序列非常相似。还获得了虱蝇 SSU rRNA 基因的部分序列。噬皮蝇锥体虫和 T. theileri 之间的密切遗传关系表明，噬皮蝇锥体虫代表了 T. theileri 的一个谱系，它适应了通过绵羊虱蝇传播，并因此成为绵羊的一种特定寄生虫。
